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AZ_Engineer · Jun 24, 2007, 07:19 PM

I have a subpanel in the garage that is connected to the main panel on the side of the house. The current line is 4 gauge copper and runs about 50 ft. The current subpanel is fed by a 50amp 220v breaker. I'd like to be able to add a split unit AC to the garage that would pull 20amps, and I use heavy toold that can require up to 50 amps. Can the 4 gauge 50 foot run handle more amperage per code? If I have to rewire, what gauge do I need for 100amp? Also, the way it is currently wired, I have the main on the side of the house running to a sub panel in the garage. Is it OK per code to have a sub panel feed another sub panel assuming all are breakered properly?

Note, the garage and house are attached, and I an running ground from the garage to the main panel and using a common earth ground.

I'd love to not have to retrench and put in new conduit and cable, but safety is most important to me... joe

tkrussell · Jun 25, 2007, 01:57 AM

#4 copper is allowed by code to be used as a residential 100 amp feeder. Yes, a sub panel can feed a sub panel.

AZ_Engineer · Jun 26, 2007, 01:26 PM

Originally Posted by tkrussell

#4 copper is allowed by code to be used as a residential 100 amp feeder. Yes, a sub panel can feed a sub panel.

Thanks, this is great news.. joe

AZ_Engineer · Jun 26, 2007, 05:48 PM

Originally Posted by tkrussell

#4 copper is allowed by code to be used as a residential 100 amp feeder. Yes, a sub panel can feed a sub panel.

I have an alternate idea. The heatpump for my home is a 5 ton unit that is served by a safety switch with a 60 fuse in it. I haven't checked the wire gauge feeding that switch, but the 5 ton unit only draws 42a according to the plate on the side of the 5 ton compressor unit.

Could I use that one 60amp safety switch to supply the existing heat pump, and the a mini-split unit. (This is what I'm really looking to add to the garage). If I could supply the minisplit with up 18 amp, I think it would cheaper and easier to do it this way.

Thanks... joe

tkrussell · Jun 27, 2007, 02:53 AM

Sorry, but no. Branch circuit wire and overcurrent protection devices for HVAC are sized differently than anything else, due to the inherent characteristics of high locked rotor amperages. The net gain of amps you see is not there as it it reserved for starting the unit. Trust me, if you combine the two units on this one circuit you will have problems.