Subpanel feeder ampacity

[Guest]

I posted this in the NEC section and got no replies. I noticed this was the better place to post this question:

>>>>I am going to hang a 200-amp meter/main combo on the outside corner of my garage at the front of the house. On the back wall of my garage there is a 12/24 125-amp subpanel with lugs. Additionally, I cut in another 12/24 125-amp subpanel in my 3rd bedroom behind the door.

QUESTION: What size feeder should I use to the subs? I either want to go 90-amp, 100-amp, or all the way to 125-amp depending on what is the most cost effective. Should I go aluminum or copper? If so, what size wire do I need. I'll go with x/3 w/ground Romex. Panel #1 is about a 35' run and panel #2 is about a 70' run. THANKS!
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Sorry for the double post! I'm a newbie here!

 

[hillbilly]

Re: Subpanel feeder ampacity

You'll need #4 THHN copper minimum for a 100A feed, #2 THHN copper minimum for a 125A. You wont find either size in "Romex". You will probably Have to run conduit and pull in single conductors (4 total in 1 conduit) to each panel. Your grounding (green) conductor and grounded (white) conductor can be smaller, check the code.

 

[iwire]

Re: Subpanel feeder ampacity

4 AWG THHN is only good for 100 amps if you have 90C terminations on each end, which you will not, or if you can use table 310.15 but that is not for subpanels.

Using table 310.16 you will need 3 AWG copper or 1 AWG Aluminum for 100 amps, 2 AWG copper or 1/0 aluminum for 125 amps.

As Hillbilly said NM (romex) is hard to come by in these sizes, however SER (service entrance cable) is available and this is what I would use.

Aluminum or copper each has advantages and disadvantages.

SER is more available in aluminum and we use it all the time.

 

[Guest]

Re: Subpanel feeder ampacity

Thank you for your replies. This is for my dwelling. I'm used to seeing SER then. I'd like to go with cable vs. pipe. I don't have access to any tables today. Can you post a table here or a link to a table? Here are the SER's I'm interested in at this point:

Option 1: SER Aluminum 100 amp.
Option 2: SER Copper 100 amp.
Option 3: SER Aluminum 125 amp.
Option 4. SER Copper 100 amp.

Or, just post the wire gauge for each option. Many thanks!