Help with wire/sub panel/correct breaker

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  #1  
Old 05-18-14, 08:29 PM
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Help with wire/sub panel/correct breaker

Need help!!

Project:
take electricity to workshop which will power air compressor (.Voltage: 208-230/460 Volt AC) and numerous tools commonly used in automotive repair and body repair

Workshop: 24X36

Main residence: Main panel - main breaker 200 amp fuses (4)

Current setup: There is a three strand wire (THHN 10 AWG) coming from the main panel attached to 20 amp breaker. The proper pipe is used from the Main panel to the exterior of the residence. There is a junction box at the exterior of the house. From that point there is under ground piping to a point of the workshop where is terminates inside and a sub panel was installed. The sub panel is not active at this time. A grounding rod will be installed.

Distance from each other approximately 70'

Question: In looking at the Main panel and seeing one vacant slot. I want to know if I can move the 2nd breaker currently situated below the one marked "storage" and next to the vacant blocked slot, up to the storage slot along with its wires.
That would give me two slots side by side therefore possibly allowing me to place a 60 amp ( or larger...please advise) so that it would supply enough power to run the Air compressor plus other tools/lights without tripping a breaker in the main panel. I would of course replace the 10 wire with a 6 (?).

If I am correct in this scenario I would not have to ground the sub panel in the garage(?).

Please let me know y'all's recommend. Thanks !!

I have attached a picture which shows the breaker used to power the wire going out (blue tape) and the Main breaker...
 
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Old 05-18-14, 09:06 PM
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Welcome to the forums.

Yes.....you would have to replace the #10's with #6's. Is the conduit large enough to support the increased wire size ? If the garage is a detached garage then you will need to ground the sub panel.

If that air compressor motor also has 460v as a wiring choice then it must be a pretty good sized motor. What does the nameplate say the amperage draw is at 208-230v ?

http://www.doityourself.com/forum/el...-pictures.html
 
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Old 05-18-14, 09:21 PM
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The conduit is large enough. The guy at Home Depot said I need four wires...there are currently three. I will ground the sub panel, I have the rod, wire and clamps already.

You think my swapping the breakers in the Main panel to get a bigger breaker in there will work?

The compressor is on its way. I am only guessing the compressor will need 30 amps. It has a 15 hp motor.
 
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Old 05-18-14, 09:25 PM
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This is the main panel showing the vacant/blocked off space
 
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Old 05-18-14, 09:37 PM
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You are in trouble for breaker space. That black blank is a half space blank. Your new two pole breaker will be two full spaces like the others currently in your panel.
 
  #6  
Old 05-19-14, 12:02 AM
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That air compressor you have ordered has a three-phase motor yet you only have single-phase power in that service panel. You cannot run a three-phase directly from a single-phase supply. Further, at 240 volts you will need a minimum of 42 amperes, again at three-phase. To make this worse, it is unlikely that the motor is a star (wye) winding and that precludes the use of a fairly simple phase converter, you will need a rotary converter and THAT will take up to 63 amperes at 240 volts all by itself. Add in the other loads and you are looking at some pretty husky wiring, exactly what size conduit is now in place? I would use an absolute minimum of #4 copper conductors and that requires a one inch PVC conduit at minimum.

Something else to consider is a whole new service from the utility and if possible a three-phase service. Unfortunately a three-phase service may not even be available, especially if the shop is in a residential area. What are you going to be doing in this shop and if in a neighborhood zoned for residential will you be in a non-compliant situation with the local government?
 
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Old 05-19-14, 07:20 AM
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You are in trouble for breaker space. That black blank is a half space blank. Your new two pole breaker will be two full spaces like the others currently in your panel.
The needed breaker would be a THQP 2 pole 60 amp and they are available and not a problem. The THQP is the thin series in a 1" format.

Relectric.com: THQP260 - General Electric / GE Circuit Breakers

The problem is as Furd mentions, the compressor has a 3-phase motor and cannot be powered from a single phase panel. You'll not easily find a 15 HP single phase motor, I don't think they are even available.
 
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Old 05-19-14, 05:06 PM
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The largest single-phase motor I have ever seen was 7-1/2 horsepower, I may have read about a 10 horsepower one many years ago. He may also have a problem with the utility with that motor as many simply do not have the distribution in a residential area to support that kind of horsepower.
 
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Old 05-19-14, 07:13 PM
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The largest single-phase motor I have ever seen was 7-1/2 horsepower
Same here and they are rare.

He may also have a problem with the utility with that motor as many simply do not have the distribution in a residential area to support that kind of horsepower.
That's a definite!
 
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