Cable in conduit in Class 1 Division 1

[Willowleaf]

I am having a fruitless argument with the electrical engineers in my department over conductors and cables for Class 1 Div 1 installation (they are designing a large ethane cracking plant). I'm an electrician who knows the NEC (passed both the exam for electrician years ago and the BOCA electrical inspectors exams) and have done countless XP installations in manufacturing plants and tank farms. I was also a factory rep for a while for OZ Gedney, Crouse Hinds and Carol Cable. Per the wording of Section 501.10(A)(1)(a) as long as you have a proper threaded conduit installation (with all the requisite seals and fittings) you can use ANY conductor or cable installed within that raceway. In fact we most often pulled THHN and blue hose in our raceway systems in classified locations. I told them that you could technically pull Romex in the conduit system if the plant specs allowed it.

But these engineers seem to think there has to be some explicit wording in the NEC stating that cables that will be wholly contained within a conduit system do not need to be explicitly "approved" for Class 1 Div 1. They confuse the sections in 501.10 describing the limited cable types for EXPOSED cabling installations with those cables also being required when enclosed in a conduit system. So they think that the only cables that they can pull in conduit in C1D1 areas are those called out for exposed cable installation. Yep, try to pull MI cable in rigid conduit, guys, I dare ya.

I've provided them with a couple of answers from this forum supporting my understanding but they keep asking "where does it say this is OK in the NEC?" They will not accept my explanation that, by default, if you install an= C1D1 approved raceway system you can install ANY type of cable in it that would meet standards in the rest of the plant outside the classified area.

Can anyone offer a Code reference that can help me convince these guys what those of us who install these systems have always known?

 

[MasterTheNEC]

I am having a fruitless argument with the electrical engineers in my department over conductors and cables for Class 1 Div 1 installation (they are designing a large ethane cracking plant). I'm an electrician who knows the NEC (passed both the exam for electrician years ago and the BOCA electrical inspectors exams) and have done countless XP installations in manufacturing plants and tank farms. I was also a factory rep for a while for OZ Gedney, Crouse Hinds and Carol Cable. Per the wording of Section 501.10(A)(1)(a) as long as you have a proper threaded conduit installation (with all the requisite seals and fittings) you can use ANY conductor or cable installed within that raceway. In fact we most often pulled THHN and blue hose in our raceway systems in classified locations. I told them that you could technically pull Romex in the conduit system if the plant specs allowed it.

But these engineers seem to think there has to be some explicit wording in the NEC stating that cables that will be wholly contained within a conduit system do not need to be explicitly "approved" for Class 1 Div 1. They confuse the sections in 501.10 describing the limited cable types for EXPOSED cabling installations with those cables also being required when enclosed in a conduit system. So they think that the only cables that they can pull in conduit in C1D1 areas are those called out for exposed cable installation. Yep, try to pull MI cable in rigid conduit, guys, I dare ya.

I've provided them with a couple of answers from this forum supporting my understanding but they keep asking "where does it say this is OK in the NEC?" They will not accept my explanation that, by default, if you install an= C1D1 approved raceway system you can install ANY type of cable in it that would meet standards in the rest of the plant outside the classified area.

Can anyone offer a Code reference that can help me convince these guys what those of us who install these systems have always known?

Well I am not sure I want to get into this debate...but I will say this. The only thing that Section 501.10(A)(1) is speaking to is the wiring method that are permitted for use in a Class 1, Division 1 location. It is not speaking to the conductors that are to be installed within the wiring method. In their argument it they would have to say that the NEC depicts the type of conductor and insulation to be installed in said raceway and nothing of that is mentioned. Case in point, the use of Type MC-HL is permitted where used as defined in Section 501.10(A)(1(c)...but it mentions nothing in regards to the conductors in the cable method being mentioned...they could be THHN/THWN-2 or XHHW or XHHW-2 and so on.

My point is this, the internal conductors generally have no bearing on the actual wiring method that IS permitted which is actually limited to RMC,IMC,MI under the general use and of course Type MC-HL and ITC-HL for industrial establishments.

However it sounds like in order to win any portion of this argument, regardless if I agree with the "any cable" portion of the statement, you should formulate your question and submit it to the NFPA for an informal interpretation as that would have more weight that any statement from this forum (in my opinion in case those who feel offended say so). You would still have to meet the securing and supporting requirements of the applicable cable being installed (like Type NM-B you mentioned) and if the raceway you are talking about is not specifically for physical damage protection (which it is not...you are installing it to meet Section 501.10(A)(1)) then you would need to meet the securing and supporting requirements of that specific article.....it's not the can I install it in a raceway that is the tricky part...it's how you intend to terminate it that becomes the problem.

Also in terms of seal offs and so on.......you have this little thing called Section 501.10(C) to contend with.....so I would argue that Type NM-B Cable is not permitted based on it's intended use and in accordance with UL 719. In other words the seals....seal the deal....on that option and again why on earth would you every use Type NM-B for that...but alas I know it was just an example you proposed....and we can agree to disagree on that one.

 

[Willowleaf]

yes, the NM-B cable was not a serious suggestion, just underlining my point

yes, the NM-B cable was not a serious suggestion, just underlining my point

in fairness to the two engineers who are involved in this discussion, they do get my point: that it is the raceway/sealing system or cable jacket themselves that have to be approved for C1D1, not the conductors within them. Having worked as a factory rep for a major cable manufacturer I know that cables themselves are not manufacturer rated for classified locations. It is the way they are installed that creates their NEC acceptability in those locations. But the engineers' problem is in explaining to others (such as plant managers or even other engineers) where in the NEC this understanding is specifically expressed or implied. Just as certain cables are rated for dry or wet locations or for higher ambient temperatures, apparently they think that they should also be specifically designated as acceptable for classified locations. My argument is that it goes without saying that if they are not specifically excluded by the NEC then they are acceptable. The NEC is ponderous enough. If they had to delineate EVERY possible default exception we would need to put the next edition on wheels to haul it around.

My premise (and this is also the premise of the NEC) is that when you properly install a threaded conduit raceway system with approved seals, XP junction boxes, etc., in which to contain and suppress the buildup of naturally occurring ignition events in a C1D1 atmosphere, then you have effectively created an isolated environment in which standard building materials may be used. In fact I used the example of XP toggle switch units which have the machined gas-cooling connection surfaces built into the enclosure and cover. But the actual switch that activates within the component is just a standard industrial grade snap switch with no specific rating for C1D1. It becomes acceptable for C1D1 due to the enclosure and raceway system that contain the ignition events that may occur during the contact of the switch due to the atmosphere. XP does not "prevent" combustive events, it contains and mitigates their effect.

 

[petersonra]

I don't think this is all that hard.

501.10(A) lists what wiring methods can be used in a CID1 area.

Rigid metal conduit is one of the wiring methods allowed. We look in 344 for how RMC is used.

344.22 specifically allows cables to be installed in RMC if not otherwise prohibited.

 

[MasterTheNEC]

My premise (and this is also the premise of the NEC) is that when you properly install a threaded conduit raceway system with approved seals, XP junction boxes, etc., in which to contain and suppress the buildup of naturally occurring ignition events in a C1D1 atmosphere, then you have effectively created an isolated environment in which standard building materials may be used.

Agree 100% with that statement