230V Air Compressor Wiring

[CastleSeven]

Hoping you guys can spot check something for me.

I got a new Ingersoll Rand SS4L5 230V Standalone Air Compressor. It's got a single phase 5HP motor on it. Here's the nameplate:

https://imgur.com/a/9lEfhKk.jpg


The compressor is located ~40' from the breaker box through walls and ceiling. I'm no NEC expert, but I've been reading through various sections and have come up with the following gameplan:

NEC 430.6 says to use the appropriate table to determine the ampacity of conductors instead of the current rating on the nameplate. Table 430.248 indicates a 5HP motor at 230V has a full load of 28A.

NEC 430.22 says conductors supplying a single motor used in a continuous duty application should have an ampacity not less than 125% of the value determined by 430.6. So in this case, my conductors need to be capable of carrying 28A * 125% = 35A. So it looks like some 8/2 w/g Romex would do the trick here, as that's rated for 40A.

Now, for over current protection. According to NEC 430.32A and C, you can go either 125% OR up to 140% if 125% is too low to get the motor started. Rounding up it looks like a 40A breaker would do the trick for both cases and it matches the conductor rating.

I had planned to run the conductors to the wall behind the compressor, connect to an AC Disconnect (60A), and then use an 8/2 whip to connect from the disconnect to the compressor itself.


Have I forgotten anything? Does my approach seem like it'll work well based of what you guys have witnessed in your own shops?

 

[sberry]

Sounds like you got a grip on it. Carry on.

 

[exranger06]

You're correct on sizing the conductors and breaker. I just have 2 comments:
1. The flexible whip to the compressor only needs to have #10 wire. THHN wire has a different temperature rating than Romex, and #10 THHN can handle 35 amps. You can use the #8 whip if you want; it's just a little overkill.

2. Make sure the disconnect is rated for at least 5 HP. I didn't see any HP rating on the one you linked. Perhaps it is rated for at least 5 HP and Home Depot just didn't mention it on their site. Double check before buying. I used this disconnect on my compressor: https://www.homedepot.com/p/GE-60-Amp-240-Volt-Non-Fuse-Metallic-AC-Disconnect-TFN60RCP/100674085 It's super cheap and rated for up to 10 HP.

 

[Bert_]

Normal breakers can be 250% of fla.

40A breaker will be fine though. I might prefer a 50A just because it's the same price but a 40 is unlikely to ever be a problem.

 

[wyliesdiesels]

Hoping you guys can spot check something for me.

I got a new Ingersoll Rand SS4L5 230V Standalone Air Compressor. It's got a single phase 5HP motor on it. Here's the nameplate:

https://imgur.com/a/9lEfhKk.jpg


The compressor is located ~40' from the breaker box through walls and ceiling. I'm no NEC expert, but I've been reading through various sections and have come up with the following gameplan:

NEC 430.6 says to use the appropriate table to determine the ampacity of conductors instead of the current rating on the nameplate. Table 430.248 indicates a 5HP motor at 230V has a full load of 28A.

NEC 430.22 says conductors supplying a single motor used in a continuous duty application should have an ampacity not less than 125% of the value determined by 430.6. So in this case, my conductors need to be capable of carrying 28A * 125% = 35A. So it looks like some 8/2 w/g Romex would do the trick here, as that's rated for 40A.

Now, for over current protection. According to NEC 430.32A and C, you can go either 125% OR up to 140% if 125% is too low to get the motor started. Rounding up it looks like a 40A breaker would do the trick for both cases and it matches the conductor rating.

I had planned to run the conductors to the wall behind the compressor, connect to an AC Disconnect (60A), and then use an 8/2 whip to connect from the disconnect to the compressor itself.


Have I forgotten anything? Does my approach seem like it'll work well based of what you guys have witnessed in your own shops?

youre doing better than the majority of people who come on here AFTER theyve bought all the wrong wire and hardware.

good job on the research before you bought anything...

 

[sberry]

My neighbor asked, I told him 10, he got 8 and had a time connecting it.

 

[CastleSeven]

Thanks everyone for the help! I was grabbing my keys to get to the HW store when my electrician *finally* got back in touch with me. I had him come out, let him know what I had planned on doing, and he suggested that I would be fine with a 30A breaker and #10 wire. I was hesitant but who am I to tell an expert he's wrong? They got it all buttoned up (didn't have to use a disconnect since it's in direct sight of the breaker box), and it doesn't seem to have any issues starting.

 

[Bert_]

#10 thhn is fine. #10 Romex is technically to small but there are a ton wired that way that won't be a problem. No modern 5hp motor pulls 28A

A 30A breaker is to small though in my opinion. A 40 or 50 would be ideal. I will never understand why people undersize the breaker when the right one is the same price...

 

[wyliesdiesels]

#10 thhn is fine. #10 Romex is technically to small but there are a ton wired that way that won't be a problem. No modern 5hp motor pulls 28A

A 30A breaker is to small though in my opinion. A 40 or 50 would be ideal. I will never understand why people undersize the breaker when the right one is the same price...

because theyre stuck on 240.4(D), cant see past that and the values in 310.15(B)(16) [which is now back to 310.16 in the latest code; smh]. 'The breaker is sized by the wire size' ignorance.......

 

[vtjon]

because theyre stuck on 240.4(D), cant see past that and the values in 310.15(B)(16) [which is now back to 310.16 in the latest code; smh]. 'The breaker is sized by the wire size' ignorance.......

So I'm guilty of the breaker sized by the wire shortcut. Can you explain or tell me the section of the code where/how the breaker can be bigger?

Sent from my Pixel 3a XL using Tapatalk

 

[wyliesdiesels]

So I'm guilty of the breaker sized by the wire shortcut. Can you explain or tell me the section of the code where/how the breaker can be bigger?

Sent from my Pixel 3a XL using Tapatalk

240.4(G) and the table, references the specific code articles that give you info on that.

for motor circuits, see article 430, specifically table 430.52, which lists 250% of FLC for max size on the breaker.

 

[cosmopedro]

So it looks like some 8/2 w/g Romex would do the trick here, as that's rated for 40A.

So, I apologize for sounding dense, but by Romex are you referring to NM cable or flexible metal? Or something entirely different?

 

[Norcal]

So, I apologize for sounding dense, but by Romex are you referring to NM cable or flexible metal? Or something entirely different?

Romex® is a trademarked name for NM sheathed cable.

 

[cosmopedro]

Romex® is a trademarked name for NM sheathed cable.

I know… that’s why I asked. There are old-school folks around here who use it interchangeably to mean NM and/or MC (don’t know why) hence the question.
I’m fixing to do almost exactly the same thing with a used Champion VR5-8 w/an R15-A pump and Baldor single phase 5HP motor and didn’t want to buy bigger wire than necessary… mine came to me wired w/a 60A starter and 6 gauge wire and I didn’t want to run 75’ of 6 gauge if I didn’t need to.

do y’all think I could manage with 10 gauge over that (75’) distance, or should I run 8 - or stick with 6?

 

[alfredeneuman]

do y’all think I could manage with 10 gauge over that (75’) distance, or should I run 8 - or stick with 6?

#10 in conduit or MC cable should be fine.
Remember, the actual load is far less than the NEC table's

 

[cosmopedro]

#10 in conduit or MC cable should be fine.
Remember, the actual load is far less than the NEC table's

And I guess the ‘proof in the pudding’ is whether I get nuisance tripping or not, right?!? Is there any other negative to expect from using #10?

 

[alfredeneuman]

Is there any other negative to expect from using #10?

At 3.6% voltage drop it's beyond the suggested limit for general circuits (3%) but well within the limit for motors (a nonissue) That's the only thing I can think of.

 

[wyliesdiesels]

At 3.6% voltage drop it's beyond the suggested limit for general circuits (3%) but well within the limit for motors (a nonissue) That's the only thing I can think of.

suggested VD for circuits is 5%. 3% is for feeders

 

[Terry D]

suggested VD for circuits is 5%. 3% is for feeders

The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3%

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