Confused About SEC Cable Size

[lostcause]

as i posted earlier, i used 1/0 aluminum for a 100a panel, and that was increased a size due to the length of the run. i know that in my panel, i could not have fit anything larger into the lugs, as it appears you can't. wherever you purchased the wire may be able to tell you what size is required (most electrical supply houses tend to have charts to cover that).

if you do a simple internet search, the results seem to show that #4 copper is an acceptable size for a 100a service entrance. i believe that #2 would be the correct size for aluminum wire. you're several sizes larger than that. if you have 2/0 copper, i believe that can actually carry a 200a service. again, mine are fairly educated guesses, as i am not an electrician, and i didn't even stay at a holiday inn express.

wire sizes from smaller capacity to larger as follows:

14
12
10
8
6
4
2
1
1/0 (0)
2/0 (00)
3/0 (000)
4/0 (0000)

 

[paccorti]

I think this explains what some of you were trying to tell me about SEC size.

According to this I could do a 4, 2, 1 or 1/0. Instead of a 1/0 maybe I'll do a 1 (THWN). It looks like the cable I have is rated for 200amps which way bigger than my panel.

Maybe that's what the panel really means a #4 cable to a 1/0 (on the panel it says 4 - 1/0)

Thanks for the help!

Peter

 

[paccorti]

Thanks lostcause your points make sense to me.

Peter

 

[_RaT_]

as i posted earlier, i used 1/0 aluminum for a 100a panel, and that was increased a size due to the length of the run. i know that in my panel, i could not have fit anything larger into the lugs, as it appears you can't. wherever you purchased the wire may be able to tell you what size is required (most electrical supply houses tend to have charts to cover that).

if you do a simple internet search, the results seem to show that #4 copper is an acceptable size for a 100a service entrance. i believe that #2 would be the correct size for aluminum wire. you're several sizes larger than that. if you have 2/0 copper, i believe that can actually carry a 200a service. again, mine are fairly educated guesses, as i am not an electrician, and i didn't even stay at a holiday inn express.

wire sizes from smaller capacity to larger as follows:

14
12
10
8
6
4
2
1
1/0 (0)
2/0 (00)
3/0 (000)
4/0 (0000)

and then it goes to MCM. I have a chunk of 1000 MCM at home that I pulled out of a job. I think 2000 MCM is the largerst but have never seen any.

 

[jenkinsph]

I think this explains what some of you were trying to tell me about SEC size.

According to this I could do a 4, 2, 1 or 1/0. Instead of a 1/0 maybe I'll do a 1 (THWN). It looks like the cable I have is rated for 200amps which way bigger than my panel.

Maybe that's what the panel really means a #4 cable to a 1/0 (on the panel it says 4 - 1/0)

Thanks for the help!

Peter

You can use #4 for a short run as you describe, and yes that is what the panel means, #4 thru 1/0 will fit the lugs.

 

[jenkinsph]

and then it goes to MCM. I have a chunk of 1000 MCM at home that I pulled out of a job. I think 2000 MCM is the largerst but have never seen any.

RaT,
I have often used 500 and 750 mcm wire on some Govt projects and prefer to paralell the wires rather than going larger than that. I would think 1000 or 2000mcm would be tough to work with. What are you going to use the 1000mcm for?

 

[eepete]

You should use a #2 for a 100 amp panel. But there is an exception in the NEC for residential use that lets you use a #4. These are copper conductors, I don't know what they bump up to for Al. So this is the smallest you can use.

You then need to figure out the resistance of the wire for the entire circuit with the conductor you're using and the length of the run. Then you use knowledge of your load to make sure there isn't too much voltage drop for your particular application. Remember that you have drop both to and from the panel. As already stated you need 4 wires which is what you said you had. The code also allows for a smaller ground, you'd have to look that up, ask here for an electrician, or consult an electrician.

I just put in a 100 amp sub panel, the run was 165' long, used #2 copper, and the drop at 100 amps is around 5 volts (if I remember correctly). The wire size was also influenced by bizarre pricing at a box store where #2 was cheaper than #4. This is also why I made the ground a #2 also.

So code dictates minium size, and the voltage drop might bump that up a size or two.

Pete

 

[_RaT_]

RaT,
I have often used 500 and 750 mcm wire on some Govt projects and prefer to paralell the wires rather than going larger than that. I would think 1000 or 2000mcm would be tough to work with. What are you going to use the 1000mcm for?

We pulled the 1000 MCM Cu out of a job and ran triple parallel runs of 750 MCM Al. The conduits were there and it made getting to the required current capacity simple.

 

[paccorti]

Thanks everyone. I think I'll get either the 1/0 or the #1 SEC in copper. That seems well above code (and is the max or close to the max this panel can take anyway). The #2/0 was $8/foot so at least it will be cheaper!

BTW is there any convention for putting the red hot and black hot into the main breakers (for example put the red left and black right or something like that)? Given the interleaved arrangement of the hot buses to breakers I wouldn't think it would matter.

Peter

 

[_RaT_]

Thanks everyone. I think I'll get either the 1/0 or the #1 SEC in copper. That seems well above code (and is the max or close to the max this panel can take anyway). The #2/0 was $8/foot so at least it will be cheaper!

BTW is there any convention for putting the red hot and black hot into the main breakers (for example put the red left and black right or something like that)? Given the interleaved arrangement of the hot buses to breakers I wouldn't think it would matter.

Peter

It does not matter. Often times you just have two blacks so there really is no polarity issue. When using aluminum, be sure to come back the next day and re-torque the lugs.