De-rating Class 1, Div II areas.

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elk3730

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I'm looking for an exception in the NEC to de-rate a Class 1, Div II area. I've understood that all equipment/instrumentation can be de-rated to "non-hazardous" within a 25' sphere of an open flame (i.e. = natural gas pilot in operation).

Where is this exception explained within the NEC - Article 500?

Also, is this exception acceptable under IEC - ATEX standards?

Industrial Example: Subistute a NEMA 4 enclosure in place of NEMA 7 within this 25' sphere.
 

petersonra

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Location
Northern illinois
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engineer
elk3730 said:
I'm looking for an exception in the NEC to de-rate a Class 1, Div II area. I've understood that all equipment/instrumentation can be de-rated to "non-hazardous" within a 25' sphere of an open flame (i.e. = natural gas pilot in operation).

Where is this exception explained within the NEC - Article 500?

Also, is this exception acceptable under IEC - ATEX standards?

Industrial Example: Subistute a NEMA 4 enclosure in place of NEMA 7 within this 25' sphere.
It would seem sort of silly to classify an area where there was open flame.
 

elk3730

Member
Refineries

Refineries

Refineries have numerous areas within the facility that carry a Class 1, Div II classifications. These areas can be de-rated & re-zoned if a new installation will have an open flame in the operating process.

I'm just looking for the NEC exception that covers this 25' sphere. If you know where I can find that exception in the NEC, I would appreciate your input.

Your last post contains no technical merit - only your opinion. I'm looking for technical data to back up this exception.
 

don_resqcapt19

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Location
Illinois
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retired electrician
The NEC does not tell you how to classify areas...it only tells you how to wire the area after it has been classified based on other documents. There is NFPA 497, and the API (American Petroleum Institute)RP 500 among others. Look at the FPNs after 500.4(B).
Don
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
elk3730 said:
Refineries have numerous areas within the facility that carry a Class 1, Div II classifications. These areas can be de-rated & re-zoned if a new installation will have an open flame in the operating process.

I'm just looking for the NEC exception that covers this 25' sphere. If you know where I can find that exception in the NEC, I would appreciate your input.

Your last post contains no technical merit - only your opinion. I'm looking for technical data to back up this exception.
I think you missed the point entirely. I don't see how you can have an open flame in a classified area. So putting an open flame in the area would not magically make it unclassified.

You would probably have to take steps first to make the area unclassified so that you could put an open flame in that area.

In any case, the open flame is not premises wiring so is not covered under the NEC.
 
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rbalex

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Location
Mission Viejo, CA
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Professional Electrical Engineer
There has never been a defined distance for the application you mention. NFPA 497, Section 5.4.3 states:

Open flames and hot surfaces associated with the operation of certain equipment, such as boilers and fired heaters, provide inherent thermal ignition sources. Electrical classification is not appropriate in the immediate vicinity of these facilities. However, it is prudent to avoid installing electrical equipment that could be a primary ignition source for potential leak sources in pumps, valves, and so forth, or in waste product and fuel feed lines.
I prefer the current API statement:
6.2.4.3The practice of not classifying locations where non-electrical ignition sources (e.g., the open flame of an unprotected fired vessel or flare tip) exist has been utilized in previous issues of RP 500. It is recommended that the application of this practice be limited to unprotected fired vessels or flare tips and that the resulting unclassified locations be restricted to their immediate vicinity. Electrical equipment located in these unclassified locations typically is de-energized for the majority of the time that the flame source is not present.

Note: Although from a practical view, when an open flame is present, a spark from electrical equipment in the immediate area of the flame would not likely be the initiator of combustion, the location of sources of ignition is not a criteria for the classification of locations. Classification is, by definition, based on the likelihood of the presence of flammable mixtures. It is not the intent of this document to recommend the creation of an unclassified location in which one can locate general purpose electrical devices that are not directly associated with the combustion or ignition systems of unprotected fired vessels or flare tips.
In reality, an open flame can only create a boundary. I pretty much wrote the original API ?Note.?
 

elk3730

Member
Thank you

Thank you

Thank you for the information & technicial reference. That's excatly what I was looking for.
 
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