wiring a workshop

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  #1  
Old 08-19-05, 01:26 PM
aerohead34
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wiring a workshop

I have a 100 Amp circuit breaker box in my workshop. I have done the basic wiring inside the shop to the box. I want to run 240V from my main panel outside my house to my workshop. I would like to start at the main panel with a double pole 50 Amp circuit breaker. I would then like to run 6-3 wiring from this circuit breaker to my workshop 100 Amp box. My questions are:
1) Since I am running 240 volts can I use the 55 Amp rated 6-3 wiring? I am thinking that would give me 2 50 Amp lines running into my workshop circuit breaker box making a total of 100 Amps service.
2) My second question deals with circuit breakers in general. Is a double pole 100 Amp circuit breaker rated for 100Amps at 120 volts and 50 Amps (each leg) at 240 volts? Thats my reasoning behind being able to use 55 Amp rated wire instead of 100 Amp?
 
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  #2  
Old 08-19-05, 02:00 PM
I
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Your understanding is a bit flawed. If you feed your garage subpanel with a 50A DP breaker and 6-3 cable, your garage has a 50A 240V service. What that means is you can run 50A worth of 240V appliances -or- 100A worth of 120V appliances (assuming they are roughly balanced in the panel).

You can safely supply up to 65A at 240V using a 6-3 feeder cable, assuming you have 75 degree terminations, which most panels do. You could therefore put a 60A DP breaker in your main panel to supply the sub. Staying with the 50A breaker, however is totally acceptable and may be required at the discretion of your local inspector.

Have you considered the multitude of code requirements with regard to grouding and bonding for subpanels in detached buildings?
 
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Old 08-19-05, 02:10 PM
R
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I am concerned about your lack of understanding of this fairly basic element of a sub panel. Please make sure that your work is inspected so that you don't start a fire or kill someone.

You have a 100 amp panel for the shop. That means 100 amps at 240 volts. If you use a 50 amp breaker at the main panel then you are limited to half the capacity of the panel, which may be sufficient for your needs.
 
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Old 08-19-05, 02:22 PM
aerohead34
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If I knew the answer to the basic question about circuit breakers, I wouldnt have had to ask here. The fact that double pole circuit breakers rating (100 Amps) is the same for each leg as the rating basically answers my questions. I have to decide whether I need 100 Amps of 240 volt power or 100 Amps of 120 volt is sufficient. I dont currently have anything in my shop that runs off 240. I am going to try to get an electrician come out and hook up my wiring to the main panel. Since this part of Alabama is growing by leaps and bounds, there's more money to be made in new construction than in existing homes or someone like me who cannot afford $1500 plus to let an electrician do everything. I have done basic wiring like adding outlets and adding ceiing fans and switches since I was a teenager. I have no problem laying out or doing the wiring to the workshop circuit breaker panel. Since I have no experience on the other side of the circuit breaker box, I needed help understanding.
 
  #5  
Old 08-19-05, 02:26 PM
R
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You still don't have it right.

With a 50 amp 2 pole breaker in your main panel and the correct wiring, you have 240 volts at your sub pabel in the shop.

Your decision is not between 120 volts and 240 volts. Your decison is between 240 volts at 50 amps (as you propose), 240 volts at 60 amps (as ipbooks suggested is the maximum for the cable) and 100 amps at 240 volts (which is the maximum you can do with this panel).
 
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Old 08-19-05, 02:35 PM
I
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A 60A service will be more than adequate for 95% of the home shops/garages out there, especially if there will only be one person working at a time.

I would only consider a 100A serivce if you plan to operate a welder with an air conditioner running, or if you plan on getting some seriously large power tools.

Please read this very complete guide on subpanels in detached garages. It will help you decide what you need, and explain many of the important codes.

http://www.selfhelpandmore.com/homew...arageshowp.htm
 
  #7  
Old 08-19-05, 02:52 PM
aerohead34
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The main breaker in the service panel is double pole and 240 volts. Right now I only have 5 single pole 20 Amp circuit breakers in the service panel going out to the workshop. I was only saying that I need to figure out whether or not I will have any equipment that runs on 240 volt and whether or not I need 100 Amps of 240 volt power (24000 watts power) or if 50 Amps (or 60 as ipbrooks suggested) of 240 volt (12000 watt power) is sufficient. Since there is significant expense going from 6-3 wire to size 2 or 0, I have a decision to make whether I will even need the extra capacity of my service panel. Right now, the workshop is wired for 120 volts. As I said before knowing how circuit breakers are rated (double pole) answered my main question.
 
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Old 08-19-05, 02:55 PM
aerohead34
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Thanx for the link. I will definitely check it out. I dont plan on having a/c or welding.
 
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