240-volt window a/c receptacle in detached building

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Ravenvalor

Ravenvalor

Senior Member
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Piedmont region of NC
Hello,

Thanks for all of the great advice that you have given me throughout the years that I have been subscribed to this forum. The code book is a maze that I cannot navigate without your guidance.

A customer wants me to wire a detached 20 x 12 wooden storage building at his home.
It will have 5 - receptacles used for light duty and 3 - small light fixtures. I proposed installing a 20-amp double pole building disconnect switch and feeding it from a 20-amp double pole panel in the house. He also wants for me install a 240-volt receptacle in the building for a window a/c. Is there a certain size a/c that I should recommend, possibly something that pulls 10-amps or less?

Thanks for the help.
 
Keeping it under 10 amps @230V you are probably maxxed out at about 1.5Ton (18,000BTU) with a window AC unit. That may be a little small for a building that size, but it will depend on climate, insulation, number of windows, etc, however I am not an HVAC guy.

Not sure if I read your post right, but I think you may need more than a single double pole disconnect over there to feed the circuits you mention. Might make sense to put in a small 6 space panel IMHO.

---Aaron
 
Great info abrace. I called the customer and gave him the options. He still wants to stay within the 20amp range for the feeder circuit size though. At least now he knows that he will be limiting himself.
Thanks.
 
Ravenvalor said:
Hello,

Thanks for all of the great advice that you have given me throughout the years that I have been subscribed to this forum. The code book is a maze that I cannot navigate without your guidance.

A customer wants me to wire a detached 20 x 12 wooden storage building at his home.
It will have 5 - receptacles used for light duty and 3 - small light fixtures. I proposed installing a 20-amp double pole building disconnect switch and feeding it from a 20-amp double pole panel in the house. He also wants for me install a 240-volt receptacle in the building for a window a/c. Is there a certain size a/c that I should recommend, possibly something that pulls 10-amps or less?

Thanks for the help.
Click to expand...

Reading your post you distinguish between a two pole switch at the accessory building and a two pole breaker at the dwelling.

So you want to run a 240 volt branch circuit for a 240 volt window air-conditioner and tap the 20 amp 240 volt (switch) branch circuit with a 20 amp 120 volt branch circuit at the storage building.
I am not sure how you are doing this without defining this as two branch circuits at the storage building, I would think u would then have a feeder to the storage building and not supplying it with a single 240 volt branch circuit.
My way of thinking you should supply a small panel at the building with a feeder large enough for the anticipated loads at the building. I would try to persuade the owner that you have two branch circuits at the storage building and I would not tap the 240 volt branch circuit to create a 120 volt circuit.
 
Ravenvalor said:
Great info abrace. I called the customer and gave him the options. He still wants to stay within the 20amp range for the feeder circuit size though. At least now he knows that he will be limiting himself.
Thanks.
Click to expand...
If you want to do him a favor for when he decides 20 amps is not enough, you will install a large enough raceway to pull larger supply through without having to excavate again when that time comes.
 
kwired said:
If you want to do him a favor for when he decides 20 amps is not enough, you will install a large enough raceway to pull larger supply through without having to excavate again when that time comes.
Click to expand...

We are running UF but I can at least quote 12/3 UF in comparison with 10/3 UF for him to choose.
 
david said:
Reading your post you distinguish between a two pole switch at the accessory building and a two pole breaker at the dwelling.

So you want to run a 240 volt branch circuit for a 240 volt window air-conditioner and tap the 20 amp 240 volt (switch) branch circuit with a 20 amp 120 volt branch circuit at the storage building.
I am not sure how you are doing this without defining this as two branch circuits at the storage building, I would think u would then have a feeder to the storage building and not supplying it with a single 240 volt branch circuit.
My way of thinking you should supply a small panel at the building with a feeder large enough for the anticipated loads at the building. I would try to persuade the owner that you have two branch circuits at the storage building and I would not tap the 240 volt branch circuit to create a 120 volt circuit.
Click to expand...

This is a routine procedure in central North Carolina. Most people use storage buildings for storage. Building disconnect is a double pole switch, come out of it with three 12/2 UF cables, 1 - for the lights, 1 - for one set of receptacles, 1 - for another set of receptacles. This customer just wants to run a 240-volt air conditioner also. He is a school teacher on a limited budget. Plus they have a house full of kids.
 
Ravenvalor said:
This is a routine procedure in central North Carolina. Most people use storage buildings for storage. Building disconnect is a double pole switch, come out of it with three 12/2 UF cables, 1 - for the lights, 1 - for one set of receptacles, 1 - for another set of receptacles. This customer just wants to run a 240-volt air conditioner also. He is a school teacher on a limited budget. Plus they have a house full of kids.
Click to expand...
Everyone is always on a budget. I'd bury inch PVC and still only pull 12AWG if he wants to be cheap. In a few years when he wishes he had run a 60 amp circuit you won't need to tear up the yard to replace the UF, or have to charge him the labor to excavate it again.

If building is for storage why does it need air conditioning, seems to me he plans to spend some time in there if he wants AC, that may mean hobbies, crafts, or even just DIY small projects that may utilize power tools and the need for a little more power at times.
 
Ravenvalor said:
This is a routine procedure in central North Carolina. Most people use storage buildings for storage. Building disconnect is a double pole switch, come out of it with three 12/2 UF cables, 1 - for the lights, 1 - for one set of receptacles, 1 - for another set of receptacles. This customer just wants to run a 240-volt air conditioner also. He is a school teacher on a limited budget. Plus they have a house full of kids.
Click to expand...

I can see the general purpose multiwire branch circuit for the lighting and receptacles.

Ravenvalor said:
This customer just wants to run a 240-volt air conditioner also.
Click to expand...

When you add 240 volt air conditioner to a multiwire branch circuit in my way of thinking you have a 240 volt branch circuit. I would not define a 240 volt branch circuit for the air conditioner as a 120 volt multiwire branch circuit.

It is my view that you should have a min. of two branch circuits.
I think 225.39 (B) 2008 version or what ever section that would be in the 2011 or 2014 codes

edit: I feel the circuit to the storage building needs to be a feeder
 
david said:
I can see the general purpose multiwire branch circuit for the lighting and receptacles.



When you add 240 volt air conditioner to a multiwire branch circuit in my way of thinking you have a 240 volt branch circuit. I would not define a 240 volt branch circuit for the air conditioner as a 120 volt multiwire branch circuit.

It is my view that you should have a min. of two branch circuits.
I think 225.39 (B) 2008 version or what ever section that would be in the 2011 or 2014 codes

edit: I feel the circuit to the storage building needs to be a feeder
Click to expand...

How about 210.4(C)?

(C) Line-to-Neutral Loads.


Multiwire branch circuits shall supply only line-to-neutral loads.


Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.


Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.
Click to expand...
Exception 2 is kind of redundant IMO as we have been required to open all conductors simultaneously for several years now on all MWBC. (since 2008 I think, but could have been 2005)

However I think there is a chance one must have a common trip breaker and not just handle ties for the 240 volt AC, need to dig deeper to find that though.
 
I can understand the limited amount of funds, but I think that is the bases of defining the supply needs to this storage building as a single 20 amp general purpose multi-wire branch circuit.

That would Avoid the cost of a small panel, branch circuit devises, grounding electrodes, min. feeder based on calculated load and consideration given to 225.39

My feeling is a larger feeder needs to supply the storage shed or the idea of a small 240 volt AC unit needs to be dropped.
 
david said:
I can understand the limited amount of funds, but I think that is the bases of defining the supply needs to this storage building as a single 20 amp general purpose multi-wire branch circuit.

That would Avoid the cost of a small panel, branch circuit devises, grounding electrodes, min. feeder based on calculated load and consideration given to 225.39

My feeling is a larger feeder needs to supply the storage shed or the idea of a small 240 volt AC unit needs to be dropped.
Click to expand...
Maybe get a 120 volt AC instead? then you can have one half of the MWBC mostly dedicated to the AC maybe include some fixed lighting, and the other to general use receptacles?

Again this is supposed to be done "cheap" is supposed to be "storage" yet needs an air conditioner:huh:
 
kwired said:
Maybe get a 120 volt AC instead? then you can have one half of the MWBC mostly dedicated to the AC maybe include some fixed lighting, and the other to general use receptacles?

Again this is supposed to be done "cheap" is supposed to be "storage" yet needs an air conditioner:huh:
Click to expand...

That works, i thought of a small 110 volt unit as well maybe that design will work for the OP and this homeowners needs.
 
kwired said:
How about 210.4(C)?

Exception 2 is kind of redundant IMO as we have been required to open all conductors simultaneously for several years now on all MWBC. (since 2008 I think, but could have been 2005)

However I think there is a chance one must have a common trip breaker and not just handle ties for the 240 volt AC, need to dig deeper to find that though.
Click to expand...

Hey kwired,

What is the difference between a common trip breaker and handle ties?

Thanks,
 
In other words, both thermal and magnetic trip in either pole will open both poles.
Because, in part, of the required "free trip" operation of each pole you cannot rely on the handle of the tripped pole to force the handle of the other pole into the off position.
The handle tie affects only manual operation, and notice that it generally takes requires you to open both poles in order to reset one tripled pole.
 
Follow Up

Follow Up

I gave the customer a quote with a 30-amp feeder and an electrical panel at the building.
He turned the quote down stating the price was not in his budget.

So I turned to the local inspector to see if he would let me run a 20-amp feeder and not install an electrical panel. The inspector denied the request because he viewed the feeder as an A/C circuit and said that it had to be dedicated. Even though it was plug and cord.
 
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