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What's up with HPWC?

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How big are you trying to go? 2 awg is rated for up to 130 amps

Kinda-sorta.

The insulation is rated to 130A for the heat of the conductor itself.

However, terminations on most residential equipment nowadays are 75 degC rating, so #2 is really only good to 115A where it attaches to the breakers and the terminals on the HPWC.

But if - as AWDtsla is doing - you're wanting to use a cable assembly (NM cable or SER cable) - you generally have to use the 60 degC column (95A). This is because NM cable (Romex) is always treated at 60 degC (except for derating factors), and SER cable must be treated at 60 degC if at any point it passes within or through thermal insulation.

Basically, the formula goes something like this:
  • Take conductor rating from 90 degC column (for new conductors only) and adjust for any derating factors (ambient temperature, number of current-carrying conductors in conduit, etc.) and write it down on line 1.
  • Take conductor rating from 75 degC column and write it down on line 2.
  • If using SER cable that will pass through or within insulation, or NM cable in any environment, take conductor rating from 60 degC column and write it down on line 3.
Then:
  • Take the smallest of these 3 numbers and write it on line 4 -- this is your maximum circuit rating and the maximum load you may apply on the circuit.
  • If a standard breaker size matches line 4, repeat that number on line 5. Otherwise round up to the next standard breaker size and write that on line 5. This is the maximum breaker size you may install.
  • If line 5 is greater than line 4, note that you MAY NOT apply a load greater than that of line 4, even if the breaker is larger. This is why 2/3 Romex (95A from 60 degC column) is not able to serve an 80A charging load, which requires a full 100A circuit rating.