Purged and pressurized motors for zones and divisions

NEC Article 505.5 B2 Definition for Zone 1 A class I zone 1 location is a location 1 in which ignitable concentrations of flamma-ble gases or vapors are likely to exist under normal oper

Are they the same?

B Y B H A R A T M I S T R Y & W I L L I A M G L A W R E N C E

many years These motors operate in hazard-ous (classified) locations where an explosive gas or vapor atmosphere is likely to be present in a normal

operation Motors operating in this area require special

pro-tection against igniting the explosive gas or vapor To

oper-ate these motors safely, special protections such as the purged

and pressurized technique or the explosion-proof enclosure are required The large fabricated frame motors are typically protected by the purged and pressurized technique

Zone 1 or division 1 hazardous (classified) locations have been defined to be essentially the same in National Fire Pro-tection Association (NFPA) 70 [1], National Electrical Code (NEC), C22.1 [2], Canadian Electrical Code (CEC), and inter-national standards [Interinter-national Electrotechnical Commission (IEC)] The petroleum and chemical facility environments for IEC/NEC/CEC zone 1 and NEC/CEC division 1 are not Digital Object Identifier 10.1109/MIAS.2009.935589

20

different, yet the safety requirements

and how the motors are used in these

areas are addressed from competing

vantage points The codes and standards

are transcending national barriers in an

attempt to synchronize, without

sacri-ficing safety requirements; however,

there are still diverging regulations

These diverging requirements are

dis-cussed later

Fabricated induction and brushless

synchronous machines are larger than

National Electric Manufacturing

Asso-ciation (NEMA) frame sizes and

manu-factured to order in voltages 2.3 kV

and above They are designed and built

to suit specific applications, operating

under detailed load conditions and for

the petroleum and chemical process

in-dustries located within hazardous

(clas-sified) areas under the local authority

having jurisdiction (LAHJ or AHJ)

The population of these motors

oper-ating in zone 1 or division 1 areas is

around 10% or less The design and application of these

motors are very important because they operate in

hazard-ous areas where ignitable gas could be present at any time

during normal operation

For division 1 locations, both the U.S and Canadian

installation standards refer to the NFPA 496 [5] standard

for requirements for purged and pressurized enclosures

Comparatively, for zone 1 locations, IEC standard 60079-0

[3] for general requirement and IEC standard 60079-2 [4]

for pressurized enclosure (p) are applicable Both the U.S

adoption [American National Standards

Institute/Interna-tional Society of Automation (ANSI/ISA 60079-2)] [13]

and the Canadian adoption (E60079-2) [14] of the IEC

standard have very few national differences and, for the

pur-pose of this article, are considered nearly identical

The standards discussed herein are not limited to motors;

they are applied equally to induction and synchronous

gen-erators as well as machine accessories installed in hazardous

locations The term motor used herein should be considered

applicable to all rotating electrical machines

Although the North American and the international

standard-development groups are working to improve their

own documents, there is an ongoing effort to harmonize or

reduce conflicts and confusion Despite this work, the fact is

that the LAHJ is responsible for establishing which single

set of codes and regulations apply to the project: either the

NEC or IEC philosophy is chosen On the drawing board,

there are a few mechanical differences between the two

Electrically, the components are the same but output

charac-teristics (e.g., torques and other tolerances not discussed

here) vary These differences are mainly due to the extra

safety rules adopted to satisfy individual national standards

and/or installation codes and occasional features learned from

application experience

In addition to the NEC and CEC, the IEC 60079-14

standard [6], Electrical Installations in Hazardous Areas (Other

Than Mines), provides additional information on the

selec-tion of the apparatus for use in zone 1 This standard [6]

allows the use of type p protection (pres-surized enclosure) in zone 1 area, com-plying with the IEC 60079-2 standard

This article outlines the key area of design, construction, and testing of large fabricated frame motors selected for zone 1 and division 1 hazardous areas protected by pressurization

Hazardous Areas NEC and CEC definitions for division 1 and zone 1 are almost identical and are also substantially equivalent to the IEC 60079-10 [7] zone 1 locations It can

be seen from the definitions of both division 1 and zone 1 locations that these are locations where the explosive at-mosphere may exist frequently under normal operation

For division 1 locations where the explosive atmosphere exists continuously under normal operation (these would be defined as zone 0 under the zone classifi-cation system), motors would not be usually installed in such area based on the guidance given

in the NEC and CEC

This article compares the applications in zone 1 and the portions of division 1 where motors are likely to be installed and used

Compare the following excerpts

NEC Article 500.5(B)(1) Definition for Division 1

A class I division 1 location is a location 1) in which ignitable concentrations of flammable gases, flammable liquid-produced vapors, or com-bustible liquid-produced vapors can exist under normal operating conditions or

2) in which ignitable concentrations of such flammable gases, flammable liquid-produced vapors, or combustible liquids above their flash points may exist frequently because of repair or maintenance operations or because of leakage or 3) in which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases, flammable produced vapors, or combustible liquid-produced vapors and might also cause simulta-neous failure of electrical equipment in such a way as to directly cause the electrical equipment

to become a source of ignition

NEC Article 505.5 (B)(2) Definition for Zone 1

A class I zone 1 location is a location 1) in which ignitable concentrations of flamma-ble gases or vapors are likely to exist under normal operating conditions or

2) in which ignitable concentrations of flammable gases or vapors may exist frequently because of repair or maintenance operations or because of leakage or

3) in which equipment is operated or processes are carried on, of such a nature that equipment

THE ENCLOSURE VOLUME FOR MOTORS IS DEFINED AS THE VOLUME WITHIN THE ENCLOSURE MINUS THE VOLUME OF THE INTERNAL COMPONENTS PLUS VOLUME

OF ROTOR.

21

breakdown or faulty oper-ations could result in the release of ignitable con-centrations of flammable gases or vapors and also cause simultaneous failure

of electrical equipment in

a mode to cause the elec-trical equipment to become

a source of ignition or 4) that is adjacent to a class

I, zone 0 location from which ignitable concentra-tions of vapors could be communicated unless com-munication is prevented

by an adequate positive-pressure ventilation from

a source of clean air and effective safeguards against ventilation failure are provided

CEC Rule J18-006(a) Definition for Division 1

Division 1 consists of a class I locations in which

explosive gas atmospheres are likely to be present

continuously, intermittently, or periodically during

normal operation

CEC Rule 18-006(b)(i) Definition for Zone 1

Zone 1 consists of a class I location in which 1)

explo-sive gas atmospheres are likely to occur in normal

operation or 2) the location is adjacent to a class I,

zone 0 location, from which explosive gas

atmos-pheres could be communicated

IEC 60079-10: Clause 2.5.2 Definition for Zone 1

A place in which an explosive atmosphere consisting

of a mixture with air of flammable substances in the

form of gas, vapor, or mist is likely to occur in normal

operation occasionally

NEC Approach

General Consideration

NEC Section 500.2 Definition for Purging and Pressurization

The process of 1) purging, supplying an enclosure with

a protective gas at a sufficient flow and positive

pres-sure to reduce the concentration of any flammable gas

or vapor initially present to an acceptable level and 2)

pressurization, supplying an enclosure with a

protec-tive gas with or without continuous flow at sufficient

pressure to prevent the entrance of a flammable gas

Under the fine print note (FPN), it says for further

information see ANSI/NFPA 496-2003, Purged and

Pressurized Enclosures for Electrical Equipment

NEC section 501.125(A)(2) provides the requirement

for motors operating in class I division 1 The second

para-graph of this section states that motors may be of

the totally enclosed type supplied with positive

pres-sure ventilation from a source of clean air with

dis-charge to a safe area, so arranged to prevent energizing

of the machine, until ventilation has been established

and the enclosure has been purged with at least ten volume of air and also arranged to automatically dee-nergize the equipment when the air supply fails

The external surface temperature of such a motor must not exceed in any case 80% of the ignition temperature

of the gas or vapor involved Appropri-ate devices shall be provided to detect and automatically deenergize the motor

or provide an adequate alarm if there

is any increase in the temperature of the motor beyond design limits All auxiliary equipments shall be of a type identified for the location in which it

is installed

Design, Construction, and Testing

As noted earlier, the second paragraph of 501.125(A) does not address design issues, construction methods, or testing

of purged and pressurized motors The FPN of NEC sec-tion 500.2 says to refer to ANSI/NFPA 496 to find those design requirements

NFPA 496 was originally developed as two parts The first part was addressed in 1967 for purged enclosures for electrical equipment in class I hazardous (classified) loca-tions The second part then followed with purged enclo-sures for class II hazardous (classified) locations in 1970 The last revision of 2003 has major changes to align the document with the latest NFPA style and also with per-mission to use methods other than a timer to ensure that the purging process has removed any flammables The design, construction, and testing requirements of NFPA 496 [5] for motors are discussed further

General Requirements for Pressurized Enclosure

There are three types of pressurization systems defined in the standard

the protected enclosure from division 1 or zone 1 to unclassified

the protected enclosure from division 1 to division

2 or zone 1 to zone 2

the protected enclosure from division 2 or zone 2 to unclassified

The enclosure volume for motors is also defined as the volume within the enclosure minus the volume of the inter-nal components, e.g., rotors, stators, and field coils

Requirements of Pressurized Enclosure for Class I Location

The following are the requirements of pressurized enclo-sure for class I location

likely to be damaged under the conditions to which

it may be subjected A typical pressurized motor en-closure is shown in Figure 1(a)

of the protective gas supply A typical pressurization

THE IEC APPROACH IS MORE DESCRIPTIVE AND DEFINITIVE RATHER THAN SPECIFYING THE DESIGN REQUIREMENTS.

22

system is shown in Figure 2, which can protect the

enclosure from excessive pressure

the enclosure from excessive pressure in the case of a

control failure A typical location of such a device is

shown in Figure 1(b)

pre-vent the discharge of ignition-capable particles to a

division 1 location

enclosure outlet shall be to an unclassified location,

unless the outlet is designed to prevent the discharge

of ignition-capable particles during normal operation

be installed as close as practical but not more than

18 in from the pressurized enclosure

main-tain the required positive pressure, the enclosure shall

be purged before reenergizing

to allow free airflow through the enclosure

inside the pressurized enclosure after purging

adjacent enclosures connected to the main enclosure

shall be considered separately, and protection shall

be provided accordingly as explained later

shall be purged in series or shall be purged separately

main enclosure by nonrestricted top and bottom vents that are common to the main enclosure

with a minimum vent size of 6.3 mm (one-fourth inch) diameter

adjacent enclosure shall be protected by other means (e.g., explosion proof, intrinsic safety, hermetic seal-ing, nonincendive, encapsulation, and so forth) All typical devices and boxes are shown in Figure 3

Pressurization System

positive pressure of at least 25 Pa (0.1 in of water) above the surrounding atmosphere during the oper-ation of protected equipment

protective gas supply to maintain required pressure

in type Y and type Z pressurization

3

A typical division 1 motor.

2

Pressurization system.

Equipotential Jumper Cables

(a)

(b) Relief Device

1

(a) Pressurized motor enclosure without a heat exchanger.

All pressurization system

com-ponents that may be energized

in the absence of protective gas

shall be approved for the

classi-fied location in which they are

installed A typical pressurization

system is shown in Figure 2

Protective Gas System

nitrogen, or other nonflammable

gas shall be permitted as a

protec-tive gas

unclassified location

for type Y and type Z pressurization until at least

ten volumes of purging gas have passed through

the enclosure while maintaining an internal

pres-sure of at least 25 Pa (0.1 in of water) The time

for ten-volume change out and the required

purg-ing gas volume is specified by the manufacturer

electrical equipment in type X pressurizing until

at least ten volumes of purging gas have passed

through the enclosure while maintaining an

inter-nal pressure of at least 25 Pa (0.1 in of water)

electrical circuits for the enclosures that can be

readily opened without the use of a key or special

tool in type X pressurization The interlock shall

be approved for the external area classification

requir-ing a cooldown period shall be designed to require

the use of a special key or tool for opening

Determining of Temperature Class Marking

The temperature class (T code) marked on the enclosure

shall represent (under normal operating conditions) the

highest of the following:

1) the hottest enclosure external surface temperature

2) the hottest internal component surface temperature,

e.g., surface temperature of winding space heaters

3) the temperature of the protecting gas leaving the

enclosure

Wiring Practices and Auxiliary Equipments

The external wiring for all auxiliary devices is typically

provided in rigid metal conduit, although other wiring

methods suitable for the area may be used All connectors,

elbows, and T joints in rigid conduit runs are required to

be approved for the location Conduit seals are provided

near the protected enclosure, within 18 in, and at the entry

of explosion-proof boxes, as shown in Figure 3 The main

power terminal box employs a series-pressurization system

All auxiliary devices must be approved for the location

As a good practice, bonding jumpers across the various

components in a multisectioned enclosure are typically

provided Doing so achieves equal potential across all parts

and mitigates the risk of ignition because of high-energy

discharge A photograph of a typical equipotential jumper

is shown in Figure 1

Testing

NFPA 496 does not specify specific type tests or routine tests to validate the design criteria stated earlier How-ever, it is a common practice for manu-facturers to validate each design function during the witness of third-party in-spection or as required by the local authorities

The following tests are typically re-quired by third-party inspectors or local authorities as a minimum to validate the design criteria:

1) functional tests or checks of pressurization system 2) the overpressure test of pressurized enclosures 3) the leakage test of pressurized enclosures to ensure the leakage is kept to the minimum or less than the allowable maximum limit of the pressurization system 4) the temperature class determination by running the heat run of motor and/or winding space heaters The temperature class for the large fabricated frame motor is generally determined from the maximum surface temperature of winding space heaters, which typically run hotter than the stator winding or rotor

Markings

speci-fied in the clause 4.11 of NFPA 496

division 1

temperature in degree Celsius

IEC Approach

General Consideration

IEC has prepared the 60079 series of standards for electri-cal equipment used in an explosive gas atmosphere IEC standard 60079-0 provides the general guidelines required for motors designed for hazardous areas IEC standard 60079-2 provides the specific requirement for purged and pressurized enclosures, p type of protection The following paragraphs will refer to both standards

The IEC approach is more descriptive and definitive rather than specifying the design requirements IEC 60079-2 speci-fies the requirements of the protected motor enclosure, safety control devices, and design validation by tests

The last revision in the year of 2007, IEC 60079-2 standard, introduced the equipment protection levels (EPLs)

to establish the relative risk of the product becoming a source of ignition The following three EPLs are defined in the standard for electric equipments designed for gas group

II, explosive gas atmospheres

having a very high level of protection, which is not

a source of ignition in normal operation, during expected malfunctions, or during rare malfunctions

It is typically provided in zone 0 explosive gas atmos-pheres and cannot be achieved using pressurization

having a high level of protection, which is not a

THE PURGE TIME VERIFICATION IS THE MOST CHALLENGING AND EXPENSIVE TEST TO PERFORM.

24

source of ignition in normal operation or during

expected malfunctions It is typically provided in

zone 1 explosive gas atmospheres and can be achieved

by px and py types of protection

having an enhanced level of protection, which is

not a source of ignition in normal operation and

which may have some additional protection to ensure

that it remains inactive as an ignition source It is

typically provided in zone 2 explosive gas

atmos-pheres and can be achieved by pz type of protection

Design, Construction, and Testing

Design and construction are very similar to NEC, with

minor changes as highlighted later

Construction Requirements of Pressurized Enclosure

The NEC protection methods used in the division system,

type X, type Y, and type Z pressurization, are designated as

px, py, and pz types of protection, respectively, in IEC

60079-2 standard for the zone system The definition of

these three types of protection are similar to those in the

NEC for the division system

However, the definition of enclosure volume in IEC

60079-2 is not the same as in NEC It is defined as follows:

Enclosure volume is a volume of the empty enclosure

without internal apparatus The free internal volume

of the rotating electrical machines is the volume of

enclosure without internal apparatus plus the volume

displaced by the rotor

A few more requirements over and above the NEC [1]

for pressurized enclosure are specified later:

that the enclosure, including ducts, if any, withstand

1.5 times the maximum overpressure specified by

the manufacturer for normal service, with all outlets

closed with a minimum of 200 Pa

compartment in such a way that an effective

purg-ing is ensured A well-designed manifold system

provided in the enclosure will help to provide

effec-tive purging A typical manifold system is shown in

Figure 4 The internal partitions are also considered

in design to avoid dead pockets

main enclosure or be separately purged If they are

6.3 mm diameter are provided for adequate purging

maintained by any installed cable glands or conduits

If the cable glands or

con-duits are not sealed, they

have to be considered as part

of the pressurized enclosure

A quick summary of the types

of protection for IEC/zones is

pro-vided in Table 1

Temperature Class Determination

The temperature class is

deter-mined based on the hottest surface

temperature of the internal or external component of motor

As was the case with divisions, it is typically determined from the operating surface temperature of winding space heaters, which can often run hotter than the stator or rotor

In a type px-pressurized enclosure, the internal compo-nent temperature may exceed the marked temperature class

if the time period sufficient to permit the component to cool

to the marked temperature class is specified Appropriate measures shall be taken to prevent, if pressurization ceases, any explosive gas atmosphere, which may exist making con-tact with the hot component surface before it has cooled below the permitted maximum value The maximum per-mitted value of each temperature class is provided in the IEC 60079-0 [3] standard This type of protection is typi-cally provided in motors operating in zone 1 area

In a type py enclosure, hot ignition-capable parts in nor-mal operation are not permitted inside the enclosure This type of protection is generally provided for instrumenta-tion operating in zone 1 areas

In a type pz enclosure, the temperature class shall be based on the hottest external surface of the enclosure This type of protection is typically provided to motors operating

in zone 2 area

Safety Provisions and Safety Devices for Hazardous Area

Safety provisions are discussed later for the type px-protected motors operating in zone 1 hazardous area A typical pressur-ization system shown in Figure 2 has all the safety devices

The following are the minimum key design criteria for

px protection

to operate when the pressurized enclosure overpressure

4

Internal manifold system.

TABLE 1 DETERMINATION OF PROTECTION TYPE.

Flammable Substance in Motor Enclosure

External Area Classification

Enclosure Contains Ignition-Capable Apparatus

Enclosure Does Not Contain Ignition-Capable Apparatus

25

falls below the minimum value.

The minimum overpressure for px

or py is 50 Pa and for pz is 25 Pa

This overpressure shall be

main-tained relative to the external

pressure at every point within the

pressurized enclosure

to prevent electrical equipment

within a pressurized enclosure

from becoming energized until

purging has been completed

op-eration of the safety devices for px

pressurization shall be as follows:

1) following the initiation of

the sequence, the purging flow through and the overpressure in the pressurized enclosure shall be monitored; purging flow will

be as specified by the manufacturer, and the mini-mum overpressure of 50 Pa shall be monitored 2) the purging timer can be started after achieving

minimum flow rate and overpressure, as speci-fied by the manufacturer

3) after finishing purge time, the internal protected

electrical equipment can then be energized 4) the circuit shall be arranged to reset to the

begin-ning in the event of the failure of any step in the sequence

supply to an electrical equipment if door or covers of

motor can be opened without the use of a tool or key

from exceeding maximum design pressure when

the regulator fails This is required for the

com-pressed air system used for pressurization

Purging Criteria and Media for px Pressurization

The minimum purge flow and time is based upon a

five-enclosure-volume change out It is determined from the test

or from the calculation by inspection authority The

manu-facturer shall specify the minimum purge flow and time

based on the specified test criteria provided in the standard

Air of normal instrument quality, nitrogen, or other nonflammable gas is considered acceptable as a protective gas Typically, clean instrument air is used in motors for purging and pres-surization The protective gas

the inlet of the enclosure

Wiring Practices and Auxiliary Equipments

The wiring practice is different for motors installed in accordance with IEC 60079-14 [6] In an IEC-based in-stallation, the typical installation employs cable and cable glands at the terminal boxes of the pressurized enclosure However, in accordance with IEC 60079-14, wiring with conduit and appropriate seals, although unusual, are equally acceptable

All other accessories shall be suitably protected for the location The auxiliary boxes with terminals are typically Ex e [7] (increased safety) installed with cable and cable glands

As in the NEC installation, equipotential bonding cable jumpers are provided in large fabricated frame motors to avoid the potential of arcing or sparking across metal enclosures

Testing to Validate Design

IEC 60079-2 requires type tests and routine tests to be per-formed on a pressurized enclosure to validate the design criteria as specified in the standard

Type tests as specified in the standard are as follows:

is 1.5 times design pressure

leak-age rate of the pressurized enclosure

(heav-ier than air) and helium (lighter than air) test gases

px enclosure This test shall be performed stopping the motor and running at its maximum speed Pres-sure is likely to be meaPres-sured at the lowest presPres-sure point in an enclosure

internal pressure in the case of regulator failure of safety device This is required only when the enclo-sure is designed for use with compressed air and where leakage vents or pressure-relief devices are relied upon to limit the maximum overpressure when a regulator fails

Routine test specified in the standard are as follows:

The validations of the earlier tests are very expensive, extensive, and time consuming These tests require setting

up of a completely assembled motor on the test floor to per-form all tests (typically during a third-party witness) Out

of all those tests, the purge time verification is the most challenging and expensive test to perform

A typical test setup for the purge time verification with argon and helium gases of 18-MW, 30-pole, 10-kV, 50-Hz, synchronous motor is shown in Figure 5

5

Motor test setup for purge verification test.

BONDING JUMPERS ACROSS THE VARIOUS COMPONENTS

IN A MULTISECTIONED ENCLOSURE ARE PROVIDED.

26

The results of the purge time being verified with argon

and helium gases on a few motors are provided in Table 2

The Annexure A of the standard 60079-2 [4] was followed

for the purge time verification methods

The last 8,430-kW four-pole motor was the first

pres-surized enclosure motor tested with gases Since then, the

other two motors have an improved manifold system and

an internal enclosure design The first two motors in the

table have come very close to the minimum required purge

time; however, the quoted purge time provided to the

customer is increased for the additional safety factor over

the life of the motor

The purge time verified with gases has a major impact

on how the internal manifold system has been designed

and confirming that there is no blocking of the airflow to

create dead pockets for hazardous gas The data in Table 2

also shows the longer purge time verified from the argon

gas test

Conclusions

The design, construction, and application requirements for

purged and pressurized motors are very similar in both

NEC and IEC standards other than a few differences

dis-cussed in the article The wiring practices for the North

American and IEC worlds are generally conduit based and

cable based, respectively; however, both wiring methods

are accepted in both systems Despite those similarities (and

wiring practice differences), there is no direct replacement of

motor built for either system

The purging time required by NFPA 496 has a good

safety margin by requiring the ten-volume air exchanges

and, thus, may not require verification by argon or helium

gases In contrast, the IEC-calculated purge time may not

be enough based on a five-volume air exchange The purge

time based on a five-volume air exchange may be good for

a smaller size enclosure; however, it has to be looked at

carefully in determining purge time for the large

fabri-cated frame motors when the verifying test has not been

performed with argon and helium test gases A motor

designed to meet the performance requirements of the

IEC will not likely qualify to meet the purge time

require-ment of NEC

The safety of the people working in either division 1 or

zone 1 hazardous (classified) locations and the protection of

the facility is a prime concern Worldwide, LAHJ has the

legal authority to mandate the specific codes or standards

to be applied to assure safety and protection Two parallel ap-proaches, North American NEC/ CEC and international IEC sys-tems, address the requirements for the equipment installed in these locations Although essen-tially equal, the two systems are not interchangeable, and it is the obligation of the purchaser to advise which specific codes and/or standards are appropriate for the specific installation and what (if any) third-party certification is required It is the responsibility of the purchaser or user to satisfy the legal requirements of the AHJ

Acknowledgments The authors acknowledge Mr Jason Ball, Ms Brennan Orr, and other colleagues for reviewing this article and pro-viding their valuable input

References

[1] National Electrical Code (NEC), 2008 [Also known as National Fire Protection Association, NFPA 70].

[2] Canadian Electrical Code (CEC) Part 1, Canadian Standards Association C22.1-06, 2006.

[3] Explosive Atmospheres—Part 0: Equipment—General Requirements, Inter-national Electrotechnical Commission (IEC) IEC 60079-0, 2007.

[4] Explosive Atmospheres—Part 2: Equipment—Protection by Pressurized Enclosure “p,” International Electrotechnical Commission (IEC) IEC 60079-2, 2007.

[5] NFPA 496: Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2003.

[6] Electric Apparatus for Explosive Gas Atmospheres—Part 14: Electrical Installations in Hazardous Areas (Other Than Mines), International Elec-trotechnical Commission (IEC) IEC 60079-14, 2002.

[7] Electric Apparatus for Explosive Gas Atmospheres—Part 10: Classification

of Hazardous Areas, International Electrotechnical Commission (IEC) IEC 60079-10, 2002.

[8] Explosive Atmospheres—Part 7: Equipment Protection by Increased Safety “e,” International Electrotechnical Commission (IEC) IEC 60079-7, 2006.

[9] Rotating Electric Machines, Part 1: Rating and Performance, International Electrotechnical Commission (IEC) IEC 60034-1, 2004.

[10] B Mistry and D Somma, “Which motor would you choose for your hazardous area? Type n, e or p!” in Proc Petroleum and Chemical Indus-try Conf., PCIC 2006-22, Philadelphia, PA, 2006, pp 1–10.

[11] J Gardner and F Dixon, “Purged and pressurized systems for class 1, div 1 & 2, and zone 1 & 2 hazardous locations,” in Proc Petroleum and Chemical Industry Conf., PCIC 2006-26, Philadelphia, PA, 2006,

pp 1–7.

[12] D295 Super Mini Purge Manual ML360.

[13] Electrical Apparatus for Explosive Gas Atmospheres—Part 2 Pressurization

“p,” ANSI/ISA 60079-2, 2004.

[14] Electrical Apparatus for Explosive Gas Atmospheres—Part 2 Pressurization

“p,” CAN/CSA-E60079-2, 2002 (re-affirmed 2006).

Bharat Mistry (bharat.mistry@ge.com) is with General Elec-tric Canada in Peterborough, Ontario William G Lawrence is with FM Approvals in Norwood, Massachusetts Mistry is a Mem-ber of the IEEE Lawrence is a Senior MemMem-ber of the IEEE This article first appeared as “Purged and Pressurized Motors Made to IEC/NEC/CEC Zone 1 (EX P) and to NEC/CEC Division

1 (Type X): Are They the Same?” at the 2007 Petroleum and Chemical Industry Conference

TABLE 2 EXAMPLE OF PURGE TIMES.

kW/Pole

Expected Five-Volume Change Purge Time (min)

Verified Purge Time with Argon Gas (min)

Verified Purged Time with Helium Gas (min)

Quoted Purge Time (min)

27