feeder wire and sub panel size

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  #1  
Old 05-23-06, 06:34 PM
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feeder wire and sub panel size

I have searched and just want to clarify this.
70 feet run for subpanel for detached garage. I want 240 in there because I may get a basic welder, the garage is 500 sq feet and I am planning 6 outlets, and about 6 overhead flourescent lights, 1 garage opener. I will use normal power tools 1 at a time including a 120 volt compressor.
Will a 60 amp sub panel work?
If so, is 3 8awg (2 hot 1 neutral) and 10 awg ground good enough buried in 1 in. 40 pvc 24 inches deep.
Or is 3 6awg and 1 8 awg required for this set up.
The garage is new construction and have rebar going around/inside with a piece sticking out for the ground.
The main box is 100 amp.
 
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  #2  
Old 05-23-06, 06:49 PM
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What's your definition of a basic welder? A 50A Lincoln 225AC or a 30A Millermatic 175?

With a main panel of 100A, a 50-60A sub is pretty much your limit anyway, as long as there are no big loads in the house at the time, like air conditioning.

By the way, all those things you listed are "outlets" Among the outlets that you need are 6 receptacles. I'd put them on two circuits.

If you stay with a 50A, you can use #8 wire. 60A will require #6. One size less for the ground.

I don't have the experience to address the issue of using the rebar for your grounding electrode.
 
  #3  
Old 05-23-06, 07:07 PM
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The rebar is a portion of the ground, but you probably also need a ground rod.
 
  #4  
Old 05-23-06, 07:14 PM
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so my research is paying off, so i should just stick with a 50 amp subpanel and 8 awg will be fine. I just plan on getting a mig welder to fabricate bumpers and hobby stuff. I have not researched the welder yet but will stay within my power range. thanks alot. Oh the rebar is approximately 200 feet in length imbedded in the slab, will that do?
 
  #5  
Old 05-24-06, 12:22 AM
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If you'd like help or ideas on the welder selection, take a gander over to www.hobartwelders.com, and join the Weld Talk forums. We discuss all machines and anything even remotely related. Love to have you.
 
  #6  
Old 05-24-06, 05:36 AM
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It is much easier to add a ground rod than to determine if the rebar is sufficient. You cannot make the determination without taking measurements using special equipment. Just add a ground rod and be done with it.
 
  #7  
Old 05-24-06, 11:52 PM
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Before we poured the concrete the inspector signed off the ufer and grounding (rebar), hopefully that is sufficient but if a rod is suggested than I will pound one in.
I just want to make sure before I buy the wire (expensive) that I have the right AWG for the subpanel.
three 8 awg feeder and one 10 awg for ground.
This size wire is good enough for 50 amp subpanel and will it pass code. Trying to get anything out of the city is hard.
 
  #8  
Old 05-25-06, 12:06 AM
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three 8 awg feeder and one 10 awg for ground.
This size wire is good enough for 50 amp subpanel and will it pass code

humm i am suprised with this one i dont know how you got there but if this is copper thwn wires genrally we like to keep limited to 40 amp breaker not 50 amp breaker due the termail connection ratings.

the reason why i am little lerry with this becaue the distance from the house breaker box to the garage subfeed box it can do some funny thing what we called voltage drop especally if you run hevey load like welder or big air commpressor you will see the light will ficker a bit if the wires are really undersized.

so just think it over before you buy it

Merci , Marc
 
  #9  
Old 05-25-06, 12:15 AM
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so i should step down to a 40 amp subpanel or increase thhn wire gauge to 1 up for 50 amp? I just want to make sure I can use a compressor and welder separetely once in a while.
 
  #10  
Old 05-25-06, 12:22 AM
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if you did not buy the wire yet ,, then you are lucky [ dont start with price of copper wires right now they are getting skyhigh ]

for 70 feet run i really recomoned to run #6 THWN wires with 50 amp breaker they cost little more but have better load crusion [ sp { sorry i try to find engish word for this }]

the 40 and 50 amp breakers useally cost about the same but the price of wires it will make the diffrence so better off use # 6 THWN [ it will be dual rated it will printed both THHN and THWN ]

so that way you dont have to worry if the breaker trip when you run the welder and the light going on the same time

Merci, Marc
 
  #11  
Old 05-25-06, 12:24 AM
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thanks alot for the info.
 
  #12  
Old 05-25-06, 04:40 AM
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If the run is in conduit the WHOLE way, you can use #8 on a 50 and #6 on a 70 amp breaker. Conduit with conductors has a slightly higher amperage rating than cable.
If you have ANY NM cable in this circuit you can use #8 on a 40 and #6 on a 60 amp breaker.
70' is not that far.

IMO I recommend #6 on a 60 amp breaker. No reason to go any lower. The price difference between #6 & 8 is not that great. Everything else is the same.
And if you have a signed off Ufer, use it. NO extra ground rod is required.
 
  #13  
Old 05-29-06, 12:02 AM
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I bought the wire, 8 was half the price of 6 and I needed 110 feet. The actual length was way more when I measured the distance. So with 8 awg feeder, what is the max main breaker size for the subpanel now? 40 or 50.
 
  #14  
Old 05-29-06, 05:36 AM
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The answer is still the same.

Originally Posted by Speedy Petey
If the run is in conduit the WHOLE way, you can use #8 on a 50 and #6 on a 70 amp breaker. Conduit with conductors has a slightly higher amperage rating than cable.
If you have ANY NM cable in this circuit you can use #8 on a 40 and #6 on a 60 amp breaker.
70' is not that far.
 
  #15  
Old 05-29-06, 05:54 AM
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I raised the feeder length to 110 feet instead of 75, I read somewhere about voltage drop, was just making sure the 8 awg is still good for 50 amp. thanks petey
 
  #16  
Old 05-29-06, 06:24 AM
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That's fine. 110' is not really that far for a feeder.

Even for a full 50 amps, #8, @ 110', @ 240v, voltage drop is only about 3.5% .
Well under the 5% limit for feeders.
 
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