I've got an old 50amp subpanel in my house that does not have a ground conductor. Both the main and sub are in my house (no out buildings). The feeders are run to the subpanel through a flexible metal conduit in my basement. I'm looking to have a new ground conductor run from the main to the sub. It would be easy to run a 10-AWG THHN wire along and through the overhead floor joists, but much more difficult to run conduit. Does NEC allow the use of a 10-AWG THHN wire to be run along and through floor joists used as the grounding electrode without conduit? If so, can someone refer me to the NEC section that allows this? Thanks!
THHN Wire Without Conduit as Ground between Main and Subpanel
- Thread starter Ebean
- Start date
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I am allowing this as it's a question about a code.
102 Inspector
Senior Member
- Location
- N/E Indiana
- Occupation
- Inspector- All facets
I will take a stab at this. Article 300.3(B) 2008 edition states that conductors of the same circuit shall be in a raceway or cable assembly so I would not accept an individual conductor to pulled separately. If the conductor is inside the existing flexible metal conduit, then okay. If the existing FMC qualifies and is used as a grounding conductor, then it needs to meet the requirements of 348.60.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
How old is the FMC? If it's very old it probably qualified as an EGC when it was installed. If it was then IMO nothing would prohibit you from running an exposed conductor between the two panels.
Crossing up terms. Do you need an equipment ground or a ground electrode conductor? For a subpanel, I would think you need an equipment ground. How old is this install? The flexible metal conduit may be your ground. FMC does, however, have limitations on acting as a ground depending on its size and the size of the overcurrent protecting the feeder (details are in 250.118(A)(5)).
The normal way to fix this is to pull the equipment ground through that conduit along with the other conductors. Is there sufficient fill volume for an additional #10 conductor? Running the eguipment ground separately on the outside can run you afoul of the rule regarding metallic wiring methods. With metal boxes and raceways, all conductors of a circuit need to follow the same path. If the ground enters through a hole separate from the knockout where the conduit goes through, you can get inductive heating on a fault.
The normal way to fix this is to pull the equipment ground through that conduit along with the other conductors. Is there sufficient fill volume for an additional #10 conductor? Running the eguipment ground separately on the outside can run you afoul of the rule regarding metallic wiring methods. With metal boxes and raceways, all conductors of a circuit need to follow the same path. If the ground enters through a hole separate from the knockout where the conduit goes through, you can get inductive heating on a fault.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
300.3(B) would generally require the bonding jumper to be run inside the FMC, but it has some exceptions. The relevant such allowance says:
250.130(C) is for branch circuits, so it would not apply to a feeder to a subpanel. 250.134(B) Exception No 2 does not apply as this is not a DC circuit. And 250.102(E) imposes a limit of 6' in length.
So unless the FMC run is 6' or less, the bonding jumper would need to be inside the FMC.
Cheers, Wayne
2017 NEC 300.3(B)(2) said:
250.130(C) is for branch circuits, so it would not apply to a feeder to a subpanel. 250.134(B) Exception No 2 does not apply as this is not a DC circuit. And 250.102(E) imposes a limit of 6' in length.
So unless the FMC run is 6' or less, the bonding jumper would need to be inside the FMC.
Cheers, Wayne
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
A bare EGC might work.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Even if it was not correct at the time, is there really anything prohibiting you from running an EGC, outside of the raceway between the two panels? It may not bring it up to code, but mostly the ahj can't make you bring things up to code anyway. Might depend on what the op is trying to accomplish exactly
Yes, thanks, I meant an equipment ground. The install is from around 1960. Based on the NEC section (thanks for that), I would need a separate equipment ground since the subpanel exceeds 20 amps (it is 50 amps). The FMC is long (65 feet), partially buried behind the ceiling and continuous. I think it would be exceedingly difficult to try to get a #10 conductor through FMC. Does that mean I am stuck running a new 4-wire feed between the main panel and sub then?
Conduit is supposed to be installed such that you can remove and replace the conductors. A 3/4" conduit should be able to take three #6's and a #10 and be within fill limits but it depends on the type of wire pulled there now. A 1" conduit would be easier but don't know what you have. The pull may not be easy because of the corrugated surface if it has more than 180 degrees of bends. You won't be able to just pull a #10 through it, you'll have to remove everything and repull 4 conductors.
This may have been legal at the time so technically no change would be required. I would ensure the conduit fittings have a good bond to each panel. Use a bonding bushing at each end to be sure unless it has good locknuts that are biting well into the chassis. I would be OK with a #10 clamped to the outside of the conduit at the origin and end and following the path of the conduit (using pipe ground clamps). The NEC may not have provisions for that, but it would be better that what you have since long FMC isn't a great ground path.
This may have been legal at the time so technically no change would be required. I would ensure the conduit fittings have a good bond to each panel. Use a bonding bushing at each end to be sure unless it has good locknuts that are biting well into the chassis. I would be OK with a #10 clamped to the outside of the conduit at the origin and end and following the path of the conduit (using pipe ground clamps). The NEC may not have provisions for that, but it would be better that what you have since long FMC isn't a great ground path.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Are you sure that it is FMC and not type AC cable? They look the same although FMC would probably have to be much larger- like 1-1/4" just to be able to pull the conductors through. Probably the last thing I would want to do is pull #6s through that length of flexible conduit anyway. I certainly have run 6/3 AC for ranges. If that's the case, I wouldn't worry about the EGC.
-Hal
Thanks, Hal. You may be correct that it is AC cable. I attached a picture of the installation.
Attachments
- Location
- New Jersey
- Occupation
- Journeyman Electrician
It's not armored cable and from 1960 the raceway was permitted as the EGC. If you makes you feel warm and fuzzy there is nothing prohibiting you from running a jumper from one panel to the other.
Thanks, suemarkp. I think this sounds like a good solution.
Thanks, Rob. Yes, I think that makes sense.