C1 D1 WW Wet Well

[tom baker]

a question came up in a class about wiring to a Wastewater Lift Station wet well, which is C1 D1. The installation uses RMC and sealoffs at the wet well for the conduit to the pumps, but changes to PVC and then runs to the control panel. An equipment grounding conductor is installed, bonded at each end. Is this allowed?

 

[rbalex]

Re: C1 D1 WW Wet Well

Tom,

Not quite, and without graphics its difficult to explain why. I'll try though.

I?m going to edit out some extraneous content in the first sentence of 501.16(A) and emphasize part of the second.

?bonding jumpers with proper fittings or other approved means of bonding shall be used. Such means of bonding shall apply to all intervening raceways, fittings, boxes, enclosures, and so forth between Class I locations and the point of grounding for service equipment or point of grounding of a separately derived system.

This applies to ??to all intervening raceways, fittings, boxes, enclosures, and so forth?? that are not themselves considered suitable to be EGCs, such as PVC.

As I believe you have described it, the EGC is not considered an adequate ?bond? for the PVC. Why? A ground-fault that may develop between energized conductors and the RMC is ?forced? to return to the source through the RMC/EGC bond in the Classified location. The ground-fault must then traverse all intervening, possibly ?loose,? joints in the RMC and each creates a potential ignition source in the Classified area. Now, depending on where the ground-fault occurs this may happen anyway of course, but a ?hard? bond across the PVC is considered necessary to minimize the probability.

Note: Read carefully, the exception actually emphasizes that the CMP wants the physically as well as electrically shortest possible ground-fault path.

I should clarify this is not necessarily my personal opinion of minimum ?good practice? but it seems to be the consensus of the Panel. This requirement is routinely overlooked with underground runs of PVC and there is no historical evidence of problems.


My personal concern would be the proper placement of the seals relative to the equipment and boundaries.

Edit: Corrected typo of 501.16(A) reference

[ April 15, 2005, 11:59 AM: Message edited by: rbalex ]

 

[friebel]

Re: C1 D1 WW Wet Well

Good morning Tom, I have looked at my Crouse-Hinds
Code-Digest and also the NEC and they both clearly state that in a Class 1, Division 1, Area you must use rigid metal conduit and/or intermediate metal conduit, having a taper of 3/4 inches per foot, and 5-threads fully engaged.
Code Reference: 500.8(D) and 501.10(A)(1)
So, with that being said, I would say that using PVC conduit is out.

 

[nhee]

Re: C1 D1 WW Wet Well

Tom,

I assume that the Control Panel and PVC conduit are in a non-hazardous area?

Bob,

Doesn't 501.4 (A)(1)(a)exception (along with sections of 514) allow PVC conduit to be installed with EGC in some instances? I recognize that these sections apply to UG installations, and that this particular case does not sound like an UG installation. But 501 is allowing an EGC to bond across a section of PVC within haz. area, isn't it?

 

[tom baker]

Re: C1 D1 WW Wet Well

Yes the control panel is in a non hazardous area.

 

[rbalex]

Re: C1 D1 WW Wet Well

Originally posted by nhee:
Tom,

I assume that the Control Panel and PVC conduit are in a non-hazardous area?

Bob,

Doesn't 501.4 (A)(1)(a)exception (along with sections of 514) allow PVC conduit to be installed with EGC in some instances? I recognize that these sections apply to UG installations, and that this particular case does not sound like an UG installation. But 501 is allowing an EGC to bond across a section of PVC within haz. area, isn't it?

I made the same assumption

nhee,

Yes it does. In fact, I was the originating author through API in the '99 Code to the 501.4 (A)(1)(a)exception and what was an exception but has become 501.4(A)(1)(c). Its an inconsistency. The "forced" ground path back through the hazardous area still occurs for UG systems. I've pointed it out to the CMP several times. They want to leave it be.

Edit add: and they want to retain the requirement as I described it for 501.16. That's the one I'd change but I can't quite get a handle on what the CMP would accept.

[ April 16, 2005, 08:03 PM: Message edited by: rbalex ]

 

[sirdle]

Re: C1 D1 WW Wet Well

rbalex,

As I understand you posts, you are saying that rigid metal conduit (RMC) IS an acceptable equipment grounding conductor (EGC), but that certain installations require that a bonding jumper be installed around loose fittings or around sections of the installation that are not electrically conductive.

It would seem that a bonding jumper installed around (through) the PVC would meet these requirements.

As long as the seals are properly installed and poured and the bonding jumpers are properly sized and bonded, I don't see why there should be a problem.

 

[rbalex]

Re: C1 D1 WW Wet Well

Sometimes I wish we could diagram sentences on this site. From my understanding, that skill is no longer taught in most schools anyway; so I must resort to extracting clauses and phrases and inserting parentheticals - hopefully without changing the essential meaning.

... Such means of bonding shall apply ... between [not in] Class I locations and the point of grounding for service equipment or point of grounding of a separately derived system.

The essence of this second sentence is that these are bonding requirements outside the Classified location. Otherwise, the sentence would not be needed at all.

If, "...the point of grounding for service equipment or point of grounding of a separately derived system" is already in the classified location (such as a lighting transformer) the presumption is that the approved wiring methods of 501.4, along with the specific requirements of 501.16, will automatically cover bonding issues located totally inside the classifed location.

Now, whether I personally think this should be necessary is a different issue.

Perhaps someone would care to submit a Proposal to the effect that a continuous equipment grounding conductor terminated both in the Classified location and at "...the point of grounding..." meets the intent of the second sentence.

 

[sirdle]

Re: C1 D1 WW Wet Well

Bob,

I am almost there. Please help me to understand. Are you saying that the installation as described in the original question was correct... except that it did not go far enough? That, in addition to the bonding jumper around the PVC, every other conduit connection (assuming the conduit was being used as an EGC) back to the point of bonding of the service equipment would also have to be bonded according to the requirements of 501.16?

Is it your interpretation that these bonding jumpers are required even when the conduit is not being used as an EGC, i.e., when an separate EGC is installed within the conduit?

Thanks, Rick

 

[rbalex]

Re: C1 D1 WW Wet Well

Rick,

What I understood Tom to describe was an installation where RMC was used in the Division 1 location. The boundary was established by the physical barrier of the wet-well?s top-cover; otherwise there would have to be a Division 2 somewhere also. A seal was at the boundary. From the seal to the control panel was a run of PVC.

Since the PVC is not an EGC itself, some other EGC must be established per the first sentence. We agree the internal EGC should be sufficient. Nevertheless, we are at odds with the text. (I don?t have to agree with it to say what it means.)

The text of the second sentence would want a bond run essentially from a ground fitting at the seal, across the PVC to another ground fitting at the control panel and likewise across any other intervening equipment that was not itself a suitable EGC. This applies only to the system outside the classified location.

The exception permits this to be stopped, for example, in a muitibuilding facility where one of the buildings is fed from another per 250.32(A), (B), and (C). But the emphasis is the shortest possible physical ground fault path to the system grounding electrode conductor. A low impedance path to the GEC is not considered alone sufficient.

The current CMP may be a bit more open to revising the text. But I doubt it. Most of them were there when they rejected the idea the ?parallel? in 501.16(B) meant ?electrically connected at both ends? rather than ?physically parallel? as shown in the current NEC Handbook.