C1 D1 Location GRC to PVC

Status
Not open for further replies.
tom baker

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
Question came to me on the following:
"We have a Class 1 Div 1 sewer wet well with 4 GRC raceway's leaving it going into another vault where we have the seal-off's, it changes from GRC to PVC at that point and then still under ground stubs up to our control panel. For the Bonding question, the contractor I am talking about ran a 1 inch pvc pipe from the control panel underground to the seal off vault and bonded to the 4 raceways. Do the GRC raceways have to be bonded at both end or is one fine and does this sound like an appropriate installation to you?? "

My answer:
The NEC requires the electrical continuity of the ...raceways in hazardous locations to be per the methods in 250.92(B)(2) to B 4 and essentially this means RMC from the haz location to the source. See 250.100 The method the contractor used does not comply with 250.100. The 2005 NEC clarified that even with a supplemental EGC, the bonding in 250.92 is required.

Whats the opinion of the forum? The AHJ says the installation is OK.
 
250.100 Bonding in Hazardous (Classified) Locations.
Regardless of the voltage of the electrical system, the electrical
continuity of non?current-carrying metal parts of
equipment, raceways, and other enclosures in any hazardous
(classified) location as defined in Article 500 shall be ensured
by any of the methods specified in 250.92(B)(2) through
(B)(4) that are approved for the wiring method used. One or
more of these bonding methods shall be used whether or not
supplementary equipment grounding conductors are installed.
Click to expand...

Inside the classified area he met the requirements. This paragraph clearly states you only have to meet the requirements of 250.92(B)(2)-(4) inside the classified area.
 
Bob,
What about 501.30(A)?
501.30(A)(A) Bonding The locknut-bushing and double-locknut types of contacts shall not be depended on for bonding purposes, but 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.
Click to expand...
Don
 
I first read the op last night but I was just too tired to think straight and couldn?t build the mental picture of the installation. I confess I?m still a bit confused.

I am assuming that there was a single bonding conductor in the ??1 inch pvc pipe from the control panel underground to the seal off vault?? and this bonding conductor was connected to the 4 RMC raceways and to the separately derived system at or near the control panel.

I could write an essay about this. This is one problem that occurs when two CMPs attempt to cover the same material in detail ? in this case, bonding in classified locations. Even when they mutually vet these areas there is a strong potential for unintended consequences.

First consider if the installation would have been compliant if classified locations were not an issue. If it were not compliant, then recognize simply adding supplementary EGCs would not make it compliant. This is true whether we are reviewing a Classified location or not.

Now add the classified locations issue. My personal opinion is that CMP 14 truly recognized what ?equipment bonding conductors,? as opposed to ?equipment grounding conductors,? were long before CMP 5 did. What they didn?t have was a proper name for them and they avoided stepping on CMP 5?s toes. So they described them rather than defined them.

CMP 14 determined a few bonding methods, that were otherwise acceptable in unclassified locations (the locknut-bushing and double-locknut types of contacts?), were not acceptable in classified locations. Then they described rather than defined that ?? bonding jumpers with proper fittings or other approved means of bonding shall be used [and] 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.?

If my assumption in the second paragraph is correct, the conductor is one such ?bonding jumper.? Bonding jumpers have no maximum length and are essentially sized the same as equipment grounding conductors under Section 250.102(D).

The ?problem? is with 250.100 since it is technically trying to apply ?Service? requirements as a general application is classified locations; however, properly understood, 250.92 (B)(4) suffices.

For the 12 years I was on the API Subcommittee on Electrical Equipment, I recommended they secure a position on CMP 5 to clarify this stuff.

In summary ? I agree with the AHJ.
 
petersonra said:
Inside the classified area he met the requirements. This paragraph clearly states you only have to meet the requirements of 250.92(B)(2)-(4) inside the classified area.
Click to expand...

Not sure about the end of that statement. Check out the commentary in the Handbook after 501.30(A) "....apply to raceways and raceway-to-enclosure connections both inside and outside the classified location."

I have interpreted that, for example that RMC conduit or MC-HL cable terminating at a device in a hazardous location and the other end in a panel board or MCC in the non-hazardous location requires both ends to meet 250.92(B)(2) thru (B)(4). This has not always made me friends among the electricians when they have to re-work the panelboard end.

That being said, I have transitioned from RMC to PVC, underground, after leaving a hazardous location, and never gave a second thought to raceway bonding at both ends.....:rolleyes: I hate it when I try to out-think myself...
 
What about 300.3(B) which requires all conductors foa circuit to be in the same raceway...it does allow a bonding jumper on the exterior per 250.102(E) where not longer than 6 ft
 
I apologize for not responding sooner. My office was moved over the week end and, in the move, they misplaced my “mouse.” While I could read threads with some difficulty, responding was a nightmare.

As I said, I could write an essay about the problems that are caused when two CMPs attempt to cover the same subject in detail. And Section 300.2(B) would be at the top of the list.

Much of the content of 300.2(B) has been around a long time – the problem is that, as it relates to grounding and bonding, it doesn’t belong there – it belongs in Article 250. Technically,”… equipment grounding conductors and bonding conductors …” are NOT conductors of the same circuit and they are really not describing wiring methods either.

Taken literally, the main rule of 300 (B)(2) would make it impossible to have a “common” equipment grounding conductor for multiple circuits. Indeed “…the same raceway, auxiliary gutter, cable tray, [or] cablebus assembly, …” could not actually be used as EGCs at all since they are not themselves usually “… contained within …” another common enclosed system. I pointed this out to CMP 3 some time ago and suggested they refer to what was then the equivalent text of what is 250.134(B) now. “…otherwise run with…” is an adequate description of what is necessary. Unfortunately CMP 3 does not feel constrained by Charlie B’s rules. The Panel Comment indicated they believed the content of the two Sections were essentially identical. If that were true, of course, then 300(B)(2) would rarely be referred to for grounding requirements; although I have found that references to it tend to be exceptionally selective.

Ultimately, of course, the purpose of the NEC is “practical safeguarding” and the installation as described in the OP meets that. So - I still agree with the AHJ.
 
Last edited:
Status
Not open for further replies.
Top