Rewiring house, garage subpanel question

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Old 09-28-10, 03:21 PM
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Rewiring house, garage subpanel question

Okay. I'm planning on rewiring my house, and the I'll be applying for the permit next week. My neighbor had thought he had a 200A panel I could have from some cottages he has up north, but it turns out he just has 100A panels, so for the time being I'm not planning to upgrade my 100A panel in the house. I do want to run a 100A panel in the garage eventually, and for the time being I would run a smaller panel in the garage but for the time being I'd like to run the cable to the garage that will be large enough to upgrade later.

What kind of panel could I put in the garage for now, preferably under $50... If it's going to cost close to $95 or even half of that, I might as well just buy the 200A panel for the house and put the current 100A panel in the garage, but I want to see if there's something less expensive that I could use for now (or if I could use the free 100A panel from the neighbor, even though that would be a 100A running off a 100A main breaker..)
 
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Old 09-28-10, 03:35 PM
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I do not recommend re-using old panels unless they are reasonably new and in exceptionally good condition. The amount of labor and ancillary expenses that goes into a service upgrade makes it worth getting a new panel.

You will run into a problem of using a 100A panel in the garage with 200A wire because 200A wire will not fit in a 100A panel. The cost of adapting it will be more than just getting a 200A panel from the start. By the way, a 200A panel (48kW) is a huge amount of power that is almost certainly unnecessary unless this is a commercial garage. If you do a demand load calculation on the garage I'm sure you'll find 100A is more than enough.
 
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Old 09-28-10, 04:49 PM
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your misunderstood the OP i belive he said he wants the 200 amp panel in the house and 100 amp in the garage and for the time being he wants to install a smaller panel in the garage but size the wire for 100 amp....


well what i would do it run the 100 amp panel to the garage size it to 100 amp but use a breaker say 40 or 50 amps on it untill the house panel is upgraded to the 200 amp service
 
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Old 09-28-10, 08:49 PM
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That's correct, my intent is long-term I want to end up with 100A service in the garage. I am expecting eventually to get a TIG welder. The 100A service in the house is fairly recent.. I know it's less than 15 years old, I can't remember when it went in from the permit label on the inside, I have a bunch of dates floating around in my head of upgrades on the house in the last 5 to 15 years - heater, water heater, service panel.

So I just wanted to be sure if I get a 40 or 50 amp breaker it can take the #4 aluminum wire I need for 100 amps?
 
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Old 09-28-10, 10:03 PM
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4 awg aluminum is no longer acceptable for 100 amps. Im pretty sure and others will know for sure but I think the 4 awg is only good for 70 amps you would need to go with 2 awg or 4 awg copper

Remember you need 3 conductors and a ground Romex, UF or in conduit there is nothing wrong with feeding a 100 amp panel directly off another 100 amp panel even so if you wanted to avoid the cost of buying a extra breaker you could go with the full size breaker now but if your going to upgrade obviously you would need to get the same brand of panel so I guess in that respect you have a little deciding to do
 
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Old 09-29-10, 09:01 AM
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Originally Posted by WillK View Post
That's correct, my intent is long-term I want to end up with 100A service in the garage.
Ahh okay, I misunderstood that.

So I just wanted to be sure if I get a 40 or 50 amp breaker it can take the #4 aluminum wire I need for 100 amps?
100A requires minimum #3 copper or #1 aluminum (one size larger if using NM or SER cable). #4 aluminum maxes out at 55A or 65A depending on the exact type of wire.

No the 40 or 50A breaker probably will not take the large conductors. You'll need to use short pieces of smaller wire from the breaker and splice them to the large conductors with split bolts and tape or Polaris connectors. The price of making those connections might make it worth it to just get the panel/breaker you need upfront.
 
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Old 09-29-10, 10:14 AM
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I'm sure it's just some confusion on my part on terminology, I know it's a 4 in the term, I think it's 4/0 cable with 3 wires and a ground, I plan on getting it at Home Depot and it's the one they show as being appropriate for 100A service. They carry the aluminum in stock, the copper wire would be special order.

At any rate, actuall I forgot one of the key pieces of info on my plans. I'm also wanting to move the house panel to the utility room, this puts it closer to the pole, closer to the garage (shorter run for the 100A sub-panel) and gets it out of my bedroom, plus makes it a little more convenient to wire everything for the rewiring and still have lights from the old service in the mean time.

And it is my plan to bury the cable inside conduit. Being a car guy, I'm inclined to prefer PVC because I don't believe there exists a metal or coating that isn't going to and subsequently deteriorate, so where I can I feel better burying plastic rather than metal.

But if I can get 2 free 100A panels and a 100A subpanel running off a 100A main panel might be okay (I'll check with the inspector) I might be able to put off the $95 for the 200A panel, but then again if I'm having the power company move the incoming wire, I probably should just go ahead and go up to 200A at the same time.
 
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Old 09-29-10, 10:45 AM
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Originally Posted by WillK View Post
I'm sure it's just some confusion on my part on terminology, I know it's a 4 in the term, I think it's 4/0 cable with 3 wires and a ground, I plan on getting it at Home Depot and it's the one they show as being appropriate for 100A service.
Don't trust that chart at Home Depot! It does not take into account temperature ratings that the code requires and most of the listed ampacities are therefore wrong for anything except residential main services. #4/0 cable would be appropriate for a 200A residential service, the sizes I listed above are for 100A subpanel feeder.

And it is my plan to bury the cable inside conduit.
If you're using conduit, it's much better to pull individual conductors. A cable assembly is not flexible and will be a chore to pull or will tear the insulation. I would use three #1 alumiunum XHHW conductors for hot, hot, neutral and #4 aluminum for the ground. They usually don't stock this type at the big box, but you can easily pick it up at an electrical supply house.

I'm inclined to prefer PVC
PVC is the industry standard for underground. You'll want to go with at least 1-1/4" for 100A but bigger is easier to pull.

100A subpanel running off a 100A main panel might be okay
That is allowed.

if I'm having the power company move the incoming wire, I probably should just go ahead and go up to 200A at the same time.
It is almost always best to do all of the service work at the same time. If you want to go to 200A it would absolutely be the time to do it when you relocate the panel.
 
 

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