5.3.1 Protection against overload and abnormal operation
Equipment shall be so designed that the risk of fire or electric shock due to mechanical or electrical overload or failure, or due to abnormal operation or careless use, is limited as far as practicable.
After abnormal operation or a single fault (see 1.4.14), the equipment shall remain safe for an
OPERATOR in the meaning of this standard, but it is not required that the equipment should still be in full working order. It is permitted to use fusible links, THERMAL CUT-OUTS, overcurrent protection devices and the like to provide adequate protection.
Compliance is checked by inspection and by the tests of 5.3. Before the start of each test, it is checked that the equipment is operating normally.
If a component or subassembly is so enclosed that short-circuiting or disconnection as specified in 5.3 is not practicable or is difficult to perform without damaging the equipment, it is permitted to make the tests on sample parts provided with special connecting leads. If this is not possible or not practical, the component or subassembly as a whole shall pass the tests.
Equipment is tested by applying any condition that may be expected in normal use and foreseeable misuse.
In addition, equipment that is provided with a protective covering, is tested with the covering in place under normal idling conditions until steady conditions are established.
Table 5C – Test voltages for electric strength tests based on required withstand voltages
REQUIRED WITHSTAND VOLTAGE
up to and including kV peak
Test voltage for BASIC INSULATION or SUPPLEMENTARY
INSULATION
Test voltage for REINFORCED INSULATION
kV peak a.c. or d.c.
0,33 0,33 0,5
0,5 0,5 0,8
0,8 0,8 1,5
1,5 1,5 2,5
2,5 2,5 4
4,0 4 6
6,0 6 8
8,0 8 12
12 12 18
U a U 1,5 x U
Linear interpolation is permitted between the nearest two points.
If FUNCTIONAL INSULATION is tested (as required by 5.3.4 b), the test voltage for a WORKING VOLTAGE up to and including 42,4 V peak or 60 V d.c. shall not exceed 707 V peak or d.c. For a higher WORKING VOLTAGE, the test voltage given in Table 5B or Table 5C is used.
a U is any REQUIRED WITHSTAND VOLTAGE higher than 12,0 kV.
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5.3.2 Motors
Under overload, locked rotor and other abnormal conditions, motors shall not create a hazard due to excessive temperatures.
NOTE Methods of achieving this include the following:
– the use of motors that do not overheat under locked-rotor conditions (protection by inherent or external impedance);
– the use in SECONDARY CIRCUITS of motors that may exceed the permitted temperature limits but that do not create a hazard;
– the use of a device responsive to motor current;
– the use of an integral THERMAL CUT-OUT;
– the use of a sensing circuit that disconnects power from the motor in a sufficiently short time to prevent overheating if, for example, the motor fails to perform its intended function.
Compliance is checked by the applicable test of Annex B.
5.3.3 Transformers
Transformers shall be protected against overload, for example, by
− overcurrent protection,
− internal THERMAL CUT-OUTS, or
− use of current limiting transformers.
Compliance is checked by the applicable tests of Clause C.1.
5.3.4 Functional insulation
For FUNCTIONAL INSULATION, CLEARANCES and CREEPAGE DISTANCES shall satisfy one of the following requirements a) or b) or c).
For insulation between a SECONDARY CIRCUIT and an inaccessible conductive part that is earthed for functional reasons, CLEARANCES and CREEPAGE DISTANCES shall satisfy a) or b) or c).
a) They meet the CLEARANCE and CREEPAGE DISTANCE requirements for FUNCTIONAL INSULATION in 2.10 (or Annex G).
b) They withstand the electric strength tests for FUNCTIONAL INSULATION in 5.2.2.
c) They are short-circuited where a short-circuit could cause
• overheating of any material creating a risk of fire, unless the material that could be overheated is of V-1 CLASS MATERIAL, or
• thermal damage to BASIC INSULATION, SUPPLEMENTARY INSULATION or REINFORCED INSULATION, thereby creating a risk of electric shock.
Compliance criteria for 5.3.4 c) are in 5.3.9.
5.3.5 Electromechanical components
Where a hazard is likely to occur, electromechanical components other than motors are checked for compliance with 5.3.1 by applying the following conditions:
– mechanical movement shall be locked in the most disadvantageous position while the component is energized normally; and
– in the case of a component that is normally energized intermittently, a fault shall be simulated in the drive circuit to cause continuous energizing of the component.
The duration of each test shall be as follows:
– for equipment or components whose failure to operate is not evident to the OPERATOR: as long as necessary to establish steady conditions or up to the interruption of the circuit due to other consequences of the simulated fault condition, whichever is the shorter; and – for other equipment and components: 5 min or up to interruption of the circuit due to a
failure of the component (for example, burn-out) or to other consequences of the simulated fault condition, whichever is the shorter.
For compliance criteria see 5.3.9.
5.3.6 Audio amplifiers in information technology equipment
Equipment having audio amplifiers shall be tested in accordance with 4.3.4 and 4.3.5 of IEC 60065. The equipment shall be operating normally before the tests are conducted.
5.3.7 Simulation of faults
For components and circuits other than those covered by 5.3.2, 5.3.3, 5.3.5 and 5.3.6, compliance is checked by simulating single fault conditions (see 1.4.14).
Note deleted
The following faults are simulated.
a) Short-circuit or disconnection of any components inPRIMARY CIRCUITS.
b) Short-circuit or disconnection of any components where failure could adversely affect
SUPPLEMENTARY INSULATION or REINFORCED INSULATION.
c) Short-circuit, disconnection or overloading of all relevant components and parts unless they comply with the requirements of 4.7.3.
NOTE 2 An overload condition is any condition between NORMAL LOAD and maximum current condition up to short-circuit.
d) Faults arising from connection of the most unfavourable load impedance to terminals and connectors that deliver power from the equipment, other than mains power outlets.
e) Other single faults specified in 1.4.14.
Where there are multiple outlets having the same internal circuitry, the test is only made on one sample outlet.
For components in PRIMARY CIRCUITS associated with the mains input, such as the supply cord, appliance couplers, EMC filtering components, switches and their interconnecting wiring, no fault is simulated, provided that the component complies with 5.3.4 a) or 5.3.4 b).
NOTE 3 Such components are still subject to other requirements of this standard where applicable, including 1.5.1, 2.10.5, 4.7.3 and 5.2.2.
In addition to the compliance criteria given in 5.3.9, temperatures in the transformer supplying the component under test shall not exceed those specified in Clause C.1, and account shall be taken of the exception detailed in Clause C.1 regarding transformers that would require replacement.
5.3.8 Unattended equipment
Equipment intended for unattended use and having THERMOSTATS, TEMPERATURE LIMITERS and
THERMAL CUT-OUTS, or having a capacitor not protected by a fuse or the like connected in parallel with the contacts, is subjected to the following tests.
THERMOSTATS, TEMPERATURE LIMITERS and THERMAL CUT-OUTS are also assessed for compliance with the requirements in Clause K.6.
Equipment is operated under the conditions specified in 4.5.2 and any control that serves to limit the temperature is short-circuited. If the equipment is provided with more than one
THERMOSTAT, TEMPERATURE LIMITER orTHERMAL CUT-OUT, each is short-circuited, one at a time.
If interruption of the current does not occur, the equipment is switched off as soon as steady conditions are established and is permitted to cool down to approximately room temperature.
For equipment not intended for continuous operation, the test is repeated until the temperature has stabilized, regardless of any marking of RATED OPERATING TIME or RATED RESTING TIME. For this test the THERMOSTATS, TEMPERATURE LIMITERS and THERMAL CUT-OUTS
are not short-circuited.
If in any test a MANUAL RESET THERMAL CUT-OUT operates, or if the current is otherwise interrupted before the temperature has stabilized, the heating period is taken to have ended;
but if the interruption is due to the rupture of an intentionally weak part, the test is repeated on a second sample. Both samples shall comply with the conditions specified in 5.3.9.
5.3.9 Compliance criteria for abnormal operating and fault conditions 5.3.9.1 During the tests
During the tests of 5.3.4 c), 5.3.5, 5.3.7, 5.3.8 and Clause C.1:
− if a fire occurs, it shall not propagate beyond the equipment; and
− the equipment shall not emit molten metal; and
− ENCLOSURES shall not deform in such a way as to cause non-compliance with 2.1.1, 2.6.1, 2.10.3 (or Annex G) and 4.4.1.
Moreover, during the tests of 5.3.7 c), unless otherwise specified, the temperatures of insulating materials other than thermoplastic materials shall not exceed those in Table 5D.
EN 60950-1:2006+A12:2011 (E)
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Table 5D – Temperature limits for overload conditions
Maximum temperature °C Thermal class
105 (A) 120 (E) 130 (B) 155 (F) 180 (H) 200 220 250
150 165 175 200 225 245 265 295
The designations A to H, formerly assigned in IEC 60085 to thermal classes 105 to 180, are given in parentheses.
If the failure of the insulation would not result in HAZARDOUS VOLTAGES or HAZARDOUS ENERGY LEVELS becoming accessible, a maximum temperature of 300 °C is permitted. Higher temperatures are permitted for insulation made of glass or ceramic material.
5.3.9.2 After the tests
After the tests of 5.3.4 c), 5.3.5, 5.3.7 and 5.3.8 and Clause C.1, an electric strength test according to 5.2.2 is made on:
− REINFORCED INSULATION; and
− BASIC INSULATION or SUPPLEMENTARY INSULATION forming part ofDOUBLE INSULATION; and
− BASIC INSULATION between the PRIMARY CIRCUIT and the main protective earthing terminal;
if any of the following applies:
− the CLEARANCE or CREEPAGE DISTANCEhas been reduced below the value specified in 2.10 (or Annex G); or
− the insulation shows visible signs of damage; or
− the insulation cannot be inspected.
6 Connection to telecommunication networks
If the equipment is to be connected to a TELECOMMUNICATION NETWORK, the requirements of Clause 6 apply in addition to the requirements of Clauses 1 to 5 in this standard.
NOTE 1 It is assumed that adequate measures according to ITU-T Recommendation K.11 have been taken to reduce the likelihood that the overvoltages presented to the equipment exceed 1,5 kV peak. In installations where overvoltages presented to the equipment may exceed 1,5 kV peak, additional measures such as surge suppression may be necessary.
Note deleted
NOTE 3 The requirements of 2.3.2, 6.1.2 and 6.2 can apply to the same physical insulation or CLEARANCE. NOTE 4 The AC MAINS SUPPLY system, if used as a communication transmission medium, is not a TELECOMMUNICATION NETWORK (see 1.2.13.8), and Clause 6 does not apply. The other clauses of this standard will apply to coupling components, such as signal transformers, connected between the mains and other circuitry. The requirements for DOUBLE INSULATION or REINFORCED INSULATION will generally apply. See also IEC 60664-1 and Annex Z of this standard for overvoltages to be expected at various points in the AC MAINS SUPPLY system.
Note deleted