Another subpanel question

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  #1  
Old 04-25-07, 11:06 PM
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Another subpanel question

Hi all,

I have done a search and read through countless subpanel threads, which made me want to hire an electrician to do this, but I'd really prefer to do it myself.

My house has a new 200-amp main panel, with the main electrical loads being a 240v spa and an electric oven. I have a small detached rear house/shop (~300sf) that I am remodeling, and would like to rewire it properly. Suffice it to say that it needs to be completely rewired. It currently has 3/4" non-metallic conduit running from the main panel to the small house, about a 50-foot run.

The space will be used as an office/guest bedroom/laundry. What I would like to do is install a subpanel, to supply power to a 240v wall ac/heating unit (20 amps), a 120v washing machine, a gas dryer (also 120v), and about 8 other receptacles (for anything from a computer to a plasma TV). I will have 2 ceiling fans (with lights) and a track light on one circuit, the washer and dryer each on a circuit, a separate 240v circuit for the ac, and 2 circuits for the various receptacles. 6 breakers in total.

From what I've seen, I should be looking at a 60A-100A subpanel, running 3 6-gauge wires and a 10-gauge ground, with an 8' grounding rod.

Is that correct? Are there any other considerations I need to be aware of?

Will those wires fit through the existing 3/4" conduit, or do I need to dig up my recently-landcaped yard to run new conduit?

Is this something that I should be able to tackle myself, or should I leave it to the pros? Considering the 200A panel upgrade set me back over $2000, I'd prefer to do it myself, but I want to do it right.
 
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Old 04-26-07, 03:46 AM
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A 60 amp panel would do, but a 100 amp would give you room for expansion.

The 3/4 is too small either way, so there goes the lawn, but if you are carefull in three weeks you will not be able to tell.

Three number 2 copper with a number 6 ground in a 1 1/4 pvc conduit would work for a 100 amp panel. Three number 6 copper with a number 10 ground for 60 amps.

You can leave the existing pvc for phone and CATV.

BTW that was a great price for the service.
 
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Old 04-26-07, 10:55 AM
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A 60A subpanel will work with your existing conduit: (3) #6 + (1) #10 does fit in a 3/4" PVC conduit -- it's a 35% fill and code allows up to 40%. I'm not saying it'll be an easy pull, but with a lot of cable lube and careful pulling you should be okay.

From the loads you described, I think a 60A panel should be plenty adequate for your needs.

> Is that correct? Are there any other considerations I need to be aware of?

You seem to have it straight. Just remember to keep the grounds and neutrals separate in the subpanel. If your subpanel has more than 6 breakers, you need a main breaker in the subpanel. Some inspectors will require a main if the panel _can_ have more than 6 breakers, even if you only have a few installed. I would recommend a main breaker in the sub anyway.
 
  #4  
Old 04-26-07, 02:41 PM
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Thanks for the input! I'm going down to pick up a 100A GE subpanel w/main breaker at Lowes right now. Glad to hear that the wires will fit in the 3/4" conduit - I'd rather have the frustration of pulling the wires than digging up the yard.
 
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Old 04-28-07, 10:38 PM
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Its a feeder, #4 would work for 100amp. #2 would be 125amp.
 
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Old 04-29-07, 08:52 AM
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kellyandjulie,

If you read up a few posts, you will see that if you are running a 100amp sub, the 3 #2 WG wire will not fit in the 3/4" conduit you already have.


You can get a 100amp sub and use a 60amp breaker with the 3 #6 and #10 ground and be okay.
 
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Old 04-29-07, 07:22 PM
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Thanks - yeah, I've got a 60A main breaker for the new panel, and will run 3x 6-gauge and 1x 10-gauge ground.

What's the best way to fish the wires through the conduit? One at a time, or all at once? If all at once, what's the most effective way to do it?
 
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Old 04-29-07, 07:53 PM
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Use the old wires to pull the new wires, or run a string through and then use it to pull the new wires. Use plenty of wire lubricant. Use only wire lubricant, do not use anything else.
 
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Old 05-01-07, 12:23 PM
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So is it generally easier to pull them one at a time or all at once?
 
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Old 05-01-07, 12:24 PM
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All at once.
 
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