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Electrician Question Re: Adding Sub Panel
Posted on 1/25/24 at 7:44 am
Posted on 1/25/24 at 7:44 am
I nearly completed re-wiring my house (DIY). The final section, on the far side from the main panel, I'd like to add a small sub panel. This will feed a few light circuits (mostly LED), and a 30 AMP to the garage. The garage circuit already exists in the main panel, will just move it to the sub which is 50 feet closer (no sub in garage). I already have #6 (3wire) cable and 60amp breaker in place from a prior electric range. The sub will be fed from that 60A breaker.
**Primary question: The existing #6 cable, with 2 hots and 1 neutral. I understand I'll need to separate the neutral and ground at the sub. To avoid running a separate ground from the main to the sub, can I sink a grounding rod close to the sub and ground to that? Or does the ground need to be from the main?
Thanks in advance!
(Later I will rewire the garage with its own sub, but still need to figure out how to pull new cable through the existing conduit under the driveway.)
**Primary question: The existing #6 cable, with 2 hots and 1 neutral. I understand I'll need to separate the neutral and ground at the sub. To avoid running a separate ground from the main to the sub, can I sink a grounding rod close to the sub and ground to that? Or does the ground need to be from the main?
Thanks in advance!
(Later I will rewire the garage with its own sub, but still need to figure out how to pull new cable through the existing conduit under the driveway.)
This post was edited on 1/25/24 at 7:47 am
3
Posted on 1/25/24 at 8:59 am to eatpie
quote:
To avoid running a separate ground from the main to the sub, can I sink a grounding rod close to the sub and ground to that?
Based on what I see, NEC calls for the sub-panel ground to be wired back to the main panel, and the ground and neutral bars need to be isolated from each other. NEC 250.32(B)(1) I believe is where you find this. I would pull a green grounding wire, #10 wire should be sufficient for the ground wire.
Perhaps one of the resident electricians can verify what I am telling you. I would also suggest you check the jacket on the 3-wire #6 to make sure it is not NM or UF wire. Since it was for a 60 amp circuit before, I expect it is not but I would always double-check.
For #6 wire
NM or UF are rated for 55 amps
THW, THWN, SE, USE, and XHHW are rated for 65 amps
THWN-2, THHN, XHHW-2, and USE-2 are rated for 75 amps
There can also be deratings for length.
But as I said, I suspect this is all good based on your statements that this circuit was used before and the run will be no longer than previously (if I read that right)
Posted on 1/25/24 at 10:25 am to mdomingue
Thank you. Yes, you read correctly. I'll check and confirm the #6.
I basically understood the NEC on the ground, but hoping it allows for simply adding a separate ground rod. Not a huge deal but easier in my scenario. I presume the NEC is basically saying the neutral and ground need to be separate at the sub (not bonded). Gut (albeit uneducated) understanding is that ground is ground, regardless of termination.
Waiting for resident electrician to opine...
I basically understood the NEC on the ground, but hoping it allows for simply adding a separate ground rod. Not a huge deal but easier in my scenario. I presume the NEC is basically saying the neutral and ground need to be separate at the sub (not bonded). Gut (albeit uneducated) understanding is that ground is ground, regardless of termination.
Waiting for resident electrician to opine...
Posted on 1/25/24 at 10:36 am to eatpie
I'm almost positive that NEC will require a dedicated ground wire from the main panel. Realistically though, it will be completely functional and safe if you sink a ground rod at the sub panel.
Jump over to Mike Holt forum for legit code nerds responses.
Jump over to Mike Holt forum for legit code nerds responses.
Posted on 1/25/24 at 10:51 am to Specktricity
quote:
Jump over to Mike Holt forum for legit code nerds responses.
Holt will tell you to run the ground to the main. It is related to safety devices like GFCI and arc-fault breakers
This post was edited on 1/25/24 at 10:52 am
Posted on 1/25/24 at 11:53 am to kengel2
quote:
The way I read it, is if your disconnecting means is in another building you will need both.
I'm thinking based on the OP that it is an attached garage so not a seperate building.
Posted on 1/25/24 at 12:28 pm to mdomingue
I just ran a 6/3 60a feed from main panel at house to detached garage, new load center in garage. I did not sink a ground rod at the garage, just bonded to the panel and checked and made sure I was grounded to the rod back at the main panel
It works fine
It works fine
Posted on 1/25/24 at 1:18 pm to eatpie
quote:
**Primary question: The existing #6 cable, with 2 hots and 1 neutral. I understand I'll need to separate the neutral and ground at the sub. To avoid running a separate ground from the main to the sub, can I sink a grounding rod close to the sub and ground to that? Or does the ground need to be from the main?
No..... You can only have one neutral/ground bond in your system. The neutral ground bond is at your main panel. From that point, all neutral and ground paths must remain separate and dedicated. You will need to run 2 hots, 1 neutral and a dedicated, properly sized EGC to your sub panel.
Posted on 1/25/24 at 1:21 pm to Specktricity
quote:
it will be completely functional and safe if you sink a ground rod at the sub panel
Multiple paths to ground can create issues. Not allowed, not recommended. You can only create these separate grounding electrode system bonding points at separately derived services (typically a transformer location).
EDIT: assuming all in same building. Separate building you can add the ground rod at the sub panel but you still have to have the ground conductor running from sub panel to main panel unless you put a main breaker in the sub panel.
This post was edited on 1/25/24 at 2:55 pm
Posted on 1/25/24 at 2:24 pm to cgrand
quote:
I just ran a 6/3 60a feed from main panel at house to detached garage, new load center in garage. I did not sink a ground rod at the garage, just bonded to the panel and checked and made sure I was grounded to the rod back at the main panel
It works fine
Of course it does, it just may not be code.
Posted on 1/25/24 at 2:25 pm to mdomingue
quote:
I'm thinking based on the OP that it is an attached garage so not a seperate building.
Ya, I don't know, he said conduit under the driveway. Just assumed it was detached. That article I linked has examples of it all though. It all references the 2023 NEC though, Kentucky looks like they are only on 2017. He'd be ahead of the game.
Posted on 1/25/24 at 2:32 pm to notsince98
OK, thank you. Just so I am clear, the bonded neutral/ground at the main panel will feed the neutral and separate unbonded ground bus at the sub (with separate ground wire)?
Unsure if I've provided enough information, but based upon what I have, what would be a minimum/properly sized EGC? 8?
*60A breaker (prior electric range breaker) to feed sub, #6 cable. New sub will have a couple 15A breakers (maybe a 20) and 1 30A to feed detached garage (already exists without sub, just moving the garage breaker for closer access and later adding sub to garage.)
Unsure if I've provided enough information, but based upon what I have, what would be a minimum/properly sized EGC? 8?
*60A breaker (prior electric range breaker) to feed sub, #6 cable. New sub will have a couple 15A breakers (maybe a 20) and 1 30A to feed detached garage (already exists without sub, just moving the garage breaker for closer access and later adding sub to garage.)
Posted on 1/25/24 at 2:53 pm to eatpie
quote:
OK, thank you. Just so I am clear, the bonded neutral/ground at the main panel will feed the neutral and separate unbonded ground bus at the sub (with separate ground wire)?
One neutral conductor from the main panel goes to the sub panel and lands on the neutral bus. The neutral bus in the sub panel will need to insulated/isolated from the enclosure so that it is not connected to the ground bus in the sub panel enclosure.
One EGC conductor will run from the ground bus in your main panel to the ground bus in your sub panel. The ground bus will likely be connected/bonded to your sub panel enclosure. This is normal. The ground bus doesn't require isolation. If it is isolated, you'll need to add a jumper from the ground bus to the enclosure somehow.
quote:
Unsure if I've provided enough information, but based upon what I have, what would be a minimum/properly sized EGC? 8?
If the EGC is copper and the upstream feeder breaker for that circuit is 60A, the EGC can be #10 AWG or larger. If the conductor is aluminum then it must be #8 or larger.
quote:
*60A breaker (prior electric range breaker) to feed sub, #6 cable. New sub will have a couple 15A breakers (maybe a 20) and 1 30A to feed detached garage (already exists without sub, just moving the garage breaker for closer access and later adding sub to garage.)
#6 AWG for the hot wires and neutral fed from a 60A breaker is correct if the wire is copper. If it is aluminum, it needs to be #4 AWG or larger.
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