Either the actual current in the protective conductor was measured, or a simple resistor-capacitor network representing a simple body model was used, the leakage current being defined as
Test site environment
The environmental requirements for test sites must adhere to the specifications outlined in the EQUIPMENT standard In cases where limit values are set below 70 àA r.m.s or 100 àA peak, or if the EQUIPMENT includes large shields potentially influenced by high-frequency signals, product committees should consult Annex B for guidance.
Test transformer
Using a test transformer for isolation is optional; however, for optimal safety, it is recommended to utilize a test transformer for isolation (T2 in Figure 2, T in Figures 6 to 14) and ensure that the main protective earthing terminal of the Equipment Under Test (EUT) is properly earthed It is important to consider any capacitive leakage in the transformer Alternatively, if the EUT is not earthed, the test transformer secondary and the EUT can be left floating, eliminating the need to account for capacitive leakage in the test transformer.
When a transformer T is not utilized, the Equipment Under Test (EUT) must be placed on an insulating stand, and necessary safety measures should be implemented due to the risk of the EUT's body being at a dangerous voltage level.
Earthed neutral conductor
EQUIPMENT intended for connection to a TT or TN power distribution system shall be tested with minimum voltage between neutral and earth
NOTE Descriptions of various power distribution systems are given in Annex I
The protective conductor and the earthed neutral conductor for the EUT should have a voltage difference of less than 1 % of line-to-line voltage (see example in Figure 1)
A local transformer, see 4.2, will achieve this requirement
Alternatively, if the voltage difference is 1 % or more, the following are examples of methods which, in some cases, will avoid measurement errors due to this voltage:
To ensure proper measurement and safety, connect the terminal B electrode of the measuring instrument network to the neutral terminal of the Equipment Under Test (EUT) rather than the protective earthing conductor Additionally, the earthing terminal of the EUT should be connected to the neutral conductor instead of the protective earthing conductor of the supply.
Figure 1 – Example of earthed neutral, direct supply
Figure 2 – Example of earthed neutral, with transformer for isolation
Selection of measuring network
General
Measurements shall be made with one of the networks of Figure 3, Figure 4 and Figure 5
NOTE See Annexes E, F and G for further explanation of the three networks
Figure 3 – Measuring network, unweighted touch current
Figure 4 – Measuring network, touch current weighted for perception or startle-reaction
NOTE For special conditions on the use of this network, see 5.1.2
Figure 5 – Measuring network, touch current weighted for letgo-immobilization
Perception and startle-reaction
The circuit depicted in Figure 4 is designed for low-level electric shock limits, specifically applicable when the alternating current (a.c.) limit value in the product standard is up to 2 mA r.m.s or 2.8 mA peak.
Letgo-immobilization
The circuit depicted in Figure 5 is designed for applications requiring higher electric shock limits, specifically when the alternating current (a.c.) limit value in the product standard exceeds 2 mA r.m.s or 2.8 mA peak.
Electric burn (a.c.)
The unweighted TOUCH CURRENT network of Figure 3 shall be used.
Ripple-free d.c
Any one of the three networks shall be used Unless otherwise specified in the EQUIPMENT standard, ripple-free d.c means less than 10 % peak-to-peak ripple
Test electrodes
Construction
Unless otherwise specified in the EQUIPMENT standard, the test electrodes shall be
– a 10 cm × 20 cm metal foil to represent the human hand Where adhesive metal foil is used, the adhesive shall be conductive.
Connection
Test electrodes shall be connected to test terminals A and B of the measuring network.
Configuration
The Equipment Under Test (EUT) must be completely assembled and configured to its maximum capacity It should also be connected to external signal voltages as specified by the manufacturer for optimal performance.
EQUIPMENT which is designed for multiple power sources, only one of which is required at a time (for example, for backup), shall be tested with only one source connected
EQUIPMENT requiring power simultaneously from two or more power sources shall be tested with all power sources connected but with not more than one connection to protective earth.
Power connections during test
General
NOTE Examples of power distribution systems are given in Annex I
EQUIPMENT shall be connected in a test configuration as shown in Figure 6 to Figure 14, according to 5.4.2, 5.4.3 or 5.4.4, as appropriate
Equipment committees should evaluate the necessity for manufacturers to specify the type of power distribution system (TN, TT, IT) that the equipment is designed to connect to in its final application.
If the EUT is specified by the manufacturer for use only on certain power distribution systems, the EUT shall be tested only when connected to those systems
Equipment intended for connection to TN or TT systems must adhere to the requirements outlined in section 5.4.2 Additionally, equipment that connects to IT systems must comply with section 5.4.3, but it can also be connected to TN or TT systems.
For Class 0 and Class II EQUIPMENT (see IEC 61140), the protective conductors in Figure 6 through Figure 14 are ignored
Figure 6 – Single-phase equipment on star TN or TT system
The centre-tapped winding may be one leg of a delta supply
Figure 7 – Single-phase equipment on centre-earthed TN or TT system
Figure 8 – Single-phase equipment connected line-to-line on star TN or TT system
The 1 000 Ω resistor should be rated for supply system faults
Figure 9 – Single-phase equipment connected line-to-neutral on star IT system
The 1 000 Ω resistor should be rated for supply system faults
Figure 10 – Single-phase equipment connected line-to-line on star IT system
Figure 11 – Three-phase equipment on star TN or TT system
The 1 000 Ω resistor should be rated for supply system faults
Figure 12 – Three-phase equipment on star IT system
In equipment featuring both a three-phase load and a center-earthed single-phase load, it is essential to identify the earthed side The switch, designated as switch g, must remain in the position marked as the earthed side.
Figure 14 – Three-phase equipment on centre-earthed delta system
Equipment for use only on TN or TT star power distribution systems
Three-phase equipment must be connected to a three-phase star power distribution system with an earthed neutral Single-phase equipment should connect between the phase and neutral of this earthed neutral system or, as specified by the manufacturer, line-to-line on a center-earthed three-phase star power distribution system.
Equipment for use on IT power distribution systems including
Three-phase equipment must be connected to a suitable three-phase IT power supply system, while single-phase equipment should be connected between phase and neutral or, if specified by the manufacturer, line-to-line.
Equipment for use on single-phase centre-earthed power supply
centre-earthed delta power supply systems
Single-phase EQUIPMENT shall be connected to a supply having its centre tap earthed (see Figure 7 and Figure 14)
Three-phase EQUIPMENT shall be connected to the appropriate delta supply (see Figure 14).
Supply voltage and frequency
Supply voltage
Supply voltage shall be measured at the EQUIPMENT supply terminals
Traditionally, maximum TOUCH CURRENT occurred at the highest supply voltage; however, modern electronic power supplies may not always deliver this Instead, TOUCH CURRENT can peak at lower voltages or under different conditions It is essential to ensure electric shock protection is in place for the worst-case operating scenario.
EQUIPMENT rated for a single voltage shall be tested at its rated voltage plus an appropriate working tolerance to allow for supply variations
Equipment designed for a specific nominal voltage range must undergo testing at both the lower and upper limits of that range, along with an appropriate working tolerance to accommodate supply fluctuations This working tolerance is established by the equipment committee or, if needed, by the manufacturer, typically set at values such as 0 %, -10 %/+6 %, or +10 %.
Equipment designed for various nominal voltages or voltage ranges must be configured to the highest nominal voltage or range using a voltage selector In cases where voltage selection requires intricate switching beyond simple transformer winding adjustments, further testing may be needed to identify the worst-case scenario.
If testing EQUIPMENT at the specified voltage is impractical, it is acceptable to conduct tests at any available voltage within the EQUIPMENT's rating and subsequently calculate the results.
Supply frequency
Supply frequency shall be the maximum rated nominal frequency, or alternatively, measurements may be corrected by calculation for estimation of the worst case current
General
Touch current measurements
Product committees might consider omitting the measurement of TOUCH CURRENT in certain accessible areas, following the voltage limitation principle outlined in IEC 60364-4-41 In such cases, measurements should first be taken for accessible voltage, and subsequently, if necessary, for either weighted or unweighted TOUCH CURRENT as specified in Clause 6.
Concerns regarding the effects of electric burns can occur with direct current (d.c.) or at high frequencies, particularly above 30 kHz for a touch current of 3.5 mA At lower frequencies, the primary considerations are startle reactions and the inability to let go In situations where these concerns are present, it is essential to measure the unweighted root mean square (r.m.s.) value of the touch current, along with assessments for either startle reactions or the inability to release.
Control switches, equipment and supply conditions
During TOUCH CURRENT measurements, the test environment, configuration, earthing and supply system shall be according to 5.3, 5.4 and 5.5
To optimize measurement values, the configuration should be adjusted by connecting and disconnecting units of the EQUIPMENT, in accordance with the manufacturer's operating and installation guidelines.
Control switches e, g, l, n, and p, as shown in Figures 6 to 14, should be adjusted according to the guidelines in section 6.2, while independently varying the conditions specified in this subclause and section 6.2.1 to achieve the highest measured values Product committees are responsible for selecting the appropriate variables The recent inclusion of ABNORMAL OPERATION as an operating condition in product standards related to electrical installations, such as loss of PE or inability to ensure supply polarity, clarifies the testing conditions for both NORMAL operation and FAULT CONDITIONS.
Use of measuring networks
To measure TOUCH CURRENT between simultaneously accessible parts and between accessible parts and earth, it is essential to use suitable measuring electrodes, a measuring network, and a measuring device, as outlined in sections 5.1, 5.2, and G.4 These measurements should adhere to the appropriate systems illustrated in Figures 6 to 14, as referenced in section 5.4.
The terminal A electrode shall be applied to each accessible part in turn
For each application of the terminal A electrode, the terminal B electrode shall be applied to earth, then applied to each of the other accessible parts in turn
In power systems featuring an earthed power conductor, the terminal B electrode can be directly linked to the earthed power conductor at the interface between the equipment under test (EUT) and the power supply, rather than being connected to the protective conductor This direct connection is permissible even if the voltage difference between the protective conductor and the earthed power conductor exceeds 1% of the line-to-line voltage.
Normal and fault conditions of equipment
Normal operation of equipment
The test is carried out with terminal A of the measuring network connected to each unearthed or conductive accessible part and circuit in turn, with all test switches l, n and e closed
Measurements shall be made in all applicable conditions of normal operation
Examples of normal operation include mains switch on, mains switch off, standby, start-up, heating and any setting of operator controls except supply-voltage-setting controls
Single-phase EQUIPMENT shall be tested in normal and reverse polarity (switch p)
Three-phase EQUIPMENT shall be tested with phase reversals, unless EQUIPMENT operation is dependent on phasing.
Equipment and supply fault conditions
For EQUIPMENT having no connection to earth, 6.2.2 does not apply
For EQUIPMENT having a protective earthing connection or a functional earthing connection, terminal A of the measuring network is connected to the EQUIPMENT earthing terminal of the EUT
Measurements must be conducted for each applicable fault condition outlined in sections 6.2.2.2 to 6.2.2.9 Each fault should be applied individually, including any logically resulting faults from the initial one Prior to applying any fault, the EQUIPMENT must be restored to its original state, free from faults or consequential damage.
In three-phase equipment utilizing a balanced line filter, the theoretical net current to earth is zero However, due to component and voltage unbalance, a finite net current is typically observed, which may not be captured during type testing Additionally, a failed capacitor in one phase can lead to increased unbalanced currents.
EQUIPMENT committees should consider including a test for such EQUIPMENT, involving the substitution of a deliberately faulted filter (one capacitor removed), together with a loss of protective earth connection (see 6.2.2.2)
Similar considerations apply to a balanced arrangement of other components, such as surge arrestors, connected between mains and earth
Three-phase EQUIPMENT shall be tested with phase reversals unless EQUIPMENT operation is dependent on phasing
Depending on the kind of EQUIPMENT, several safety degrees of the protective conductor are to be distinguished (see IEC 61140)
Single-phase EQUIPMENT not reliably earthed shall be tested with loss of protective earth connection (switch e) in combination with normal and reverse polarity (switch p)
Three-phase EQUIPMENT not reliably earthed shall be tested with loss of protective earth connection (switch e)
The requirements outlined in this subclause do not apply to reliably earthed equipment that is connected to the supply either permanently or through industrial-grade plugs and sockets, such as those specified in IEC 60309-1 or an equivalent national standard, unless the product committee decides otherwise.
Single-phase EQUIPMENT shall be tested with neutral open (switch n), with earth intact and in normal polarity, and again in reverse polarity (switch p)
EQUIPMENT for use on IT systems shall be tested with each phase conductor faulted to earth, one at a time (switch g)
Three-phase EQUIPMENT shall be tested with each phase conductor open, one at a time (switches l)
Single-phase equipment designed for IT power systems or three-phase delta systems must undergo testing using a three-phase power system, where each phase is individually faulted to earth.
(switch g), in combination with normal and reverse polarity (switch p) and separately with each phase conductor open one at a time (switches l), and in combination with normal and reverse polarity (switch p)
Three-phase EQUIPMENT for use on centre-earthed delta supply systems shall be tested on a delta supply system with each delta-leg centre-earthed, one at a time (switch g)
Equipment with both three-phase and centre-earthed circuits that cannot be installed independently and have a designated earthed leg must be tested using switch g in the identified earth-leg position only.
Other faults as specified by the product committee shall be simulated if they are likely to increase TOUCH CURRENT
Accessible conductive parts that are incidentally electrically connected to other components must be tested in both connected and disconnected states For further details, refer to Annex C concerning incidentally connected parts.
Perception, startle-reaction and letgo-immobilization
The voltages U2 and U3, as shown in Figures 4 and 5, represent frequency-weighted values of U1, providing a single low-frequency equivalent indication of TOUCH CURRENT for all frequencies above 15 Hz These weighted TOUCH CURRENT values are determined by taking the highest measured values of U2 and U3 during the procedure outlined in Clause 6 and dividing them by 500 Ω The maximum values are then compared to the perception, startle-reaction, and letgo-immobilization limits specified for the EQUIPMENT, such as the 50 Hz or 60 Hz limit values.
Measurements for d.c limits are made in a like manner, but taken as U 1 divided by 500 Ω(see also Annex G).
Electric burn
To assess the effects of electric burns, the unweighted root mean square (r.m.s.) or direct current (d.c.) value of touch current is measured This measurement is derived from the r.m.s voltage \( U_1 \) across a 500 Ω resistor in the measuring network.
The impact of TOUCH CURRENT is influenced by both the contact area with the human body and the duration of that contact These factors play a crucial role in determining the overall effect experienced.
TOUCH CURRENT limits are not in the scope of this standard (see also Clause D.3)
Electric burns occur when electrical current passes through the resistance of human skin and body, leading to power dissipation Additionally, burns can also arise from electrical equipment, particularly due to arcing or its by-products.
8 Measurement of protective conductor current
General
Current requirements and values for protective conductors are not related to TOUCH CURRENT concerns and, therefore, such limits and methods of measurement are dealt with separately.
Multiple equipment
Within any shared earthing system, the PROTECTIVE CONDUCTOR CURRENTS of individual
The protective conductor current of a group of equipment earthed by a single protective earthing conductor cannot be accurately predicted based on the individual equipment protective conductor currents As a result, measurements taken on individual equipment have limited applicability Therefore, it is essential to measure the protective conductor current for the entire group directly in the shared protective earthing conductor.
Measuring method
The PROTECTIVE CONDUCTOR CURRENT must be measured post-installation by placing an ammeter with negligible impedance, such as 0.5 Ω, in series with the protective conductor This measurement is essential for ensuring the effectiveness of the protective conductor.
EQUIPMENT and power distribution system running in all normal operating modes
Unless otherwise defined in the EQUIPMENT standard, an EQUIPMENT is identified as having a single connection to a supply of electricity
An EQUIPMENT may be a single unit or may consist of physically separate, electrically interconnected units (see Figure A.1) The source of electricity may be contained within the
EQUIPMENT (for example, solar or battery power)
The connection of signal cables shall be considered as part of the EQUIPMENT, in accordance with 5.4
Supply connection compatible with local supply
Supply connection not designed to be connected directly to local supply
When testing equipment with touch current limits below 70 µA r.m.s or 100 µA peak, especially those with significant capacitive coupling to outer surfaces at high frequencies, it is essential to measure the capacitively coupled current on a conductive surface beneath or against the equipment For accurate testing, the equipment should be positioned on a conductive plane that is supported by an insulating surface.
The conductive plane shall be equal to or greater than the adjacent EQUIPMENT surface in area and perimeter
Measurements shall be according to Clause 6, with the conductive plane tested as an accessible part
The measurements shall be repeated with the conductive plane placed against any other surface of the EQUIPMENT which may become adjacent to an outside conductive plane
For purposes of isolation from electromagnetic interference, it may be necessary to place the
EQUIPMENT (including the conductive plane, if used) 0,5 m or more from other conductors or
Incidentally connected parts are accessible conductive parts which are neither reliably connected to, nor positively isolated from, earth or any specified voltage
Examples of incidentally connected parts include
– doors and assemblies attached by metal hinges,
– adhesively-bonded labels which have an accessible conductive part (for example, metal foil),
– parts which are attached to painted or anodised surfaces,
Some production samples of the EQUIPMENT may have a part that is either effectively connected to earth or another circuit, while in other samples, the same part may be isolated To determine the worst-case scenario for TOUCH CURRENT, it is essential to measure it for both configurations, as it is unclear which will yield a higher current However, when the predominant frequency is below 100 Hz, the worst-case scenario is likely when the incidentally connected part is linked to other components.
General
In developing the procedures outlined in this standard, specific assumptions were made regarding the current limits utilized by product committees This approach was essential for selecting the relevant data from IEC TS 60479-1 to inform the design of the measuring networks depicted in Figures 3, 4, and 5.
The current values provided in this annex are illustrative examples intended to assist product committees in determining appropriate current limits, based on earlier IEC publications.
Limit examples
Ventricular fibrillation
It is assumed that the limits chosen for TOUCH CURRENTS will be well below the threshold for ventricular fibrillation.
Inability to letgo-immobilization
The method of measurement is specified in this standard
IEC TS 60479-1 identifies 10 mA r.m.s as the average threshold for letgo-immobilization current, while a proposed level of 5 mA r.m.s would encompass the entire adult population Refer to Figure F.3 for frequency effects.
Startle-reaction
The method of measurement is specified in this standard
The startle-reaction threshold given in IEC TS 60479-1 is approximately 0,5 mA r.m.s for low frequencies Various limits are in use between the thresholds for startle-reaction and letgo- immobilization.
Perception threshold
Touch currents can be detected at levels as low as a few microamperes These small currents are generally not deemed hazardous unless they reach a level that triggers an involuntary startle reaction, which could lead to harmful effects Consequently, such low touch currents are typically not measured by standard methods.
Special applications
The method of measurement specified in this standard can be used, unless otherwise specified in the applicable standard for the particular product
0,25 mA r.m.s (one half of the startle-reaction threshold) is used for Class II EQUIPMENT in product standards such as IEC 60065, IEC 60335-1, IEC 60950-1 and IEC 62368-1 See Figure F.2 for frequency effects
For certain medical applications, limits below 0.25 mA r.m.s are established In these cases, the measurement method outlined in this standard may not accurately represent the appropriate body impedance model (refer to Clause E.1).
Choice of limits
Consideration should be given to the need to specify different limits for (1) normal operating conditions and (2) fault conditions
See IEC TS 60479 series for guidance on the effects of current passing through the human body
Limits for d.c and a.c are typically defined for frequencies up to 100 Hz, with measurement methods consistent across letgo-immobilization, startle-reaction, and specific applications Measuring networks account for the impact of higher-frequency currents on the body, simulating reduced body impedance as frequency rises The peak current values, adjusted for frequency, are crucial for assessing letgo-immobilization, startle-reaction, and perception, while r.m.s values are important for evaluating electric burns However, within this standard's scope, frequency effects on electric burns are minimal, as the primary concern at low frequencies is the startle-reaction or letgo-immobilization.
Most equipment does not require limits based on ventricular fibrillation, as the lower touch current limits for startle-reaction or let-go immobilization typically prevent this condition However, an exception exists, as noted in IEC TS 60479-1, where a short-duration current impulse may pass through the body without causing an inability to let go, and the resulting startle-reaction is deemed non-hazardous.
The traditional view of the inability to let go has primarily focused on grippable parts, but this perspective is now seen as overly simplistic In this context, the maximum continuous current limit aligns with letgo-immobilization, with the exception of electric burn considerations Electric burn becomes a significant concern primarily at high frequencies Within the limits for startle reaction and letgo-immobilization, there exists a secondary safety risk from surprise or involuntary muscle reactions; however, direct injury from current passing through the body is not anticipated Such current levels may be deemed acceptable under single fault conditions, provided that product committees explicitly allow for exemptions.
For short-duration currents, a limit value exceeding that of letgo-immobilization may be applied, as long as it remains significantly below the thresholds for ventricular fibrillation and electric burn Product committees may define the network in Figure F.3 for AC measurements where minimal area contact is anticipated.
The startle-reaction network of Figure 4 should be used for measurements where the startle- reaction limit is used for small area contact
It is understood that the limit values for low-frequency TOUCH CURRENT in other IEC publications are based upon the following considerations
– Limits for startle-reaction and lower limits:
• need to avoid involuntary startle-reaction, where severe consequences may result (for example, falling from a ladder or dropping EQUIPMENT);
• the limit for startle-reaction is generally 0,5 mA r.m.s or 0,7 mA peak for a sinusoidal current;
• a limit lower than 0,25 mA r.m.s (0,35 mA peak) is indicated where the user is particularly sensitive or at risk due to environmental or biological reasons
• startle and some reaction are acceptable as an indication of a first fault, when the letgo-immobilization limit is applied;
• men and women are estimated to have an average letgo-immobilization threshold of
Research indicates that a significant portion of the population exhibits varying sensitivity levels, with the 99.5th percentiles showing threshold values of 9 mA r.m.s for men and 6 mA r.m.s for women Additionally, it is anticipated that threshold values for children will be even lower.
• certain single fault conditions may justify letgo-immobilization limits, with startle- reaction limits applying for normal (non-fault) conditions
Some types of equipment may exhibit a high initial touch current upon being powered on, but this current decreases quickly during operation Typically, this factor is overlooked when establishing equipment limits as determined by the product committee.
Electric burn effects of touch current
There is no universally accepted threshold for TOUCH CURRENT that can completely prevent ELECTRIC BURNS in every situation Factors such as the contact area with the human body and the duration of contact play significant roles Further research is needed to understand the relationship between these parameters Once safe limits are determined, they may involve two or more of these factors.
The method of measurement of TOUCH CURRENT for consideration of ELECTRIC BURN effects is specified in this standard (see 7.2)
The following limit has been used in an IEC standard:
– IEC 61010-1: 500 mA r.m.s (under fault conditions)
It is reported that skin burns begin to occur at current densities of about 300 mA r.m.s./cm 2 to
400 mA r.m.s./cm 2 (Becker, Malhotra and Hedley-Whyte)
An analysis of the conditions that lead to electric burns indicates a crossover frequency at which electric burns surpass letgo-immobilization thresholds Consequently, product requirements must emphasize accurate measurements to ensure adequate protection The IEC 62368-1 standard offers a framework for establishing these essential requirements.
Networks for use in measurement of touch current
General
Current values given in this annex are only examples
The networks illustrated in Figures 3, 4, and 5 are designed for measuring TOUCH CURRENT, adhering to standard limits set by product committees They accommodate a range from 100 µA r.m.s./140 µA peak to approximately 10 mA r.m.s./14 mA peak for both a.c and d.c currents, while also supporting a frequency range up to 1 MHz for sinusoidal, mixed frequency, and non-sinusoidal waveforms.
Body impedance network – Figure 3
The purpose of the network of Figure 3 is to
– simulate the impedance of the human body,
– provide a measurement indicating the level of current which can flow through a human body if the body contacts the EQUIPMENT in a like manner
R B models the internal impedance of the human body
The R S and C S models represent the total skin impedance at two contact points, with the value of C S being influenced by the area of skin contact Larger contact areas correspond to higher capacitance values, such as 0.33 µF.
The human body model depicted in Figure 3, along with the associated R and C values, has been a standard in product safety regulations for over 50 years, demonstrating a proven track record of effectiveness in this measurement.
TOUCH CURRENT with regard to ELECTRIC BURN is equal to U 1 r.m.s divided by 500 Ω.
Startle-reaction (and body impedance) network – Figure 4
Startle-reaction by the human body is the result of current flowing in the internal portions of the body
Accurate measurement of startle-reaction effects necessitates consideration and compensation for frequency variation The network illustrated in Figure 4 simulates body impedance and assigns weighting to align with the body's frequency characteristics in response to current that induces involuntary startle reactions It is assumed that the frequency characteristics for both reaction and startle are identical, with the data for these characteristics derived from tests conducted on the threshold of startle.
The measurement network is usable for current limits up to the weighted equivalent of about
The measurement of higher level limits using a network with 2 mA r.m.s at 50 Hz and 60 Hz is limited by letgo-immobilization considerations Additionally, different frequency weighting is required when the inability to let go poses a concern at these elevated levels (refer to Clause E.4).
The a.c or d.c TOUCH CURRENT with regard to startle-reaction is equal to U 2 peak divided by
Letgo-immobilization (and body impedance) network – Figure 5
Immobilization, or the inability to release an object, is influenced by the internal flow of current within the body, particularly through the muscles The measurement network is designed to effectively handle current levels exceeding approximately 2 mA r.m.s at both 50 Hz and 60 Hz.
The impact of frequency on letgo-immobilization limits differs significantly from its influence on startle reactions and electric burns, particularly at frequencies exceeding 1 kHz, where filter design considerations are crucial.
The network illustrated in Figure 5 models body impedance and is designed to align with the body's frequency response to currents that may induce tetanization, leading to involuntary muscle contractions and an inability to release The TOUCH CURRENT related to letgo-immobilization is calculated as U 3 peak divided by 500 Ω.
Measuring network limitations and construction
The networks illustrated in Figures 3, 4, and 5 are designed to generate a measurable voltage response that closely resembles the curves shown in Figures F.1, F.2, and F.3 These networks and reference curves align generally with the standards outlined in IEC TS 60479-1 and IEC TS 60479-2, with minor deviations permitted at the curve inflections between 300 Hz and 10 kHz for the sake of measurement circuit simplicity.
When limits for electric burn are defined, touch current is also assessed without frequency weighting The established criteria for electric burn take precedence over those for startle reaction or letgo immobilization if the root mean square (r.m.s.) current limit for electric burn is surpassed before reaching the weighted peak current limits for the other reactions This situation typically occurs within the frequency range of 30 kHz to 500 kHz, influenced by the current waveform and limit values In the absence of such predominant frequencies, measuring the electric burn limit is unnecessary.
Figure F.1 – Frequency factor for electric burn
Figure F.2 – Frequency factor for perception or startle-reaction
Figure F.3 – Frequency factor for letgo-immobilization
Construction and application of touch current measuring instruments
Considerations for selection of components
General
The choice of components for the TOUCH CURRENT measuring networks, as illustrated in Figures F.3, 4, and 5, is significantly influenced by the specific application, including the current levels and frequencies to be measured, as well as the necessary tolerances and power handling capabilities.
The measuring networks and instruments and the performance specifications discussed in this standard are appropriate for both sinusoidal TOUCH CURRENT waveforms from simple
For applications involving non-sinusoidal touch current waveforms generated by advanced products with high frequencies, it may not be essential for a network to accommodate the full range from direct current (d.c.) to 1 MHz or to endure unlikely power input levels In such cases, simpler current measuring networks and instruments can effectively replace the specified ones, as long as the circuit conditions ensure that the readings remain consistent.
Information provided here is intended to point out the factors to be considered for each component, so that appropriate decisions can be made for particular applications.
Power rating and inductance for R S and R B
Power in resistors R S and R B is influenced by two main factors: the potential for overload at direct current (d.c.) or low frequencies For instance, if a 240 V 50 Hz/60 Hz overload capability is required, R S must handle 21.6 W and R B must manage 7.2 W for a brief period without altering their values Conversely, if overloads are not a concern, using 1/2 W or 1 W metal film resistors can ensure sufficient accuracy, along with a low temperature coefficient and long-term stability.
Based on the above choices, the measuring network should be appropriately marked, unless it is capable of withstanding continuous overloads
In certain applications, resistor R B can dissipate power from high-frequency currents For instance, measuring a current at a burn hazard level of 500 mA would result in a power dissipation of 125 W in R B While this scenario is unlikely, selecting a resistor with such capabilities is a viable option.
Wire wound power resistors can effectively manage power when factors like accuracy and inductive errors are maintained within acceptable limits for specific applications These resistors typically offer accuracies of ± 1% and ± 5% Measurements on standard 12 W and 20 W wire wound resistors indicate an inductance of approximately 30 µH.
1 000 Ω value Two such resistors in parallel give 500 Ω and the inductance would cause a
The impedance increases by 2% to 510 Ω at 1 MHz, influenced by the resistor R S and capacitor C S, which regulate the high-frequency performance of the R S /R B network Additionally, an unexpected inductance of 1 mH in series with R S (1,500 Ω) results in a minimal effect of less than 0.2% at 1 MHz.
Capacitor C S
For optimal performance, it is advisable to use film capacitors with extended foil construction Capacitor C S should have a voltage rating that can handle short-term overloads, such as 250 V a.c or 400 V to 600 V d.c Typically, film capacitors rated for d.c can withstand a.c peak voltages equal to their d.c rating for brief periods without failure To control the inductance of C S and its wiring for effective performance at 1 MHz, it may be necessary to connect two or three capacitors in parallel to ensure accuracy and frequency response.
Film capacitors with a capacitance of 0.1 µF and a voltage rating of 250 V a.c exhibit resonance around 3 MHz At 1 MHz, an error margin of approximately 3% may occur due to the inductance of these components To minimize inductive errors, capacitors with values lower than 0.1 µF can be connected in parallel.
Resistors R1, R2 and R3
Metal film resistors will give adequate performance under overload and at frequencies up to
1 MHz If overload capability is desired (see G.1.2), R1 and R2 should be rated 1 W.
Capacitors C1, C2 and C3
Extended foil construction film type capacitors are highly recommended, as their inductance remains stable and does not introduce significant errors up to 1 MHz Additionally, tolerance adjustments can be achieved by connecting multiple smaller capacitors in parallel.
Voltmeter
For full performance up to 1 MHz, the device used for measuring U 1 , U 2 , and U 3 should be a voltage measuring instrument which
– has an input resistance not less than 1 MΩ;
– has an input capacitance not more than 200 pF for a.c measurements;
– has a frequency range for a.c measurements from 15 Hz to 1 MHz, or more if higher frequencies are involved;
– has floating or differential input with common mode rejection of at least 40 dB up to
See Clause G.1 regarding the use of simpler instruments for particular applications.
Accuracy
The accuracy of the TOUCH CURRENT measuring network and its voltmeter is significantly affected by the precision of resistors and capacitors, as well as the voltmeter's frequency response and impedance Additionally, intercomponent capacitance and lead inductance play a crucial role in determining measurement accuracy.
The analysis reveals that the tolerances of the resistors R S and R B significantly impact the measured touch current in TOUCH CURRENT meter circuits, while the influence of other component tolerances is considerably less pronounced.
A voltmeter features both input resistance and input capacitance When measuring direct current (d.c.) or at low frequencies, a voltmeter with an input resistance of 1 MΩ will show a 1% lower reading due to voltage division with a 10,000 Ω resistor in the measuring network At high frequencies, the voltmeter's input capacitance becomes significant.
A 30 pF capacitor, when placed in parallel with the output capacitor of the measuring network, can lead to a measurement that is 0.15% lower in the network shown in Figure 4 and 0.33% lower in the network depicted in Figure 5.
Calibration and application of measuring instruments
NOTE A definition of calibration is to correlate the readings of an instrument with those of a standard in order to check the instrument
To evaluate the performance of a TOUCH CURRENT measuring network or instrument, it is essential to compare its readings with calculated ideal values across the relevant frequency range Documenting the measurement errors for multiple specimens of each instrument allows for the creation of error data compilations, which help establish guard bands for future measurements These guard bands indicate the expected range of measurement errors, and statistical confidence can be applied to their width In cases where only a single specimen of a specific instrument design is available, the actual error data can serve as the guard band.
The establishment of guard bands ensures that measurements can reproducibly indicate whether the EQUIPMENT being tested is within the TOUCH CURRENT limits, when used in the following way
For equipment manufacturers, it is essential to add a guard band to the readings and compare the sum to the limit, ensuring that equipment marked as compliant with the touch current limit is not rejected by testing laboratories Conversely, testing laboratories should subtract the guard band from the readings and compare the difference to the limit, preventing the rejection of equipment that genuinely meets compliance Additionally, the tolerances for instruments used in testing must be low enough to account for the difference between the limit value and the threshold of unwanted physiological effects, as outlined in IEC TS 60479-1.
If necessary, the guard band of a measuring network can be made narrower, for example by
– trimming of component values by connecting one or more components in parallel,
– minimizing lead length and sharp bends in leads (to reduce inductance),
– minimizing areas of parts in proximity (to reduce intercomponent capacitances)
Equipment manufacturers should aim to reduce TOUCH CURRENT levels, as designing equipment with current levels near the TOUCH CURRENT limit is regarded as poor practice This is due to the potential impacts of component tolerance, aging, usage, and environmental factors on performance.
TOUCH CURRENT When the TOUCH CURRENT from the EQUIPMENT is close to the limit value, special care should be taken in measurement precision and calibration of the test EQUIPMENT
If the TOUCH CURRENT is not close to the limit value, a wider guard band will be acceptable for instruments used by a manufacturer.
Records
Each measuring instrument must have established records that include periodic measurements of the measuring system These records are essential for future confirmation systems and for identifying any usage limitations.
informative) AC power distribution systems (see 5.4)
General
IEC 60364-1 classifies a.c power distribution systems into three categories: TN, TT, and IT, based on the arrangement of current-carrying conductors and earthing methods This annex provides detailed explanations of these classes and codes, along with examples illustrated in Figures I.1 to I.8, while noting that additional configurations may also be present.
– in most cases, the power systems apply for single-phase and three-phase EQUIPMENT but, for simplicity, only single-phase EQUIPMENT is illustrated;
– the power sources may be transformer secondaries, motor-driven generators or uninterruptible power systems;
– for transformers within a user’s building, some of the figures apply, and the building boundary represents a floor of the building;
– some power systems are earthed at additional points, for example at the power entry points of users’ buildings (see IEC 60364-4-41:2005)
The following types of EQUIPMENT connection are taken into account; the numbers of wires mentioned do not include conductors used exclusively for earthing:
The system codes used have the following meaning
– First letter: relationship of the power system to earth
• T means direct connection of one pole to earth;
• I means system isolated from earth, or one point connected to earth through an impedance
– Second letter: earthing of the EQUIPMENT
• T means direct electrical connection of the EQUIPMENT to earth, independently of the earthing of any point of the power system;
N refers to the direct electrical connection of the equipment to the earthed point of the power system In alternating current (a.c.) systems, this earthed point is typically the neutral point If a neutral point is not present, the connection may be made to a phase conductor.
– Subsequent letters, if any: arrangement of neutral and protective conductors
• S means the protective function is provided by a conductor separate from the neutral or from earthed line (or, in a.c systems, earthed phase) conductor;
• C means the neutral and protective functions are combined in a single conductor (PEN conductor).
TN power systems
TN power systems are directly earthed, the parts of the EQUIPMENT required to be earthed being connected by protective earthing conductors Three types of TN power systems are considered:
– TN-S power system: in which a separate protective conductor is used throughout the system;
– TN-C-S power system: in which neutral and protective functions are combined in a single conductor in part of the system;
– TN-C power system: in which neutral and protective functions are combined in a single conductor throughout the system
Some TN power systems utilize a secondary winding of a transformer with an earthed center tap (neutral) When both phase conductors and the neutral conductor are present, these systems are typically referred to as single-phase, 3-wire power systems.
Separate neutral and protective conductors
Figure I.1 – Examples of TN-S power system
The point at which the PEN conductor is separated into protective earth and neutral conductors may be at the building entrance or at distribution panels within the building
Figure I.2 – Example of TN-C-S power system
Neutral and protective functions combined in one conductor (PEN)
Figure I.3 – Example of TN-C power system
Protective and neutral functions combined in one conductor (PEN) This system is widely used in North America at 120/240 V
Figure I.4 – Example of single-phase, 3-wire TN-C power system
TT power systems
TT power systems feature a single point of direct earthing, where the necessary equipment is grounded at the user's location This grounding is achieved through earth electrodes that are electrically independent from the earth electrodes used in the power distribution system.
Earthed neutral and independent earthing of EQUIPMENT
Figure I.5 – Example of 3-line and neutral TT power system
Earthed line and independent earthing of EQUIPMENT
Figure I.6 – Example of 3-line TT power system
IT power systems
IT power systems typically remain isolated from the earth, with only one point potentially connected through an impedance or voltage limiter Essential equipment components are grounded to earth electrodes located at the user's premises.
The neutral may be connected to earth through an impedance or a voltage limiter, or isolated from earth
This system is commonly utilized in isolated configurations from the earth, particularly in various installations across France, where it operates at 230/400 V with impedance to earth Additionally, in Norway, it employs a voltage limiter with a non-distributed neutral at a line-to-line voltage of 230 V.
Figure I.7 – Example of 3-line (and neutral) IT power system
The system may be isolated from earth
Figure I.8 – Example of 3-line IT power system
Routine and periodic touch current tests, and tests after repair or modification of mains operated equipment
This annex outlines the methods and procedures for testing TOUCH CURRENT to ensure compliance with design requirements specified in the product standard These tests are conducted during production as routine checks, following any repairs or modifications, and at regular intervals throughout the product's usage.
The goal is to ensure that technicians or trained individuals conduct the test using straightforward methods to achieve adequate accuracy The results should be easily interpretable, and the measuring equipment must be cost-effective and user-friendly for practical field conditions.
Testing must be conducted following the specified procedures of this standard, utilizing the correct measuring network It is essential that these tests occur in suitable environmental conditions, whether in a field or factory setting.
The EQUIPMENT is to be tested in a stand-alone configuration without external connections, except for the mains supply
TOUCH CURRENT is to be measured and shall be at or below the limit defined in the EQUIPMENT standard as follows:
– if the limit is given as d.c current, measure the d.c and compare with the limit;
– if the limit is given in peak current, measure the peak current and compare with the peak limit;
– if the limit is given in r.m.s current, measure the r.m.s current and compare with the r.m.s limit
No routine or periodic test is required for ELECTRIC BURN currents unless specified by the
Network or instrument performance and initial calibration
The measured input impedance, defined as the ratio of input voltage to input current, and the transfer impedance, representing the output voltage to input current ratio, are evaluated against the ideal values derived from the nominal component specifications in Figures 3, 4, and 5 To ensure accurate measurements, the test equipment circuitry is meticulously arranged to minimize the impact of intercomponent capacitance, lead inductance, and the characteristics of the voltage measuring device on the voltage-current ratios.
Each instrument is assigned a guard band that reflects the measurement uncertainty across different frequencies If needed, the performance of measuring networks can be fine-tuned to reduce the width of this guard band.
NOTE 1 A definition of uncertainty of measurement is the characterization of the range within which the true value of a measurement is estimated to lie; this is a common term in metrology and calibration
NOTE 2 Guidance on adjusting the performance of measuring networks is given in G.4
The performance of a measuring network is evaluated by applying a variable frequency sinusoidal current to the instrument's input at test terminals A and B, as illustrated in Figures 3, 4, and 5 This process involves measuring the input current (I), input voltage (U), and output voltages (U₁, U₂).
Output voltage measurements are taken at different frequencies, ideally using the same voltmeter designated for all EQUIPMENT measurements related to product certification and confirmation procedures (refer to Clause K.2).
Table K.1 – Calculated input impedance and transfer impedance for unweighted touch current measuring network (Figure 3)
Frequency Input impedance Transfer impedance
Table K.2 – Calculated input impedance and transfer impedance for startle-reaction touch current measuring network (Figure 4)
Frequency Input impedance Transfer impedance
Table K.3 – Calculated input impedance and transfer impedance for letgo-immobilization current measuring network (Figure 5)
Frequency Input impedance Transfer impedance
Calibration in a confirmation system
Metrological confirmation, referred to as "confirmation" in this standard, encompasses a series of operations designed to verify that measuring equipment meets the necessary requirements for its intended use.
Each instrument that is used to determine acceptability for the purpose of certification of
Routine calibration of equipment is essential within a confirmation system to prevent performance drift beyond acceptable error limits It is important to reference the guard band and other data recorded during the initial calibration of the specific measuring instrument (refer to Clause K.1).
If a particular measuring instrument has drifted outside permissible limits, measurements made on the EQUIPMENT with that instrument since the last confirmation calibration shall be reviewed to check their validity
Calibration in a confirmation system is carried out in two steps
The d.c input resistance is measured and its value is checked against the ideal value
(2 000 Ω) and the value determined during initial calibration
This measurement protects against potential errors that may arise from simultaneous changes in input impedance and instrument response, ensuring that any additions or cancellations of errors are accounted for.
Input and output voltages, along with milliamperes indicated on the meter, are measured at various frequencies and compared to the data in Tables K.4, K.5, or K.6 Ideally, the output voltage should be measured using the same voltmeter designated for initial calibration and all subsequent measurements for product certification Measurements should be conducted at several frequencies across the entire range of interest, with particular focus on higher frequencies The input voltages must be selected to ensure output readings fall within the TOUCH CURRENT limit values for the measuring instrument, while also considering the power ratings of internal components.
Tables K.4, K.5, and K.6 are simplified versions of Tables K.1, K.2, and K.3, designed to streamline the confirmation process by eliminating the necessity to measure input current at high frequencies.
Table K.4 – Output voltage to input voltage ratios for unweighted touch current measuring network (Figure 3)
Frequency Output voltage to input voltage ratio Input voltage to output voltage ratio
Input voltage per milliampere indication
Table K.5 – Output voltage to input voltage ratios for startle-reaction measuring network (Figure 4)
Frequency Output voltage to input voltage ratio Input voltage to output voltage ratio
Input voltage per milliampere indication
Table K.6 – Output voltage to input voltage ratios for letgo-immobilization measuring network (Figure 5)
Frequency Output voltage to input voltage ratio Input voltage to output voltage ratio
Input voltage per milliampere indication
IEC 60050-195:1998, International Electrotechnical Vocabulary (IEV) – Part 195: Earthing and protection against electric shock
IEC 60050-604:1987, International Electrotechnical Vocabulary (IEV) – Chapter 604:
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IEC 60065, Audio, video and similar electronic apparatus – Safety requirements
IEC 60309-1:1999, Plugs, socket-outlets and couplers for industrial purposes – Part 1:
IEC 60335-1, Household and similar electrical appliances – Safety – Part 1: General requirements
IEC 60364-1, Low-voltage electrical installations – Part 1: Fundamental principles, assessment of general characteristics, definitions
IEC 60364-4-41:2005, Low-voltage electrical installations – Part 4-41: Protection for safety –
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