Minimum AWG wire that can feed a sub panel

[yeild]

Is there a NEC requirement for what size wiring has to be ran to a sub panel? If the homeowner wants to run power to a detached garage and only really wants a small sub panel with with a few breakers for lights and outlets, does it have to have a minimum AWG wire feeding a sub panel? Does it have to have both red and black hots if he doesn’t want/need 208/240 for anything in the garage? I was told by an electrician that a minimum 4AWG needed to be ran to the sub panel and that a black and red had to be ran. The homeowner had already ran a 10/2 Romex through underground conduit from his main to the sub panel and now had asked me whether he has done it to code. Also, I have informed him about the grounding for the sub panel but was unclear about if there is a NEC code about how far the grounding electrode can be from the sub panel. Is only one grounding electrode needing to connect to the sub panel because I was told I needed 2 spaced 8 feet apart. To avoid cutting/drilling into his concrete slab, can the electrode be driven in outside the building and then ran through the side into the sub panel? The ground wire from the electrode would be about a 15 feet run.

 

[augie47]

On the positive side, there is no minimum size for the conductor and you can run 120 only or 120/240. You can run a 20 amp MWBC and not have a panel or a larger feeder to a panel.
Other than green for your equipment ground and white for your neutral, color does not matter in this instance.(If you elect to run UF obviously the EGC would be bare)
The panel will require a grounding system,m normally 2 rods spaced 6 ft apart.
On the negative side, NM (Romex) can not be installed in an underground conduit,

 

[infinity]

The feeder or branch circuit size would be determined by the load.
The 10/2 NM cable is no good and needs to be ripped out.
There is no #4 AWG minimum feeder size so the electrician is incorrect.
As mentioned a sub panel requires a GES typically two ground rods.
A single MWBC would still require a disconnecting means at the separate structure.

 

[LarryFine]

Welcome to the forum.

The minimum wire size is that which is needed to supply the maximum expected load.

As Augie touched on:

Romex is wrong anywhere outdoors at all, ever, in a conduit or not.

A sub-panel in a detached structure needs its own electrode system.

There should always be separate neutral and grounding conductors.

Yes, your electrodes can be driven outside and the GEC routed inside.

One vs two line conductors (120v vs 120/240v) is a design choice.

The labor is the same either way. Use the Romex to pull in new wires.

 

[yeild]

On the positive side, there is no minimum size for the conductor and you can run 120 only or 120/240. You can run a 20 amp MWBC and not have a panel or a larger feeder to a panel.
Other than green for your equipment ground and white for your neutral, color does not matter in this instance.(If you elect to run UF obviously the EGC would be bare)
The panel will require a grounding system,m normally 2 rods spaced 6 ft apart.
On the negative side, NM (Romex) can not be installed in an underground conduit,

Thanks. I was unsure about the whether the sub panel had to be wired with 240 even it wasn’t needed. I told the homeowner if it was me, I would wire it now to be able to put a 240 breaker in if he ever wanted to have a welder, plasma cutter or a large air compressor in the future. 6’ is good to know. But there isn’t a maximum length for the ground wire going from the grounding rod to the sub panel? I don’t want to tell him the grounding is good and then find out later that the building isn’t protected properly because the ground wire run going to the grounding rods is too long.

Also, does a sub panel require a disconnect, either a main breaker disconnect or a disconnect outside the sub panel in the near vicinity, or does the breaker from the main feeding the sub satisfy the disconnect requirement, if necessary, even if the main panel is in the house?

 

[yeild]

Welcome to the forum.

The minimum wire size is that which is needed to supply the maximum expected load.

As Augie touched on:

Romex is wrong anywhere outdoors at all, ever, in a conduit or not.

A sub-panel in a detached structure needs its own electrode system.

There should always be separate neutral and grounding conductors.

Yes, your electrodes can be driven outside and the GEC routed inside.

One vs two line conductors (120v vs 120/240v) is a design choice.

The labor is the same either way. Use the Romex to pull in new wires.

Thank you. I didn’t think Romex was appropriate but they had already done a lot of the work themselves before contacting me on whether it was up to code. I had told him I would prefer he ran individual THWN conductors to the sub panel but would check to verify code requirements. I honestly think him running the Romex was probably a pain to pull instead of individual conducts pulled through together. But again, I was only consulted after the fact. Now I’m trying to get him where he needs to be. I did make sure that the neutral was not bonded to the sub panel and made sure he had installed a separate ground bus that is not bonded to the neutral.

 

[infinity]

I'm glad that they came to you for help albeit a little too late but this is a good example of why DIY work performed by a homeowner should not be done when they are not qualified.

 

[ramsy]

But again, I was only consulted after the fact. Now I’m trying to get him where he needs to be.

Owner builder permits are available to homeowners, who are typically required to sign indemnity clauses, so the inspectors can do their job without getting sued.

Those inspectors would be more familiar with any amendments that change the NEC adoptions, and allow for more than one correction or visit.

The advantage of getting permits is being able to count the project as certified work experience toward your contractors license.

Help a few more friends, get your license, and you'll be telling us what to do.

 

[ramsy]

told by an electrician that a minimum 4AWG needed to be ran to the sub panel and that a black and red had to be ran.

230.79(C) only applies if meter is installed.

225.39(C) only applies with occupancy.

If anyone lives in garage, #1cu AWG is required, since PVC and most non-metallic conduit is not listed for temperatures > 60°C.

To pay the mortgage in metro areas like mine, owners have to rent out the garages.

The city of Santa Ana, and others, have allowed multiple occupants per room, where immigrants use bed sheets to partition the living space for multiple families.

 

[yeild]

The advantage of getting permits is being able to count the project as certified work experience toward your contractors license.

Help a few more friends, get your license, and you'll be telling us what to do.

I’ve done electrical work all my life and am looking into getting licensed to go with my locksmith license as well. Thanks for the information.

 

[infinity]

If anyone lives in garage, #1cu AWG is required, since PVC and most non-metallic conduit is not listed for temperatures > 60°C

Are you saying that rigid PVC conduit is limited to 60° C? It says right on it 90° C conductors.

 

[yeild]

230.79(C) only applies if meter is installed.

225.39(C) only applies with occupancy.

If anyone lives in garage, #1cu AWG is required, since PVC and most non-metallic conduit is not listed for temperatures > 60°C.

To pay the mortgage in metro areas like mine, owners have to rent out the garages.

The city of Santa Ana, and others, have allowed multiple occupants per room, where immigrants use bed sheets to partition the living space for multiple families.

The garage is only for him to do work in. Just little small things but still have tried to talk him into wiring it to be able to handle whatever in the future. That way he wouldn’t have to worry about redoing things later. Plus it would be a better selling point if the garage was already wired with 240 if he ever decided to sell the house in the future but I doubt he would.

 

[rc/retired]

I’ve done electrical work all my life and am looking into getting licensed to go with my locksmith license as well.

I'm calling you if I get locked out of my electrical room!
Good luck

Ron

 

[yeild]

I'm calling you if I get locked out of my electrical room!
Good luck

Ron

I can definitely get in.

 

[ramsy]

Are you saying that rigid PVC conduit is limited to 60° C? It says right on it 90° C conductors.

Except for some elbows & nipples, schedule 80 rigid PVC in my area is not sold in big box stores, which most owner builders exclusively rely on for their building materials, besides the unlisted devices, fixtures, and appliance hazards from China, purchased on Amazon.

 

[LarryFine]

But there isn’t a maximum length for the ground wire going from the grounding rod to the sub panel? I don’t want to tell him the grounding is good and then find out later that the building isn’t protected properly because the ground wire run going to the grounding rods is too long.

No limit. Short and straight are goals, but not requirements.

Also, does a sub panel require a disconnect, either a main breaker disconnect or a disconnect outside the sub panel in the near vicinity, or does the breaker from the main feeding the sub satisfy the disconnect requirement, if necessary, even if the main panel is in the house?

Yes, the detached structure requires a disconnect, whether a switch, a main breaker, or a max of six breakers.

 

[norcal]

Minimum size conductors would be based on the lugs, based on the lower end of the range of the conductors the lugs are rated to accept.

 

[infinity]

Except for some elbows & nipples, schedule 80 rigid PVC in my area is not sold in big box stores, which most owner builders exclusively rely on for their building materials.

Not sure what you mean but here's an old scrap piece of SCH40 I had laying around.

 

[yeild]

No limit. Short and straight are goals, but not requirements.


Yes, the detached structure requires a disconnect, whether a switch, a main breaker, or a max of six breakers.

Thank you. The ground will be as short and straight as possible.

The sub has a main breaker on it.

 

[ramsy]

Not sure what you mean but here's an old scrap piece of SCH40 I had laying around.

View attachment 2572216

Thats not a continuous rating.

Plastic Pipes - Maximum Operating Temperatures

Piping materials like ABS, PE, PVC, CPVC, PB, PP and SR and pressure and operating temperature limits.

www.engineeringtoolbox.com

But perhaps ok for residential feeders not considered continuous loads.