Reality check cable size

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endly

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Hello

I could use a final reality check reagrding conductor size to a sub-panel. I'm getting varying opinions.

I'm installing a 125 amp sub-panel to a detached garage with the sub-panel located in the garage. I am going to power the sub-panel from a 125 amp breaker in a existing, new, service. The distance is about 40' feet.

My question is what size cable to run? I have found three different answers. I will be using THHN/THWN in 1-1/2 conduit. At present I have opinions of #2, #3, and #4.

Thanks for your feedback.

Richard
 
Re: Reality check cable size

What is the temperature rating of the terminals the conductors are connecting to?

How many current carrying conductors are in the raceway?

What is the calculated load?
 
Re: Reality check cable size

Calculated load is very small but I don't know the numbers offhand...

2-15 amp general lighting
2-20 amp small appliance
1-20 amp bathroom
1-15 amp refer

Might add another 50 amp circuit.

Square footage of building maybe 400 square feet.

Not sure the termination temps. Typical 125 amp Home Depot Panel.

New raceway nothing else in it except service to this panel. Perhaps I could do with 1-1/4" inch conduit?

[ May 24, 2005, 07:14 PM: Message edited by: endly ]
 
Re: Reality check cable size

I think the point people were trying to make that you seem to have missed is that there are a lot of things to consider when deciding these things. They only brought up a couple of them.

Heres a few more:

What kind and how many grounding electrodes do you intend to use at the garage?

Will you be connecting the ground and neutral together at the new subpanel?

It is far safer and better in the long run to pay someone who already knows the answers to these questions rather than risk killing someone because you do not know the answers yourself. You may not even know all the questions.

[ May 24, 2005, 08:11 PM: Message edited by: petersonra ]
 
Re: Reality check cable size

125A feeder to a detached garage seems like overkill, but if you are intent on using a 125A bkr. as the feeder OCPD:

Assume 120/240V. 1-phase 3-wire typical residential electrical system, terminations are probably rated 75 degree C, use THHN/THWN wire - then (3) #2 with (1) #6 equipment ground (bond) in 1-1/4" raceway should be fine.

Get licensed electrician to do the work.
 
Re: Reality check cable size

somehow,I don't think he needs one...now


Edited:-not today anyway..

[ May 24, 2005, 08:18 PM: Message edited by: dillon3c ]
 
Re: Reality check cable size

somehow,I don't think he needs one...now
Click to expand...
:)

Thank you very much. Licensed electrician or not it's about a safe and sane installation, is it not?

And just for the record, I have done MUCH electrical study and commercial and residential apprenticeship but I've been out of the trade for six years. This particular area of sizing I have low self-confidence in trusting myself with. It's a bitty job, but still, it's about a safe and sane installation. I take pride in my work therefore I asked YOU!

:cool:

Thanks again!

Richard

[ May 24, 2005, 09:11 PM: Message edited by: endly ]
 
Re: Reality check cable size

You may.. "start hearts with a chest massage on your spare time",and subscribe the American Journal of Medicine..(it doesn't make you a MD )

Your profile says handyman sir....Period.... And for the record the apprentices are advised in the same..The electricians of this site,don't instruct apprentices,in performing work alone..

Hire a licensed Electrical Contractor to perform the work..

[ May 24, 2005, 09:38 PM: Message edited by: dillon3c ]
 
Re: Reality check cable size

P.S. In reply to petersonra...

I will be using two grounding electrodes, eight feet long driven entirely and placed at least eight feet apart.

Ground and neutral WILL NOT be connected at the new subpanel! Neutral is floating.

I really am grateful for your input. I stand both humbled and enlightened.

Richard
 
Re: Reality check cable size

Originally posted by endly:
Ground and neutral WILL NOT be connected at the new subpanel! Neutral is floating.
Click to expand...
So you are running a grounding conductor to the garage then, right? This is crucially important, either way you go you need to do that method the right way.
 
Re: Reality check cable size

This NEC? Forum is for those in the electrical and related industries. Questions of a "How-To" nature by persons not involved in the electrical industry will be removed without notice.

I would prefer to send you a private message but you have turned that feature off. I am locking this thread.
 
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