What wire to use?

[triplethreat]

Okay here goes. I've got a attached via a 54 foot long breezeway, 2 story garage plus attic . I've got two 200 amp panels in the house. The one panel is lighlty loaded so I want to install a 100 amp breaker in it and run 4 wires from the breaker to a 100 amp panel in the garage. Since the wire is running in the attic of the breezeway how do I do it? The panel in the garage will also have a 100 amp breaker for safety. I was plannning on running 4 wires through pvc conduit but not sure that will work cause of the heat in the attic. I saw in the code book where 122 degrees was the max for pvc. Does this mean I need to use a service type entrance wire and no conduit? If I used THNN /THWN I was going with 1 gauge or 1/0 copper to cover distance voltage drop and derating cause of temp. I'm also a bit into over kill. Length of wire estimated 85 feet. I'm a fan of copper and it seems most SER wire is Aluminium. All advice welcome.

 

[Aceman]

Okay here goes. I've got a attached via a 54 foot long breezeway 2 story garage plus attic . I've got two 200 amp panels in the house. The one panel is lighlty loaded so I want to install a 100 amp breaker in it and run 4 wires from the breaker to a 100 amp panel in the garage. Since the wire is running in the attic of the breezeway how do it do it? The panel in the garage will also have a 100 amp breaker for safety. I was plannning on running 4 wires through pvc conduit but not sure that will work cause of the heat in the attic. I saw in the code book where 122 degrees was the max for pvc. Does this mean I need to use a service type entrance wire and no conduit? If I used THNN /THWN I was going with 1 gauge or 1/0 copper to cover distance voltage drop and derating cause of temp. I'm also a bit into over kill. Length of wire estimated 85 feet. I'm a fan of copper and it seems most SER wire is Aluminium. All advice welcome.

Yes, there is a 122 degree limitation on pvc. I've never looked myself, but maybe the conduit is stamped with a higher rating? Is the run exposed? If it's not, I'd run the SER without conduit, it'll be much easier. They do make copper SER, a decent electrical supply house can get it for you.

 

[walrus]

You can upsize the wire if you want but whats the load going to be? If it isn't 100 amps I doubt upsizing is going to do much for ya except empty your wallet.

 

[triplethreat]

Is it okay to run copper service wire through the attic and several feet into both buildings?
Why is service conductor wire smaller then branch or feeder wire sizes? 100 amp breaker can use 2 gauge alum service wire but a branch circuit of 100 amps needs 1/0 Al or 2 gauge CU?? Can you hook the service wire up to a 100 amp breaker in a 200 amp panel and then run that to the panel in the garage?

 

[bimmer1980]

it's the difference between service wire and brach circuits. Generally, a service wire will not necessarily be fully loaded. You might have 100 amps worth of circuits (20's, 15's, 30's etc), but generally they will not all be loaded at the same time. You might only have 40 to 50 amps running at any given time. In a branch circuit, if you're running an air compressor, etc, you could very easily be running near the capacity of the wire at a much higher duty cycle. This "heats" up the wire and limits the current running thru it. So the NEC will allow a slightly smaller wire for service entrances as compared to branch circuits....... at least that's my understanding of it.....

 

[thammel]

"Can you hook the service wire up to a 100 amp breaker in a 200 amp panel and then run that to the panel in the garage? "

The other answers on why larger wire for the service breaker vs branch circuits are right on. On the above, definitely, yes. This is exactly what is the case for my garage and many subpanel installations, in general. For my garage, I have a 100 amp breaker in my 200 amp main panel. SE cable is connected to this and runs to the subpanel in my garage (probably close to an 90 foot run). I have a 100 amp subpanel in the garage with a 100 amp breaker in it, to which the SE is connected. In my case (and in most cases I'm aware of, for cost alone) aluminum SE cable is used.

I'd be inclined to run the SE cable in the attic of the breezeway and not in conduit. Are you planning to have an open attic or enclosed? It would look better from the underneath with a ceiling (i.e., enclosed) but would be a lot cooler and extend the roof life if it were open. I guess this also depends on whether this will be an enclosed or open breezeway (what the code requires and what you want), In any case, SE is used all the time for exterior open runs. If you're concerned about temperature, the best approach would be a buried run, but then you're talking trenching and that hassle.

Tom

 

[rinny_tin_tin]

Okay here goes. I've got a attached via a 54 foot long breezeway, 2 story garage plus attic . I've got two 200 amp panels in the house. The one panel is lighlty loaded so I want to install a 100 amp breaker in it and run 4 wires from the breaker to a 100 amp panel in the garage. Since the wire is running in the attic of the breezeway how do I do it? The panel in the garage will also have a 100 amp breaker for safety. I was plannning on running 4 wires through pvc conduit but not sure that will work cause of the heat in the attic. I saw in the code book where 122 degrees was the max for pvc. Does this mean I need to use a service type entrance wire and no conduit? If I used THNN /THWN I was going with 1 gauge or 1/0 copper to cover distance voltage drop and derating cause of temp. I'm also a bit into over kill. Length of wire estimated 85 feet. I'm a fan of copper and it seems most SER wire is Aluminium. All advice welcome.

You say its a breezeway yet it has an attic: "Since the wire is running in the attic of the breezeway ..."

Is it really an "attic" ?

 

[triplethreat]

My "Breezeway" is basically a 4 foot wide open on the sides connector between the house and the garage. It will be enclosed on the ceiling portion which is where I plan on running my service wire. I'm guessing one calls this the "attic" space not sure what else to call it. In Harford County Maryland since my garage is bigger then 50 percent of the square footage of my house it needs to be connected to the house to allow for a bigger garage. Thanks for the replies. My local electric supplier quoted me 1.65 a foot for AL SER 2/0 wire and 1.83 for 1/0 which seems really wierd. Guess I'm going with the 2/0 wire since its cheaper?? Not sure why the bigger stuff is cheaper unless it has to do with supply and demand. Hey Tom they just poured my floor today. I'm guessing they will put the steps to the second floor in on Monday.

 

[rinny_tin_tin]

My "Breezeway" is basically a 4 foot wide open on the sides connector between the house and the garage. It will be enclosed on the ceiling portion which is where I plan on running my service wire. I'm guessing one calls this the "attic" space not sure what else to call it. In Harford County Maryland since my garage is bigger then 50 percent of the square footage of my house it needs to be connected to the house to allow for a bigger garage. Thanks for the replies. My local electric supplier quoted me 1.65 a foot for AL SER 2/0 wire and 1.83 for 1/0 which seems really wierd. Guess I'm going with the 2/0 wire since its cheaper?? Not sure why the bigger stuff is cheaper unless it has to do with supply and demand. Hey Tom they just poured my floor today. I'm guessing they will put the steps to the second floor in on Monday.

I'm going to guess that your AHJ will rule that ceiling area of your breezeway is not considered an attic and thus the temp concerns are not applicable. I also have a breezeway with power cables running through the breezeway ceiling joists and the AHJ here made no mention of attic/temp issues.

 

[walrus]

My "Breezeway" is basically a 4 foot wide open on the sides connector between the house and the garage. It will be enclosed on the ceiling portion which is where I plan on running my service wire. I'm guessing one calls this the "attic" space not sure what else to call it. In Harford County Maryland since my garage is bigger then 50 percent of the square footage of my house it needs to be connected to the house to allow for a bigger garage. Thanks for the replies. My local electric supplier quoted me 1.65 a foot for AL SER 2/0 wire and 1.83 for 1/0 which seems really wierd. Guess I'm going with the 2/0 wire since its cheaper?? Not sure why the bigger stuff is cheaper unless it has to do with supply and demand. Hey Tom they just poured my floor today. I'm guessing they will put the steps to the second floor in on Monday.

You best figure out if the 2 pole breaker you plan to use in your main panel will accept 2/0 wire. My guess is it won't

 

[mrb]

You best figure out if the 2 pole breaker you plan to use in your main panel will accept 2/0 wire. My guess is it won't

it wont, but he can run copper from the main panel to a JB where he can use polaris connectors or something to transition to the aluminum

 

[triplethreat]

That was one of my worries that the 100 amp breaker wouldn't fit with the 2/0 AL wire. Will it fit with 1/0 wire? What are polaris connectors? Would it make since to use a junction box since the 2/0 wire is cheaper then the 1/0 wire?

 

[walrus]

That was one of my worries that the 100 amp breaker wouldn't fit with the 2/0 AL wire. Will it fit with 1/0 wire? What are polaris connectors? Would it make since to use a junction box since the 2/0 wire is cheaper then the 1/0 wire?

Some will take 1/0, best check before making that purchase. Polaris connectors are a insulated device with set screws that allow one to connect wires of different(or same) sizes together. Not sure about the copper to aluminum stuff. A large PVC box is pretty expensive so not sure on 1/0 or 2/0

 

[nadogail]

You might consider installing boards laying flat in the area under the roof and running the SE cable on the top of that. This will support the cable its entire length, not just in spots and will conceal the cable from view from the bottom. Air will circulate avoiding the need to be so concerned about heat build up.

In the past, I have tied cable runs to waterpipes (not Fire Sprinklers) to provide support and give a neat appearance. The inspector passed it without comment.