Sub panel in new exterior shop

[mcspeed]

I’m in the elect planning stage of my shop build project.

16 x 28 wood frame building
When finished walls will have sheet rock, ceiling will be open to rafters to expose clerestory windows.

3-3-3-5 copper cable coming from 200 amp panel in house

Plan is to run 100 amp breaker in house panel to 12 space sub panel fed from bottom in shop.

Have studied FAQ section wyliediesel posted….thank you!

3-240v circuits 1@ for HVAC (30), compressor (30) welder (50).

3-120 v 20a circuits for misc lighting, outlets, garage opener
1- 120v 20a spare circuit

My main questions are:
1) The sub panel will be located Left of man door in pic and there is insufficient space for wires to run above door in wall. Can I run wires up to rafters and across without conduit/chase?
Keeping in mind rafters will remain open and walls sheet rocked. I of course want it to be safe, code compliant and look neat and tidy.

2) Confirm wire entering panel requires conduit?

3) Any access requirements for cable entering sub panel?

Any other thoughts and ideas are welcome and thanks in advance!



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[wyliesdiesels]

I would use aluminum over copper to save a bit of money (u didnt specify the length)

#1 al if you really need 100a or #2 al MHF if you can get by with 90a (you probably could, your load is not very high)

 

[pattenp]

What is the cable type you are thinking of using and how will it be run/installed between house and shop? 3-3-3-5, I'm smelling SER which is not allowed underground even in conduit.

 

[Norcal]

With a little prior planning a conduit could have been stubbed up in the stud bay to feed the panel.

 

[mcspeed]

May not have made it clear, cable is already in. Just need to pull it up through floor.


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[theoldwizard1]

Conduit requirements depending on the type of cable you have.

 

[mcspeed]

3-3-3-5 is USE and indoor is romex of the appropriate size for the circuits.

My understanding is that I don’t need conduit for USE if protected by drywall but wanted to verify.

What is not clear is any requirements on the rest of the wires being exposed in rafters. Most of which will be #12.


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[pattenp]

Something is not making sense. Does the cable have a jacket? If it's just USE then it's not approved for entering the structure. Will you post a pic of the cable?

 

[pattenp]

NM wiring can run exposed along the rafters as long as it's not exposed to damage. I assume no attic flooring from which the NM can be stepped on.

 

[mcspeed]

Thanks pattenp….. Hammering rain here so not able to get a pic. Yes it has a jacket. Will go inside wall 4-5’ to panel.


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[wyliesdiesels]

Thanks pattenp….. Hammering rain here so not able to get a pic. Yes it has a jacket. Will go inside wall 4-5’ to panel.


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If it has a jacket then its more likely SER, which is NOT permitted underground.

 

[pattenp]

It's sounding more like the cable is SE, but it's odd that you say it is USE. Could you have the letters mixed up and it's SEU? Which isn't the correct cable to use either.

 

[mike93lx]

Thanks pattenp….. Hammering rain here so not able to get a pic. Yes it has a jacket. Will go inside wall 4-5’ to panel.


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4",4' or 400' doesn't matter. If it isn't rated for in-structure use, it can't be there. Same with underground. Hopefully you didn't pull the wrong wire.

 

[dcg9381]

IF you run romex in those walls, make sure you're installing plates over the pass-through. Real easy to hit a wire in drywall. As others have mentioned, you do not need internal conduit unless your wire type requires it.

I would do at least one 1" conduit run from your panel for "future use" with a pull-string.

Any AV or internet?

As Wylie mentioned, might do the main run in aluminum... Just in case you haven't seen the prices of copper. 90A is the "sweet spot" for aluminum wire pull (within rational distances).

A building this size won't need 30A for HVAC. A 2-ton ductless system will pull under 12A continuous (at least mine does). It's different if you're using electric heat though...

 

[John in OH]

You don't mention if the sub-panel has a main breaker or not.

IIRC, (and it's been a LONG time since I studied the code) I thought a main disconnect was required in sub-panels in separate buildings???

Maybe some others here on GJ can clarify my foggy memory.

 

[joe6344]

Get a bigger panel. It's not much more expensive now and you are already out of spaces.

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[dcg9381]

I think a disconnect is required also (not going into all the exceptions). Easy enough if you're feeding a breaker in that panel.

 

[wyliesdiesels]

You don't mention if the sub-panel has a main breaker or not.

IIRC, (and it's been a LONG time since I studied the code) I thought a main disconnect was required in sub-panels in separate buildings???

Maybe some others here on GJ can clarify my foggy memory.

only if there is more than 6 branch breaker handles

 

[John in OH]

only if there is more than 6 branch breaker handles

So, based on the "6 branch breaker handles" criteria, it appears that a main disconnect is required.

I also agree with a previous poster that bigger is better as far as panel size goes ... you never know what the future may bring.

 

[alfredeneuman]

I think a disconnect is required also (not going into all the exceptions). Easy enough if you're feeding a breaker in that panel.

Disconnects are required for all detached building panels as is a grounding electrode system.

 

[dcg9381]

Disconnects are required for all detached building panels as is a grounding electrode system.

I think we're saying the same thing. But for clarification, isn't a feed breaker (properly labeled and installed, ie - screwed in) a valid disconnect?

 

[alfredeneuman]

I think we're saying the same thing. But for clarification, isn't a feed breaker (properly labeled and installed, ie - screwed in) a valid disconnect?

A main breaker is a form of disconnect, whether it's backfed and screwed down or factory installed.

 

[Terry D]

We really need a picture of the cable you installed. Is it direct bury or is it in conduit underground from the house. What do you mean when you say you have to pull it up through the floor.

I would install a larger sub panel with a main breaker for the disconnect, you are already using 10 spaces out of your 12 space panel. And if you back feed a breaker for your main, you will use all 12

 

[wyliesdiesels]

I think we're saying the same thing. But for clarification, isn't a feed breaker (properly labeled and installed, ie - screwed in) a valid disconnect?

a feed breaker wouldnt count since its in a different building

 

[alfredeneuman]

My comment about breakers is limited to the new panel in the detached building. There must be another disconnect in the new building.
A breaker ahead of the feeder is insufficient.

 

[dcg9381]

A main breaker is a form of disconnect, whether it's backfed and screwed down or factory installed.

Doesn't it have to be labelled? One of my panels has a feed breaker which is screwed in.. I assume that's so you cant easily get it free and mistake it for something that isn't backfed (think it isn't live).

 

[dcg9381]

a feed breaker wouldnt count since its in a different building

I know you're a stickler on the verbiage. I'm meaning a breaker in the shop/garage that is backfed. What's the correct name for that?

 

[Terry D]

I know you're a stickler on the verbiage. I'm meaning a breaker in the shop/garage that is backfed. What's the correct name for that?

Main breaker - which would also serve as a disconnecting means for the shop

 

[dcg9381]

Main breaker - which would also serve as a disconnecting means for the shop

In many panels, the "main breaker" is obvious as it's centered and out of the way of the other breakers. In load centers (assuming this is the right word) that have a fed-breaker, I thought that breaker had to be labelled and mounted in a manner that makes it not easy to remove? Otherwise there is no other way to recognize this as a feeding breaker.

 

[Terry D]

In many panels, the "main breaker" is obvious as it's centered and out of the way of the other breakers. In load centers (assuming this is the right word) that have a fed-breaker, I thought that breaker had to be labelled and mounted in a manner that makes it not easy to remove? Otherwise there is no other way to recognize this as a feeding breaker.

Yes. When back feeding a breaker for the the main, it must have a hold down device and be labled as MAIN. The reason being that when working on the panel with the cover off, if that back fed breaker came off the buss, it would have energized parts. The 100 amp eaton BR panels used to come from the factory with a 2 pole 100 amp breaker back feed with a hold down screw. Dont know if they still do
I never cared for BR panels

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[Norcal]

Yes. When back feeding a breaker for the the main, it must have a hold down device and be labled as MAIN. The reason being that when working on the panel with the cover off, if that back fed breaker came off the buss, it would have energized parts. The 100 amp eaton BR panels used to come from the factory with a 2 pole 100 amp breaker back feed with a hold down screw. Dont know if they still do
I never cared for BR panels

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A plug in breaker requires a hold down but most here are not going to use panelboards with bolt on breakers. I agree about BR panels or as I call them “Zinsco II”.

 

[dcg9381]

When back feeding a breaker for the the main, it must have a hold down device and be labled as MAIN.

thanks!