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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: enter image description here

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!

  • See NEC 240.4 before you attempt to use anything larger than 30A ocp on #10 awg. – NoSparksPlease Oct 22 at 6:01
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    What do the installation instructions say about wiring it up? Those are what you should be following. – JACK Oct 22 at 12:41
  • @JACK, unfortunately the installation instructions say "consult an electrician". COVID is making it hard for me to get someone out here reliably, and I need this thing up and running safely. – CastleSeven Oct 22 at 12:59
  • @NoSparksPlease, thanks for the reference, looking at the code (instead of the linked article), NEC 440 seems to reference HVACR equipment in particular, so the 175% / 225% portion of my post may be irrelevant. – CastleSeven Oct 22 at 13:08
  • To avoid burning your garage down, respect breaker to wire size minimums. Or exceed the wire size, which will make it simpler if you find you need to increase the breaker size to avoid startup trips (hot take on that - pay no attention to starting it empty. If it's going to trip, it's most likely to trip when starting to refill after drawdown in use, unless it has a good unloader system to take the pressure off until the motor is wound up.) – Ecnerwal Oct 22 at 15:09
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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.

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  • How did you get 32.2 amps out of Table 430.248? That number is in the table for a 5HP motor, but it's in the 200V column (two hundred volts). The 230V column is at the far right (28A). – Harper - Reinstate Monica Oct 22 at 16:13
  • @Harper-ReinstateMonica, oops, thanks, will fix. – NoSparksPlease Oct 22 at 16:26
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I just so happened to have my electrician come out the day after I posed this question. For those wondering, I was fully comfortable with @NoSparksPlease answer, and was expecting them to go with a 40A breaker and #8AWG wire. However, after looking at the motor specs the electrician suggested 30A and #10AWG wire. He said they had wired several this way and never had seen anyone have issues getting them started. Everything appears to work fine!

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