Intrinsic vs Wiring Method

[Moistness]

I have been scouring the latest National Electric Code as well as the internet and am unclear of the answer to this question and hope that the people of this form can help. I am looking for chapter and verse from the National Electrical Code or any code standard.


If you follow article 501.10 (a) of the National Electric Code for Class 1 Division 1 conduit, seals, and wiring, and if your instrumentation meets the requirements of article 501.105 (a).

Are you required to add an intrinsically safe barrier, say from a PLC panel that is in an unclassified area to say a pressure transmitter that is in a class 1 div 1 area and is rated for a class 1 div 1 area along with all the conduit and wire properly installed?

I am struggling to find the answer and hoping you all could help.

I do understand that if the customer requires a barrier, you add one, but I’m more interested if the customer is silent on the matter.

 

[rbalex]

See Article 504 first. All of it.

Ultimately, you will need barriers (and boundary seals) in the installation you have described.

 

[Moistness]

rbalex,
I appreciate the resonance and read Article 504. All of it.
Suppose the pressure transmitter in my example is explosion-proof, rated for class 1 div 1, and has the proper seal ahead of the unit. Do you still need the I.S. barrier?

 

[rbalex]

You are either using an Intrinsically Safe (IS) System [Article 504] and don't need an explosionproof enclosure but do need an IS barrier or IS power supply or you are using a “conventional” Class I, Division 1 wiring method [Section 501(A)] and don't need an IS barrier or power supply.

IS barriers or power supplies are only required for Intrinsically Safe Systems. Modified IS sealing is still required under 504.70.

 

[Moistness]

Thank you.
I came from a coal industry background and probably did things a little overkill, also MESA requires a higher standard in some cases than the NEC requires. I have a new position that mainly deals in the gas industry now and I am finding they do things a little differently.
I appreciate your time.

 

[rbalex]

I'm more familiar with the MSHA acronym. It is more comprehensive than the NEC since it covers more than electrical applications, but I didn't find it to be a “higher standard” than NEC Article 502 with respect to Classified locations for coal dust.

Thank you.
I came from a coal industry background and probably did things a little overkill, also MESA requires a higher standard in some cases than the NEC requires. I have a new position that mainly deals in the gas industry now and I am finding they do things a little differently.
I appreciate your time.

Class I is indeed different than Class II. See Section 502.5 as a good example. Sealing requirements are also significantly different. The reason is that gas and vapor behavior is different from dusts.

In Class I, absent a protection technique [Section 500.8] like pressurization or hermetic sealing, gases and vapors will still enter explosionproof enclosures, seals alone can't exclude them.

In Class Il, seals are often unnecessary. There are several effective techniques to exclude dusts from the interior of enclosures - including “good housekeeping”.

IS is an entirely different method that attempts to remove the ignition source rather than the fuel from the fire triangle. However, IS still requires special attention to seals and grounding/bonding in Classified locations.

 

[Strathead]

IS is an entirely different method that attempts to remove the ignition source rather than the fuel from the fire triangle. However, IS still requires special attention to seals and grounding/bonding in Classified locations.

rbalex probably got tired of typing... The sealing grounding and bonding is to prevent the gases from coming in to contact with other ignition sources. Such as seeping out of the classified area and igniting. or unbonded metal creating a spark.