New 100A sub panel questions on gauge and codes.

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  #1  
Old 08-06-14, 08:51 PM
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New 100A sub panel questions on gauge and codes.

I have a 200A main panel on my house built in 1991. It's totally full, but i changed to a gas stove so I could remove a 40A 220 breaker. There is another 30A 220 drier outlet that I dont use because I have a gas drier. I figure that it would be fine to remove both of those and replace them with a 70A feed to a new workshop that I'm building. I'm hoping that I could add 100A instead because the reality is that the house breakers are way overkill for most rooms. I think every room is on it's own circuit (there are 30 breakers!) Going to a 400A panel is not in my budget because I need larger conduit off the main drop, new concrete, etc, and I'll never come close to pulling 200A.
  1. Does anyone see any problem with running a 100A breaker to replace a 40 and 30A?
The will be around 100' under my house to a junction box to a junction box on the outside of my house. From there it will need to go into couduit underground for ab out 25' to a new workshop that is yet to be built. It will come up through the slab to the 100A panel inside the shop.

I have a number of 220V tools, but they will never be used at the same time because it's just me in there. I have an old welder that can pull 80A @220v, but that is for welding 1" and I probably wont do that. I ran everything at my last house on a 40A circuit and I never popped it. I will also have a 40A on demand hot water heater that will provide hot water to the shop. The other 220v tools are another welder, vacuum, table saw, and a car lift.

Someone told me that I could run some kind of wire that comes in conduit under the house. I'm wondering if I even need conduit under the house. The rest of the large wires under there are not in conduit.
  • Is there some sort of newer code that requires conduit under the house?
  • It seems that the length of the run doesn't matter for the wire gauge with AC. Is that true?
  • I was thinking about running 4 x 2 gauge wire (2 hots, neutral and ground). Is that too much, or not enough gauge?
  • What size conduit should I run underground? I assume PVC is ideal. True?
I've done lots of electrical work, but I want to make sure that this is all legit, and could pass code if needed. Any tips, advice, etc will be much appreciated.
 
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Old 08-06-14, 08:58 PM
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Welcome to the forums.

How do you run conduit UNDER the house ?
Most times it's run around the house. PVC conduit is fine.

You can put a 100A two pole breaker in place of one of the non-used breakers.
 
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Old 08-06-14, 09:06 PM
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Thanks! The house is a subfloor so I have between 6' and 2' to deal with.
 
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Old 08-06-14, 09:25 PM
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your 200 amp service should be fine.


Does anyone see any problem with running a 100A breaker to replace a 40 and 30A?
no

Is there some sort of newer code that requires conduit under the house?
no.....................but pvc conduit is very nice.

..........pvc conduit all the way with THHN wire...hang the pipe under the house..........
.3#4 and 1#6 ground go underground as you leave the house......no J-BOX.....1 1/4 or 1 1/2 inch pipe.

run the 4-wire circuit to a sub panel in the shop.
 
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Old 08-07-14, 06:19 AM
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pvc conduit all the way with THHN wire...hang the pipe under the house..........
.3#4 and 1#6 ground go underground as you leave the house......no J-BOX.....1 1/4 or 1 1/2 inch pipe.

run the 4-wire circuit to a sub panel in the shop
.

For a 100 amp feeder to the garage, I'd use either 3 - #3 copper THHN/THWN and 1 - #8 copper THHN/THWN ground....OR....3 - #1 aluminum XHHW and 1 - #6 aluminum XHHW ground in 1 1/2" conduit.
 
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