Explosion proof equipment

[cppoly]

Is equipment in Class I Division II required to be explosion proof or is that only Class I Division I?

 

[petersonra]

Explosion proof is just one means of explosion protection. Depending on your situation, it is possible that certain types of things may need to be explosion proof in a division 2 area. However, not everything in a division 1 area has to be explosion proof either.

 

[cppoly]

Where could I find the requirements of what equipment is required to be explosion proof based upon the Class and Division?

 

[Elect117]

The NEC would be a decent place to start. Chapter 5 starts with it and then there are some specifics sprinkled through out depending on occupancies. I would start, however, with what gas it is and see if there are any other NFPA related documents as well. Sometimes they are more clear to the chemical or element you are working with.

 

[tom baker]

Take a look at section 500.4 for having a classification document available. This would be your first step and will guide you on the required wiring methods. Guessing on what is required can be expensive.

 

[don_resqcapt19]

Is equipment in Class I Division II required to be explosion proof or is that only Class I Division I?

If the enclosure contains an arc producing device, it needs to be explosion proof or hermetically sealed. A good place to start is 501.10.
(A) is for Division 1 and (B) for Division 2.

 

[cppoly]

After looking more into Chapter 500 (using the 2008 NEC), I am now more confused than ever

Some follows ups and general questions related to a Class I Division II location:

I couldn’t find a definition of arc-producing equipment but it looks like all equipment in the informational note in 500.8(B)(1) are potential sources of ignition (Luminaires and other heat-producing apparatus, Switches, Circuit breakers, Plugs and Receptacles). 500.8(B)(1) indicates that this equipment is to be identified for use in the specific hazardous location.

For reference, 500.8(B)(1) Approval for Class and Properties:

Equipment shall be identified not only for the class of location but also for the explosive, combustible, or ignitible properties of the specific gas, vapor, dust, or fibers/flyings that will be present. In addition, Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor. Class II equipment shall not have an external temperature higher than that specified in 500.8(D)(2). Class III equipment shall not exceed the maximum surface temperatures specified in 503.5.

Question: Just verifying that all luminaires, switches, circuit breakers, plugs and receptacles potential sources of ignition? Also, any ideas why motors aren’t mentioned?

Question: I don’t see HVAC equipment mentioned. If the equipment is outside of a hazardous area but has ductwork inside a hazardous area (which draws air back into the equipment), could there be a potential for an explosion at the equipment?


Going onto 500.8(C) Marking, it indicates:

Equipment shall be marked to show the environment for which it has been evaluated. Unless otherwise specified or allowed in (C)(6), the marking shall include the information specified in (C)(1) through (C)(5):

(1) Class. The marking shall specify the class(es) for which the equipment is suitable.
(2) Division. The marking shall specify the division if the equipment is suitable for Division 2 only. Equipment suitable for Division 1 shall be permitted to omit the division marking.
(3) Material Classification Group. The marking shall specify the applicable material classification group(s) in accordance with 500.6.
(4) Equipment Temperature. The marking shall specify the temperature class or operating temperature at a 40°C ambient temperature, or at the higher ambient temperature if the equipment is rated and marked for an ambient temperature of greater than 40°C. The temperature class, if provided, shall be indicated using the temperature class (T Codes) shown in Table 500.8(C). Equipment for Class I and Class II shall be marked with the maximum safe operating temperature, as determined by simultaneous exposure to the combinations of Class I and Class II conditions.
(5) Ambient Temperature Range. For equipment rated for a temperature range other than –25°C to +40°C, the marking shall specify the special range of ambient temperatures in degrees Celsius. The marking shall include either the symbol “Ta” or “Tamb.”

And in 500.8(C)(6) Special Allowances it indicates:

(a) General-Purpose Equipment. Fixed general-purpose equipment in Class I locations, other than fixed luminaires, that is acceptable for use in Class I, Division 2 locations shall not be required to be marked with the class, division, group, temperature class, or ambient temperature range.

Question: I can’t find a definition of “General-Purpose Equipment”. What is this referring to in 500.8(C)(6)?

Question: It looks like Luminaires in a Class I Division II area is required to be marked with the Class, Division, Group, Equipment Temperature, and Ambient Temperature range – is that correct?

Question: It looks like in a Class I Division I area, all luminaires, switches, circuit breakers, plugs and receptacles are required to be marked with the Class, Division, Group, Equipment Temperature, and Ambient Temperature range – correct?


In Looking at 500.7 Protection Techniques:

(A) Explosionproof Apparatus. This protection technique shall be permitted for equipment in Class I, Division 1 or 2 locations.
(B) Dust Ignitionproof. This protection technique shall be permitted for equipment in Class II, Division 1 or 2 locations.
(C) Dusttight. This protection technique shall be permitted for equipment in Class II, Division 2 or Class III, Division 1 or 2 locations.
(D) Purged and Pressurized. This protection technique shall be permitted for equipment in any hazardous (classified) location for which it is identified.
(E) Intrinsic Safety. This protection technique shall be permitted for equipment in Class I, Division 1 or 2; or Class II, Division 1 or 2; or Class III, Division 1 or 2 locations.
(F) Nonincendive Circuit. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.
(G) Nonincendive Equipment. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.
(H) Nonincendive Component. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.
(I) Oil Immersion. This protection technique shall be permitted for current-interrupting contacts in Class I, Division 2 locations as described in 501.115(B)(1)(2).
(J) Hermetically Sealed. This protection technique shall be permitted for equipment in Class I, Division 2; Class II, Division 2; or Class III, Division 1 or 2 locations.
(K) Combustible Gas Detection System. A combustible gas detection system shall be permitted as a means of protection in industrial establishments with restricted public access and where the conditions of maintenance

Question: It looks like that lighting fixtures in a Class I Division II area are required to either be explosion proof or hermetically sealed for all practical purposes. I don’t think the other protection techniques are practical or apply. Thoughts?

 

[don_resqcapt19]

...
I couldn’t find a definition of arc-producing equipment but it looks like all equipment in the informational note in 500.8(B)(1) are potential sources of ignition (Luminaires and other heat-producing apparatus, Switches, Circuit breakers, Plugs and Receptacles). 500.8(B)(1) indicates that this equipment is to be identified for use in the specific hazardous location.

Heat producing devices are not arc producing devices. Things that interrupt the flow of current such as circuit breakers, switches, relay contacts and others are arc producing devices and are required to be in an explosionproof enclosure where installed in a Class I, Division 2 location.

For reference, 500.8(B)(1) Approval for Class and Properties:

Equipment shall be identified not only for the class of location but also for the explosive, combustible, or ignitible properties of the specific gas, vapor, dust, or fibers/flyings that will be present. In addition, Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor. Class II equipment shall not have an external temperature higher than that specified in 500.8(D)(2). Class III equipment shall not exceed the maximum surface temperatures specified in 503.5.

There are maximum surface temperature rules for equipment installed in all three Classes. The maximum permitted surface temperature for equipment that is installed in a Class II location is often lower than that for a Class I location because the hazard, combustible dust, is in direct contact with the heat producing equipment and exposure to heat, over time can actually lower the ignition temperature of the combustible dust.
In general the maximum surface temperature for a Class I location is 80% of the auto ignition temperature of the flammable gas. This temperature can be high. For example gasoline vapors have an autoignition temperature between 477° and 536°F. That would permit the equipment to have a surface temperature of 380°F requiring the use of equipment with a temperature code of 3A or higher. (the maximum temperature goes down as the temperature code goes up)

Question: Just verifying that all luminaires, switches, circuit breakers, plugs and receptacles potential sources of ignition? Also, any ideas why motors aren’t mentioned?

Yes those are all potential sources of ignition, but in general, luminaires are not required to be explosionproof in a Class I, Division 2 location.
Motors are covered in 501.125 and where installed in a Class I, Division 1 location must be explosionproof or use one of the other protections found in list items (2) through (4) of 501.125(A). The most common application for three motors in a Class I, Division 2 location is 501.125(B)(3) as those motors do not have any arc producing contacts. Most single phase motors have some type of a starting contact and would be required to be explosionproof where installed in a Class I, Division 2 location.

Question: I don’t see HVAC equipment mentioned. If the equipment is outside of a hazardous area but has ductwork inside a hazardous area (which draws air back into the equipment), could there be a potential for an explosion at the equipment?"

If the duct work is transporting the flammable gas as the electrical equipment is in the air flow, than that equipment would have to be suitable for the Class and Division. In most cases, the electrical equipment is not in the air flow and would not be in the classified area.
This points out the importance of the area classification documents required by 500.4. No electrical installation associated with a classified area should be started without having the area classification documents in your possession.

Going onto 500.8(C) Marking, it indicates:

Equipment shall be marked to show the environment for which it has been evaluated. Unless otherwise specified or allowed in (C)(6), the marking shall include the information specified in (C)(1) through (C)(5):
...
And in 500.8(C)(6) Special Allowances it indicates:

(a) General-Purpose Equipment. Fixed general-purpose equipment in Class I locations, other than fixed luminaires, that is acceptable for use in Class I, Division 2 locations shall not be required to be marked with the class, division, group, temperature class, or ambient temperature range.

Question: I can’t find a definition of “General-Purpose Equipment”. What is this referring to in 500.8(C)(6)?

Things like conduit bodies, junctions boxes, conduit unions, and things like that, used in a Division 2 area do not need any markings or identification.

Question: It looks like Luminaires in a Class I Division II area is required to be marked with the Class, Division, Group, Equipment Temperature, and Ambient Temperature range – is that correct?

Yes, they must have those markings for use in a Class I, Division 2 location.

Question: It looks like in a Class I Division I area, all luminaires, switches, circuit breakers, plugs and receptacles are required to be marked with the Class, Division, Group, Equipment Temperature, and Ambient Temperature range – correct?

I think only the luminaires have an equipment temperature marking, but all of the other markings are required. Note that the ambient temperature can be an issue with outside explosionproof enclosures as they need a special marking if the ambient will be below 13°F.

In Looking at 500.7 Protection Techniques:

....

Question: It looks like that lighting fixtures in a Class I Division II area are required to either be explosion proof or hermetically sealed for all practical purposes. I don’t think the other protection techniques are practical or apply. Thoughts?

Hermetically sealed applies to equipment that has an arc producing device. Hermetic seals can be used in a Division 2 location in lieu of an explosionproof enclosure.
For luminaires you need to look at 501.130(B), and in general they only need a temperature marking.

Most of the real rules for Class I locations are found in Article 501, and that is where you should be looking. The information in Article 500 is more general, and the specific rules for Class I, II, and III are found in Articles 501, 502, and 503 respectively.

Note that any code references I have cited are from the 2023 NEC.

Note I deleted some original text to get under the 1000 character limit.

 

[cppoly]

Yes those are all potential sources of ignition, but in general, luminaires are not required to be explosionproof in a Class I, Division 2 location.
Motors are covered in 501.125 and where installed in a Class I, Division 1 location must be explosionproof or use one of the other protections found in list items (2) through (4) of 501.125(A). The most common application for three motors in a Class I, Division 2 location is 501.125(B)(3) as those motors do not have any arc producing contacts. Most single phase motors have some type of a starting contact and would be required to be explosionproof where installed in a Class I, Division 2 location.

Don, thanks for your replies, they were very helpful. Can you elaborate on lighting fixtures in Class I Division II not requiring to be explosion proof and is there a code section I could look at? Looking at the protection techniques in 500.7, it would appear this section applies to all electronic equipment in a classified area. I would think lighting fixtures are considered electronic equipment and would have to be explosion proof or am I missing something?

For luminaires you need to look at 501.130(B), and in general they only need a temperature marking.

Thanks for 501.130(B)

Most of the real rules for Class I locations are found in Article 501, and that is where you should be looking. The information in Article 500 is more general, and the specific rules for Class I, II, and III are found in Articles 501, 502, and 503 respectively.

In trying to figure out if explosion proof fixtures are required in a Class I Division II and following the work flow of looking at Article 500 first for general requirements and Article 501 for more specific requirements, it doesn't really say much in section 501.130(B) about lighting fixtures. I would think the explosion proof protection requirements are better defined in Article 500 and not Article 501 - or no?

 

[don_resqcapt19]

Don, thanks for your replies, they were very helpful. Can you elaborate on lighting fixtures in Class I Division II not requiring to be explosion proof and is there a code section I could look at? Looking at the protection techniques in 500.7, it would appear this section applies to all electronic equipment in a classified area. I would think lighting fixtures are considered electronic equipment and would have to be explosion proof or am I missing something?



Thanks for 501.130(B)



In trying to figure out if explosion proof fixtures are required in a Class I Division II and following the work flow of looking at Article 500 first for general requirements and Article 501 for more specific requirements, it doesn't really say much in section 501.130(B) about lighting fixtures. I would think the explosion proof protection requirements are better defined in Article 500 and not Article 501 - or no?

The rules are in Article 501, not 500. The rules in 501.130(B) tell you everything you need to know for a Division 2 luminaire.

For a Division 2 location, the only real requirements are that the surface temperature of the lamp not exceed 80% of the autoignition temperature of the flammable gas and the luminaire not have any arc producing contacts. If the temperature of the surface of the lamp will exceed 80% of the autoignition temperature, or if there are arc producing contacts, you need an explosionproof luminaire.

In the past, the surface temperature of many lamps would exceed the 80% value, but few LEDs would do that.

So you have to determine the normal operating surface temperature of the lamps in the luminaire, and verify there are no switches or other arc producing contacts in the luminaire.