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Old 11-24-2012, 07:49 PM   #1
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Which gauge do I use?


Hello all, I have what may be just a simple question but I'm having trouble finding the answer at my locale home improvement store. I am building a new workshop behind my house and I am trying to see what gauge wire I can get away with safely as wire is costly. My situation is this, My building will be about 50' from the main box location if that. I want to run the line from the box to a second box I will install in the shop, from there I will run 12-2 throughout. I only plan to have a small 70amp 110v welder, a bench grinder, a fridge, air compressor, a few florescent lights and 6 or 7 receptacles in all. One man told me to run 8-3, another 4-3, and another said run two 10-2's. I was looking to purchase a 100amp indoor box with a main along with my wire. Any and all advice is appreciated and I suppose my basic objective is to keep the cost down while still being safe. I know a fair amount of this but I would like a real pros advice.

p.s. I also realize the line should only carry 80% of the load.

Thank you.

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Old 11-24-2012, 08:01 PM   #2
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Which gauge do I use?


First add up all of the wattages of your known equipment from the nameplates on the equipment and let us know what that number is.

The size of the wire needed will be determined by the size of the breaker feeding your sub panel.

If you can get away with less than a 100 amp feed, you can use a smaller wire.

I believe 100 amp feed will need a 2-3 + ground NM (copper) or size 1/0 aluminum (3+ground).

Someone will correct me if I'm wrong.


Last edited by TTW; 11-24-2012 at 08:09 PM.
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Old 11-24-2012, 08:07 PM   #3
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Which gauge do I use?


#4 wire will allow you a 80 amp. service. Can you bury conduit or are you hell bent on using cable? If you bury conduit you have a bit of flexibility in case your needs change. With the price of wire nowadays this isn't going to be a cheap install at any rate.
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Old 11-24-2012, 08:57 PM   #4
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Which gauge do I use?


Thank you both for the quick reply. My total wattage is about 5000 watts including lights. As far as cable vs. wire with conduit I have no preference and I can use either. I do realize the it isn't going to be cheap and I can and will spend the money, I am just trying to see what is the cheaper way to go, at the store I just felt like they were trying to sell it all to me.
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Old 11-24-2012, 09:16 PM   #5
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Which gauge do I use?


Quote:
Originally Posted by NQBQDY
My total wattage is about 5000 watts including lights.
Your welder alone appears to exceed 5K watts...

Last edited by jlmran; 11-24-2012 at 09:19 PM.
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Old 11-24-2012, 09:18 PM   #6
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Which gauge do I use?


Oh sorry this is just what I was going by:

120 volt, 20 amp, single phase input
Thermal overload protection with indicator light
Welding current: 40-70 amps AC
Rated duty cycle: 20% @ 70 amps
Stepless current regulator
Input: 120 volts, 20 amps, single phase, 60 Hz
Welding current: 40-70 amps AC
Rated output voltage: 22
Max open circuit voltage: 42
Rated duty cycle: 20% @ 70 amps
Electrode capacity: 1/16" to 3/32"
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Old 11-24-2012, 09:21 PM   #7
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Which gauge do I use?


Ahhh...welding current. Thought that was a bit strange, the way you had it worded.
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Old 11-24-2012, 09:21 PM   #8
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Which gauge do I use?


I would suggest running PVC and individual (3) #6 THHN/THWN and a #10 CU ground on a 2 pole 60A breaker.
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Old 11-24-2012, 09:27 PM   #9
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Which gauge do I use?


to jlmran: yeah I didn't word it right but didn't realize until you said something, sorry.

to k_buz: thanks I never really thought of running them individually.
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Old 11-24-2012, 09:30 PM   #10
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Which gauge do I use?


I'm going to ask you a few questions and post some diagrams for you to use as a guide line.

Is your homes service 100 amps and if it is what big electric appliances are you operating if any ...ie... electric stove, central ac, baseboard heat etc.

Based on your description disregarding the welder which I think is incorrect at 70 amps you would get by fine on a 60 amp feeder to your 100 amp shop panel. However it is prudent to determine how tasked your homes panel is before adding load to it from your shop.

Assuming you have 150 amp or bigger service my opinion would be to run a 70 amp 4 wire feeder using three 6 awg thhn/thwn individual wires and one #8 ground in 1 1/4 " PVC. Protect it with a 70 amp double pole breaker in your homes panel. The 100 amp main breaker panel for the shop is a good choice and will satisfy the requirement for a service rated disconnect located at the shop. The shop panel need to be mounted as close as possible to where your feeder enters .. also a code requirement. The pvc needs to be 18" deep measured to the top of the pipe. Your shop panel needs to have the neutral and ground separated. Study these drawings and if you have questions use them as reference.
Attached Thumbnails
Which gauge do I use?-subpanel-2.jpg   Which gauge do I use?-feeder-sub-panel-1.jpg  

Last edited by Stubbie; 11-24-2012 at 09:49 PM.
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Old 11-24-2012, 09:32 PM   #11
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Which gauge do I use?


to k_buz: I was thinking of having 220v at first, but everything I have in there will be 110v, is it better to have it anyway just to carry a load?
this probably seems funny and foolish but originally I was just going to run a 10-2 line off of a 30 amp breaker from my supply box. I now am glad I sought out help.
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Old 11-24-2012, 09:40 PM   #12
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Which gauge do I use?


Quote:
Originally Posted by NQBQDY View Post
to k_buz: I was thinking of having 220v at first, but everything I have in there will be 110v, is it better to have it anyway just to carry a load?
this probably seems funny and foolish but originally I was just going to run a 10-2 line off of a 30 amp breaker from my supply box. I now am glad I sought out help.
Not really foolish but if your going to weld and have a compressor I'd say the minimum would be 40 amps. After all this is a shop not a garage.
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Old 11-24-2012, 09:43 PM   #13
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Which gauge do I use?


Quote:
Originally Posted by NQBQDY View Post
Oh sorry this is just what I was going by:

120 volt, 20 amp, single phase input
Thermal overload protection with indicator light
Welding current: 40-70 amps AC
Rated duty cycle: 20% @ 70 amps
Stepless current regulator
Input: 120 volts, 20 amps, single phase, 60 Hz
Welding current: 40-70 amps AC
Rated output voltage: 22
Max open circuit voltage: 42
Rated duty cycle: 20% @ 70 amps
Electrode capacity: 1/16" to 3/32"
The red high light is the one your interested in ...
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Old 11-24-2012, 09:49 PM   #14
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Which gauge do I use?


I first want to say thank you to everyone, secondly I want to apologize I feel my original post might be misleading and worded wrong. I would like to start over, I intend to build a 16' x 16' shop/shed and would like to add power to it. My home box is a 200 amp panel which will be roughly 50' from said shop. I will have 4 florescent hanging lights, say 8 2-plug receptacles, bench grinder, welder, a fridge, air compressor, and a battery charger for cordless tools. I'm not sure if this is any more helpful or just confusing.
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Old 11-24-2012, 09:51 PM   #15
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Which gauge do I use?


I only intended to add a box to allow me to split the load among a few breakers instead of one big breaker at the house panel.

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