NEC 500.7(K)(2) and API RP500 6.5.2.e

[Natfuelbilll]

The NEC 500.7(K)(2) section permits unclassified equipment in a building located in a Class 1 Div 2 location. got it..


The API RP500 6.5.2.e section requires equipment "not suitable for division 2" to have power automatically disconnected at a detected LFL at 40%, or a detection malfuncunction. okay....


Is this API statement referring to the 500.7(K)(2) Code?

 

[bobgorno]

The NEC 500.7(K)(2) section permits unclassified equipment in a building located in a Class 1 Div 2 location. got it..

You need to carefully re-read 500.7(K)(2). It only applies to Div. 2 areas that do not contain a source of flammables. It is usually used for areas adjacent to, and with a shared opening (door) into a Div. 2 area containing flammables. Some examples are non-pressurized control rooms or eelectrical equipment rooms.

Use this with extreme care.....

API came first. NEC gas detection showed up a couple of code cycles ago.

 

[Natfuelbilll]

Then how does API RP500 6.5.2.e recommend equipment "not suitable for division 2" to be installed in the first place? Isn't installing not suitable equipment a NEC violation?

 

[bobgorno]

The 1991 version of API RP500 read "disconnect power from all electrical devices in the area that are not suitable for the area classificaiton without gas detectors".

In other words, all non-Div. 1 equipment would have to be disconnected. That was relaxed to a more sensible Div. 2 requirement.

The following note was also added in 1997 and R2002:
"Note: In the case of sensing 40 percent LFL or a gas detection system malfunction, corrective action to reduce the gas concentration should be initiated immediately."

Usually this means adding shutdowns of the gas in and out of a compressor building and and blowdowns of the compressor itself.

So, no where does it tell you you can put unclassified equipment in a hazardous area. The verbiage is not well stated.

 

[rbalex]

I have avoided responding to this thread. In the absence of a general standard such as NFPA 496, I don’t believe the NEC provides sufficient instruction or references for designing or inspecting gas detection schemes except in very limited cases. The reference in FPN No. 2 relates to 500.7(K)(1) and (K)(2), FPN 3 relates to 500.7 (K)(3).

It must also be recognized that Section 500.7 lists protection techniques rather than Electrical Area Classification criteria listed in Section 500.5 and other locations, such as Articles 511-516.

In the case of Sub-section 500.7(K), it is a protection technique with very limited applications. It specifically permits “…electrical equipment for unclassified locations…” in 500(K)(2) only.

I was on CMP14 when this protection technique was first recognized. If the applications weren’t so limited at the time, I would have voted against it. If you read my affirmative statement, you will see that I made a point that using 500.7(K) does not alter the electrical area classification; it simply permits the use of electrical equipment for reduced classifications under very specific conditions. The original Panel Action directed users to base designs on currently recognized national standards. That was changed by the TCC. I still don’t believe the NEC provides adequate direction.

The problem is that API RP500 does permit altering the classification.

Having said that, RP500 Sub-section 6.5.2.e still must be interpreted in the whole context of the opening statement of Section 6.5.2 which immediately refers back to Section 6.5.1. Section 6.5.1 has much more comprehensive design criteria than the NEC.

However, Sub-section 6.5.2.e applies both to 6.5.1.a and 6.5.1.b. In the first case (6.5.1.a), the installation should have been suitable for Division 2 anyway. It permits the continued use of the installation – even where “…electrical equipment for unclassified locations…” is permitted in Division 2 as long as all the other requirements of 6.5.2 are met.

In the second case (6.5.1.b), some “…electrical equipment for unclassified locations…” is permitted in Division 2, some is not.
In either case (6.5.1.a and 6.5.1.b), if “…electrical equipment for unclassified locations…” is part of the installation, a shutdown is required.

This recognizes that a Division 2 installation is adequate for some Division 1 locations for a short time.

 

[bobgorno]

BobA,

I remember how much you loved this subject from other past posts. Sorry for "baiting" you into this, knew you couldn't resist forever.

I felt bad that NatBill has been hangin out there on this. The wording and intent of NEC and API are truly perplexing. That's why my first response to the OP was to use care......

BobG