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6% voltage drop for 60 amp sub panel?

12K views 63 replies 11 participants last post by  andrew79 
#1 ·
Hello,

I am planning on installing a 60 amp sub panel in my detached garage. Originally I was going to run (3) #6 THWN feeders with a #8 ground, buried in conduit. The total distance from main panel to sub panel is about 160 feet.

After using a voltage drop calculator at southwire, it is saying my voltage drop is going to be 6%+ using this wire.

1) At what percent of voltage drop should I try to stay under?

2) Southwire calc is recommending #2 THWN or #2/0 Aluminum for my feeder, does this sound about right?

Thanks for the help!
 
#3 ·
Thanks Speedy... Right now, I'm only planning on using overhead lights and a space heater. This will be used for storage of products for my home based business. When I finally decide to use it as regular garage, I will have more load from the typical tools such as a table saw, compressor, etc... I'm not real sure what calculated load I should be going for. Any thoughts?
 
#7 ·
Speedy's most likely right with the number 4 I would think. Still smaller than 2 so should save you some coin.

It depends on your heater. You can really only have one or two tools running at the same time so the wattage of your heater will determine your service size for the most part.
 
#16 ·
I'm confused, I thought you said you were running individual conductors in PVC/conduit?

Could you post the link to what you found?
 
#19 ·
OK, I see the confusion, they were talking about #2, but you posted 2/0. You still aren't going to want to pull SER thru PVC.
 
#23 ·
Yes it is. PVC glue is very corrosive when wet. Plus it helps ensure you don't have to many bends in the conduit.
 
#25 ·
Oh, there you go. I didn't know this because I've never wanted to do it, but you cannot use type SE cable underground.

338.12 Uses Not Permitted.
(A) Service-Entrance Cable. Service-entrance cable (SE)
shall not be used under the following conditions or in the
following locations:
(1) Where subject to physical damage unless protected in
accordance with 230.50(A)
(2) Underground with or without a raceway
(3) For exterior branch circuits and feeder wiring unless
the installation complies with the provisions of Part I of
Article 225 and is supported in accordance with 334.30
or is used as messenger-supported wiring as permitted
in Part II of Article 396
 
#27 ·
No, you could use #2 XHHW. Its an aluminum single conductor, but I would use #4 CU if the 60A breaker was rated to accept it.
 
#32 ·
If I was to just do a new 100 amp service on this detached garage instead of running a sub panel to it, is installing a new service for garages pretty much the same (code wise) as residential installs?

To do a sub panel it will cost me $900 in materials + $170 to rent the trencher.

To do a new service, it will only cost me about $350 including insp fees.
 
#34 ·
Yeah, it is $5.00 per month. Even at 12 years later, the monthly meter fee + the new service cost would finally equal the same cost as running a sub panel. Plus I wouldn't have to tear up the yard and I would have 100 amps at garage, instead of 60 :)

I'm just not sure if there any additional code requirements for doing a new service in a garage vs a house.
 
#36 ·
A drop of 6% is not going to worry most overhead lights,
Neither is it going to effect a space heater to any large degree.
However things like table saws and compressors are likely to
be effected more than the lights.
Most motors require a large start up surge,
This is where you might have problems.
For long term compatability use the largest wire
you can afford, this will minimise any problems.
 
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