100 amp subpanel

[50cal]

I would like to get some input on a 100 amp subpanel installation. I have

searched this but could not find anything I felt was specific enough, I don't

want to buy the wrong stuff.

To start off I have a 400 amp service, 2-200 amp panels. I am going

approximately 80 feet out to existing garage. During new construction I buried

a 2 inch conduit under the floor and stubbed it out in the basement. I would

like to drop the size of conduit down to the bare minimum for the wire size.

So my two questions are what size wire and what size conduit do I need? I am

located in the midwest USA.

 

[pattenp]

For 100A, THHN/THWN #3 copper 1 1/4" PVC conduit, THHN/THWN #1 aluminum 1 1/2" PVC conduit.

Edit: You may not need a full 100A feed. Do you know your amp load requirements?




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[volleyball]

Why minimum size? Go big.

 

[Falcon67]

Stick with the 2" - it'll make whatever you pull that much easier.

 

[50cal]

I would like to get some input on a 100 amp subpanel installation. I have

searched this but could not find anything I felt was specific enough, I don't

want to buy the wrong stuff.

To start off I have a 400 amp service, 2-200 amp panels. I am going

approximately 80 feet out to existing garage. During new construction I buried

a 2 inch conduit under the floor and stubbed it out in the basement. I would

like to drop the size of conduit down to the bare minimum for the wire size.

So my two questions are what size wire and what size conduit do I need? I am

located in the midwest USA.

For 100A, THHN/THWN #3 copper 1 1/4" PVC conduit, THHN/THWN #1 aluminum 1 1/2" PVC conduit.

Edit: You may not need a full 100A feed. Do you know your amp load requirements?




*

One of the circuits is for a 250 amp tig welder that takes a 70 amp breaker to start a weld plus compressor, grinder on and on. There is a central vac in there to that is 220. When I wired the house I left all the home runs for the garage out there with this in mind.

The conduit, since I put that in there is a joist bay where a upstairs and basement heat run are one on top of the other and there is just enough room to get a 1 1/2 inch conduit in between without a severe dent. Floor trusses I dont want anything below them in this area.

I was thinking that the two phase conductors were the same and the nuetral and ground could be reduced? As in 3,3,4,6?

 

[volleyball]

Who is to say you cannot run a couple of smaller conduits where space is tight? That way you don't lose capacity which you seem to need/want.

 

[wyliesdiesels]

One of the circuits is for a 250 amp tig welder that takes a 70 amp breaker to start a weld plus compressor, grinder on and on. There is a central vac in there to that is 220. When I wired the house I left all the home runs for the garage out there with this in mind.

The conduit, since I put that in there is a joist bay where a upstairs and basement heat run are one on top of the other and there is just enough room to get a 1 1/2 inch conduit in between without a severe dent. Floor trusses I dont want anything below them in this area.

I was thinking that the two phase conductors were the same and the nuetral and ground could be reduced? As in 3,3,4,6?

Welders have different rules. It may require a 70a breaker but i HIGHLY doubt it uses that much juice. I would do load calcs. And im will to bet u could get by with a 60 or 70a feed!

 

[theoldwizard1]

One of the circuits is for a 250 amp tig welder that takes a 70 amp breaker to start a weld, plus compressor, grinder on and on. There is a central vac in there to that is 220.

Welders have different rules. It may require a 70a breaker but i HIGHLY doubt it uses that much juice. I would do load calcs. And im will to bet u could get by with a 60 or 70a feed!

The real question is, how many pieces of equipment are going to be running simultaneously. If you happen to strike an arc exactly at the time the compressor is starting, you might trip a 70A breaker protecting the feed wire.

Just because you are using a 100A breaker panel in the garage does not mean that the feed wire and the breaker protecting that wire also have to be rated at 100A.

 

[volleyball]

The real question is size of conduit, not how much service is needed.

 

[50cal]

For some reason I haven't been getting alerts that there were posts here.

The welder is a 250 amp Hobart that can be used to do stick and tig also has

hi frequency built in for aluminum. A 60 amp breaker wont hold it in

hi frequency.

I want to go with 100 amp sub so there will not be a capacity problem in the

future. I just need to know what size wire to buy to be at code and keep the

inspector happy. I planned to put a 100 amp breaker in the main service

panel.

Would 3 3 3 copper work for this? What size ground? Can I reduce the size of

the neutral?

 

[pattenp]

For 100A a #8 Cu is minimum for the equipment ground. For no good reason I'd use a #6. As I said earlier, #3 THHN/THWN Cu is good for 100A. If you use aluminum you need #1. If you use copper you can do the 3-3-4-6 combo as you asked about before. But for the few dollars more I'd do 3-3-3-6. I don't seen any advantage to reducing the neutral other than saving a few bucks.

 

[50cal]

For 100A a #8 Cu is minimum for the equipment ground. For no good reason I'd use a #6. As I said earlier, #3 THHN/THWN Cu is good for 100A. If you use aluminum you need #1. If you use copper you can do the 3-3-4-6 combo as you asked about before. But for the few dollars more I'd do 3-3-3-6. I don't seen any advantage to reducing the neutral other than saving a few bucks.

Thank you, I am going to run the conduit this weekend.