I am installing a 125 amp panel in my garage. We have 360 amp service to the meter, split into two, 200 amp on for the house and the other for the garage.

My question is what qauge/type cable do I need from my split panel to the 125 amp panel that is 75 feet away.

  • Will there be a breaker at the meter protecting the cable from carryng more than 125A? If so you may want to consider a panel rated for more than 125A, as getting plenty of spaces in your panel is a very important thing to do right now. You won't have another chance to do that cheaply. – Harper - Reinstate Monica Aug 30 '18 at 14:04
  • Yes there will be a breaker at the meter. I appreciate the thought of a higher rated panel but was hard to pass up a free panel with all the breakers included, lol. – tom provines Aug 30 '18 at 15:15
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    What make/model is the panel you are putting in? Also, is this run indoor, overhead, or underground? – ThreePhaseEel Aug 30 '18 at 23:46

Table 310.15(B)(16) from the 2017 NEC provides the information you need:

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Assuming a 75 degree temperature rating, you could get away with 1 AWG copper or 2/0 AWG aluminum or copper clad-aluminum.

  • Thanks, that helps. Planning on burying so think temp won't be an issue – tom provines Aug 30 '18 at 15:16
  • Just to clarify, the chart indicates the temp rating of each conductor type, not ambient temperature - it assumes an ambient temperature of 30 C. For example, TW copper wire is rated to 60 C, and THHW is rated to 75 C (wires heat up as current flows through them). There are additional considerations for temperature rating if you'll be running multiple conductors in the same conduit, but the above chart is sufficient for a single run. So, to simplify it, you can just look at the individual conductor type in the chart that you plan to buy to ensure that you get the right gauge. – Nick Anderson Aug 30 '18 at 16:16
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    Thhn is rated for 90 degree but the panels are usually 75 degree so you would be limited to the capacity of the temp of the breakers for actual capacity. – Ed Beal Aug 30 '18 at 18:30

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