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Wiring detached garage for 240 V, 53 amp welder, receptacles, lighting, etc

Wiring detached garage for 240 V, 53 amp welder, receptacles, lighting, etc

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  #1  
Old 04-25-11, 09:40 AM
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Wiring detached garage for 240 V, 53 amp welder, receptacles, lighting, etc

I would appreciate some help with a wiring project -- new service for my detached garage (primarily, wire and breaker size).

In the detached garage I will have an old 240 V welder (53 amp input), two 120 receptacles for small tools (up to 15 amps), lighting and door opener.

The main disconnect panel is about 40 feet away and located on the inside of my attached garage. The Poco meter is on the outside wall and opposite this panel.

I have purchased 1 1/4" rigid conduit to connect the main panel and the detached garage subpanel.

Some of the things I know: Use thwn wire for wet locations. Bury the conduit below 6" and run it from both points of entry. Inside, use EMT. Separate the neutral and ground in the subpanel and do not bond the ground with the panel box. Use main lug type subpanel. I have been told I should not use a grounding rod at the subpanel due to the fact that the main panel rod is so close.

My Questions: Breaker size for both Main and Sub panels. Wire size in copper and aluminum for hots, neutral and ground.

I would also like to know if I can run the wires from the main panel back through the hole where the wires from the meter come in. From there I would enter the 1 1/4 conduit. This would save having to put another hole in the side of my house.

Thanks
 
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  #2  
Old 04-25-11, 09:56 AM
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Originally Posted by RobCab View Post
In the detached garage I will have an old 240 V welder (53 amp input), two 120 receptacles for small tools (up to 15 amps), lighting and door opener.
Do you know the duty cycle for the welder? How about the make/model? Need to know these to pick the correct wire size.

I have purchased 1 1/4" rigid conduit to connect the main panel and the detached garage subpanel.
Galvanized threaded rigid metal thickwall conduit? Officially called RMC (rigid metal conduit)?

do not bond the ground with the panel box.
The ground is bonded to the panel box. The neutral is not.

Use main lug type subpanel.
A main lugs panel is only allowed if there are 6 or fewer breakers in the garage, otherwise a main breaker panel is required.

I have been told I should not use a grounding rod at the subpanel due to the fact that the main panel rod is so close.
Ground rods should be installed at the garage. Distance between outbuildings is not mentioned in the code.

I would also like to know if I can run the wires from the main panel back through the hole where the wires from the meter come in.
No, the conduit must be continuous from panel-to-panel.
 
  #3  
Old 04-25-11, 02:19 PM
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Thanks for the information. Very helpful.

The conduit is rigid (threaded and $32 per 10' length).

Welder is "Duty Cycle 100% tapering to 20%".

I would want to have the least number of spaces in the panel. For example, two spaces for the 240 V welder receptacle, one space for the 120 receptacles and one space for the lighting and door opener. I don't know what this would mean in terms of wire size and breaker size.
 
  #4  
Old 04-25-11, 02:47 PM
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Originally Posted by RobCab View Post
The conduit is rigid (threaded and $32 per 10' length).
Okay, just wanted to make sure for the 6" burial depth.

Welder is "Duty Cycle 100% tapering to 20%".
Sounds like about a 70A subpanel would be sufficient for your needs, but you could certainly do up to 100A if you wanted room for future expansion. The minimum sizes I would do for 70A is copper THHN #6 black for the hots, #8 white for the neutral, #8 green/bare for the ground. The option for aluminum XHHW would be #4 black for the hots, #6 white for neutral, #6 green/bare for the ground.

Post back if you would like info for a larger panel size.
 
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Old 04-25-11, 04:04 PM
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I would like the info for the larger 100A panel if you don't mind. Also, are the THHN and XHHW both suitable for wet locations? Thanks. This has been really helpful.
 
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Old 04-25-11, 04:18 PM
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are the THHN and XHHW both suitable for wet locations?
I believe ibpooks meant THHN/THWN. The "W" signifies wet location for both types. Wire size would be 3,3,4,8 copper or 1,1,2,6 aluminum. Ground optional.
 
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Old 04-25-11, 08:28 PM
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Much obliged Ben and Ray. -- Robert
 
  #8  
Old 04-26-11, 08:44 AM
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Originally Posted by ray2047 View Post
I believe ibpooks meant THHN/THWN. The "W" signifies wet location for both types.
Yep, most (probably all) THHN is also rated THWN-2. I just said the wrong one.

Ground optional.
To clarify a little on what Ray said. The steel conduit can be used as a ground instead of the green/bare wire as long as the metal pipe is continuous from panel-to-panel (no plastic parts) and it is securely fastened to the metal panel boxes (lock nuts, bonding bushing). The ground rods and unbonded neutral are required whether you choose to install the ground wire or not. I prefer to install the ground wire because it is much less susceptible to corrosion than the pipe.
 
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