I just got an Ingersoll Rand SS4L5 230V Standalone Air Compressor, and I need some spot-checking on my wiring configuration from my panel. First let's get the details out of the way:
I'm not sure from the image what the starting amps required are, but it looks like running amps are ~21.1A.
The install location is roughly 40' from the breaker through the walls/ceiling. Current thought is:
Conductors sized at 125% motor load current, which would be ~27A, so rounding to 30A would give me 10/2 w/g CU NM-B Romex. I've anecdotally seen people using 8ga here, so I'm not sure if that is overzealous on safety or not…
As for the breaker, this article references NEC 440.22, saying that 225% is an OK rating to target to get over the starting current required. I have absolutely zero idea if this is too much, or if I need to bump down to 175%.
225% would give me ~47A, and 175% would give me ~37A, so the difference between a 40A and a 50A breaker.
I've seen forums recommend 10ga romex and 60A breakers, 8ga Romex on 40A, 10's on a 40A (and when that failed he ran 6ga on a 60A)….
I just want to avoid tripping breakers on startup and burning my garage down…
Thanks for the help!
Best Answer
You are in the wrong section, 440 is refer equipment, you need too roll back to section 430, Motors, Motor circuits, and Controllers.
Part III Motor and Branch circuit protection
Then look at label: Continuous duty motor, Section 430.32.
More than 1 HP, Paragraph (A).
Thermally Protected, (2) A thermal protector integral with the motor, check, now we're looking at the right section: under 9A, shall not exceed 170%.
Table 430.248 FLA 1Ø AC, 5 hp, 28A, times 1.7, shall not exceed 47.6, so 45A from table 240.6(A). This is maximum, a 40A breaker would likely work fine and be acceptable by code.
Wire size, minimum 125% of 21.1 is 26.4, table 310.15 or 310.16 depending on year of code book, shows #10 wire, but with a **. So 240.4 says overcurrent protection for #10 conductors after any corrections can't exceed 30A, so you got to upsize to #8 AWG.