Multiple parallel ground wires in a conduit

Status
Not open for further replies.
C

Carultch

Senior Member
Location
Massachusetts
I've got a job where what got built doesn't match what was on the drawing set. Instead of the correct single wire, double ground wires each individually of an insufficient size were installed. The wires are in the same conduit. The two ground wires do both "add up to" what you would need, both in terms of adding the amp values in Table 250.122, and in terms of adding up the KCMIL.

Anyone know of any code reference that would allow this? I'd rather not have the debate if I don't have to.

My understanding is that it is not correct. My understanding is that no matter what the situation of paralleling, if an EGC wire is installed, all conduits need a full size equipment ground wire that can carry the fault current on its own.

Example: a 200A circuit, with a #6 Cu ground specified, but with two #6 Al grounds installed instead.

#6 AL is rated to be the ground wire of up to 100 A, and intuitively one might think that 2 parallel #6 AL grounds could be rated for 200A. And the KCMIL add up as well, since 2 x #6 is the same kcmil as a #3.
 
Equipment grounding conductors in same conduit

Equipment grounding conductors in same conduit

Read 310.4(B)(C)(D)(E) and remember (not smaller than 1/0) and you may have found what your looking for, let me know if you agree.......:D

now that's if, and only if it is a paralleled conductor situation. If its a basic conduit with branch circuits etc then it must be sized in accord with the largest circuit breaker as you said, I was thinking you were paralleling - option left is if the conduit is an approved mechanical grounding conductor like EMT or rigid pipe use that as your EGC and bond around the fittings and concentrics as required - some other conduit materials may be approved with what you actually have in the conduit now. when bonding around concentrics etc just be sure the conductors from there are at least the size of what you need.
 
Last edited:
another option

another option

carlutch - if none of those help ya just talk to your inspector and ask if you can put a GF or fault monitor on it. there may be other exceptions these guys can find in here - im in an 08 ! I know "my bad" its no secret the AHJ is final word and sometimes if it's safe and he deems it safe, both your heads may come up with something ok to both parties. I was in the biz and it happens all the time, if he's a decent guy he's not gonna wanna see ya tear it apart over a small technical issue - what about reducing the OCPD in your #6 scenario you gave? good luck and let me know how you make out, I'd work with ya and that's why I never had a problem with any of my electricians. - I got out - too darn political for me - no thanks. maybe when im super old and don't give a crapper any more i'll go back.......
 
There is no prohibition to having EGC's in parallel even if they're smaller than #1/0. You just can't use two or more smaller conductors to make one larger conductor to achieve the proper size required from T250.122.
 
ActionDave said:
Don't know any that allow it. Ones that prohibit it....250.122 (A), (B), (C), (F), (G).

The fact that the the NEC is a permissive code means that it is allowed if it is not prohibited, but when it is prohibited then it's prohibited.
Click to expand...

It turns out I convinced the guys to fix it. I hope they are glad I caught it before the inspector. I sure am.
 
infinity said:
There is no prohibition to having EGC's in parallel even if they're smaller than #1/0. You just can't use two or more smaller conductors to make one larger conductor to achieve the proper size required from T250.122.
Click to expand...

well said (i meant his phase conductors anyway regarding 1/0....:slaphead: you know the hot lmao!) lets be politically correct tho and say grounded and ungrounded conductors.
 
jbelectric777 said:
well said (i meant his phase conductors anyway regarding 1/0....:slaphead: you know the hot lmao!) lets be politically correct tho and say grounded and ungrounded conductors.
Click to expand...
He was politically correct - and you missed the correct term which he used - we are talking about an equipment grounding conductor here which is not the same thing as a grounded conductor. The "grounded" conductor also would need to be 1/0 minimum for paralleled conductors.

310.10(H)(1):

Aluminum, copper-clad aluminum, or copper conductors, for each phase, polarity, neutral, or grounded circuit shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger where installed in accordance with 310.10(H)(2) through (H)(6)
Click to expand...


back to the original topic, nothing prohibits multiple equipment grounding conductors in a raceway, but all of them need bonded together at junction boxes, outlet boxes, panels, etc, effectively making them parallel to one another. So if you had a 15 amp circuit and a 30 amp circuit in same raceway nothing would prohibit installing a 14 and a 10 AWG EGC but if only one EGC installed it would have to be at least 10 AWG in that instance, or if more then one installed at least one would have to be 10 AWG. To install more then one is kind of pointless, but not specifically prohibited either.
 
kwired said:
So if you had a 15 amp circuit and a 30 amp circuit in same raceway nothing would prohibit installing a 14 and a 10 AWG EGC but if only one EGC installed it would have to be at least 10 AWG in that instance, or if more then one installed at least one would have to be 10 AWG. To install more then one is kind of pointless, but not specifically prohibited either.
Click to expand...

Interesting scenario to notice. I think by instinct, I would have a problem with that. Not necessarily a code issue, but given two ground wires with the same origin and destination, you don't want the fault current from the 30A circuit to bottleneck thru that #14 wire by mistake. I'd think intuitively that given ground wires bonded at both ends, each ground wire would need to be sized for the worst case scenario circuit within the raceway.

If the EGC's originate or terminate at separate devices, then I'd have no problem with dissimilar EGCs for dissimilar circuits sharing a raceway.
 
Carultch said:
Interesting scenario to notice. I think by instinct, I would have a problem with that. Not necessarily a code issue, but given two ground wires with the same origin and destination, you don't want the fault current from the 30A circuit to bottleneck thru that #14 wire by mistake. I'd think intuitively that given ground wires bonded at both ends, each ground wire would need to be sized for the worst case scenario circuit within the raceway.

If the EGC's originate or terminate at separate devices, then I'd have no problem with dissimilar EGCs for dissimilar circuits sharing a raceway.
Click to expand...

I think you are putting way to much thought into this.

Given a steel frame structure most EGCs will be in parallel, from 15 amp branch circuits to 2000 amp feeders. Nothing will 'bottle neck', the current will split in the most efficient directions with the total impedance being reduced.
 
Carultch said:
Interesting scenario to notice. I think by instinct, I would have a problem with that. Not necessarily a code issue, but given two ground wires with the same origin and destination, you don't want the fault current from the 30A circuit to bottleneck thru that #14 wire by mistake. I'd think intuitively that given ground wires bonded at both ends, each ground wire would need to be sized for the worst case scenario circuit within the raceway.

If the EGC's originate or terminate at separate devices, then I'd have no problem with dissimilar EGCs for dissimilar circuits sharing a raceway.
Click to expand...
I know it doesn't seem right, but outside of the allowed "islolated ground" situation, we are required to bond all equipment grounding conductors together as well to the enclosure if the enclosure contains splices, taps or devices, so if you would happen to have more then one EGC in a raceway for some reason you really have no choice. About the only time I ever run multiple EGC's in one raceway is if you maybe have a tee conduit body and are going to split into two different directions but are not going to splice the EGC in the tee, or similar situation.
 
IMHO, there is no code problem with two EGCs in a conduit run as long as they serve different circuits OR each wire is individually sized as a full EGC.
What I have a problem with is when it takes the combined ampacity of the two wires to meet the required EGC size.
As noted many times before the mere existence of a raceway does not allow you to run an undersized wire RGC.
 
Status
Not open for further replies.
Top