Electric Requirements for a New Compressor

[Chasbec]

I'm getting ready to by a new 230 volt, single phase 5 HP compressor. The specs say it requires a 60 amp dual pole breaker. I'm pretty sure that's exactly what I'm looking at in my panel, but want confirmation from people who know for sure. Here's what I see: View media item 52442
Thanks in advance!

 

[acer66]

That is unfortunately a 230V 30A breaker not a 60A but are you sure the compressor needs 60A?
That sounds pretty high to me.

 

[Chasbec]

Geez, I really thought the twin 30 amp breaker was what I needed
Here are the specs:
The 80 Gallon 2-Stage Air Compressor is designed to provide continuous power and is built to last.
5 HP (as rated by engine manufacturer) 230V 2-stage air compressor
175 max. PSI and 80 gal. ASME tank
15.8 CFM @ 90 PSI
100% continuous duty all cast iron pump
230V single phase motor, no starter required
Includes finned intercooler
Mounted discharge valve
Extended design life lasts 15,000+ hrs.
One year industrial grade warranty on complete machine - Pump warranty extended to two years with use of Ingersoll Rand's All Season synthetic lubricant, included
Breaker: 60 A dual pole breaker
Wire Gauge: 10 ga. if less than 50 ft. from circuit breaker to the compressor; 8 ga. if 51 to 100 ft. from circuit breaker to compressor
Voltage: Minimum 225 V at pressure switch
Full Load Running Amps: 22.5 A
Must be hard-wired, no plugs allowed

 

[Chasbec]

Here's my entire garage panel. There are a pair of 30 amp dual poles one above the other, currently not being used. Can these be combined into a 60 amp dual pole?
View media item 52452

 

[sands35]

No, you can't do that.

From the IEC tables, a 50 amp breaker on 10 guage wire is required. Motor and breaker selection isn't the same as with other load devices though.

The standard FLA for a 5 hp motor is 28 amps. You can try a 30 amp breaker and see if that trips. If not, you are good to go. If it trips, you will need a 50.

Schnieder IEC excel Calculator

50 amp breakers are around $15 and the swap is pretty easy.

 

[pattenp]

You can't combined two 30A breakers to get 60A, it doesn't work that way. You need to buy a new 60A DP breaker and replace the existing 30A DP breaker. The start-up amps are high is why the instructions say 60A. As said above you may get by with less of an amp breaker. Also the #10 wire needs to be THHN wire not NM-b (Romex).

 

[Chasbec]

But what about the manufacturer's specs calling for 60 amp dual pole? Do you think that's a typo or something? I'd hate to drop some big money on this and find out my electrical service isn't up to the task...

 

[Chasbec]

You can't combined two 30A breakers to get 60A, it doesn't work that way. You need to buy a new 60A DP breaker and replace the existing 30A DP breaker. The start-up amps are high is why the instructions say 60A. As said above you may get by with less of an amp breaker. Also the #10 wire needs to be THHN wire not NM-b (Romex).

Thanks. Do you think it's a problem having a 60 amp circuit, along with all my other circuits if the entire box is only 100 amps?

 

[sands35]

No, it's not a typo.

The breaker is sized to not trip for startup amps. The wire is sized for running amps. The wire will pull more than it's rating at startup, but that is only for a 1/2 second or something so it's fine.

This is spelled out in the IEC calculations to select wire and breakers.

If the motor is well behaved and there is an unloader in the compressor, you may be OK at a 30 amp breaker. It won't hurt anything to use a breaker that is too small. It just won't run for very long.

 

[sberry]

Its a max breaker rating, you could probably put 2 of those on a 60A circuit.

 

[Mustang51js]

Your max amps is 22 so you can use 10 wire which is what you have on that breaker now, just swap it out to a 60 amp breaker,even though it seems high to me.

 

[Charles (in GA)]

It real simple, you go to Home Depot, Lowes, your hardware, whatever, and get a Siemens double pole 60 amp breaker (I feel sure a 40 or 50 would work, even the 30 might) and you swap it out, doesn't take a moment to swap it after the front cover is removed. My true 7½ hp two stage which draws about 32 amps, starts just fine on a 50 amp breaker, cannot imagine why yours would need more than a 40.

Charles

 

[bmxdad]

It real simple, you go to Home Depot, Lowes, your hardware, whatever, and get a Siemens double pole 60 amp breaker (I feel sure a 40 or 50 would work, even the 30 might) and you swap it out, doesn't take a moment to swap it after the front cover is removed. My true 7½ hp two stage which draws about 32 amps, starts just fine on a 50 amp breaker, cannot imagine why yours would need more than a 40.

Charles

You can't just swap a 30 amp breaker for a 60 amp and call it good. Wire needs to be sized ... or am I missing something?

Personally, I'd try it on the 30 amp and see how it goes ... a new circuit with the correct breaker and wire if it doesn't work.

 

[trentonmakes]

You can't just swap a 30 amp breaker for a 60 amp and call it good. Wire needs to be sized ... or am I missing something?

Personally, I'd try it on the 30 amp and see how it goes ... a new circuit with the correct breaker and wire if it doesn't work.

Looks like he's good as long as compressor is not more than 50feet from panel

Sent from my LG-D801 using Tapatalk

 

[Evan(CA)]

Also the #10 wire needs to be THHN wire not NM-b (Romex).

Not true.

 

[wyliesdiesels]

You can't just swap a 30 amp breaker for a 60 amp and call it good. Wire needs to be sized ... or am I missing something?

Personally, I'd try it on the 30 amp and see how it goes ... a new circuit with the correct breaker and wire if it doesn't work.

Wire for motor circuits is sized differently than standard branch circuits. Breakers can be rated higher than the wire ampacity because the breaker for a motor circuit only protects against short circuits and ground faults but not overloads. Overloads are handled by either the overload relays in the motor starter or the overload on the motor itself(red push button).

So its code acceptable to have a #10 THHN wire feeding a 5hp motor with a 60a breaker.

Other things to keep in mind:

If its farther than 50' from and not within sight of the panel then a disconnect is required.

Not true.

How so? 28a FLC x 125% = 35a. #10 NM-b is rated at 30a so the wire WOULD need to be THHN if #10....What pattenp said is correct!

 

[Evan(CA)]

How so? 28a FLC x 125% = 35a. #10 NM-b is rated at 30a so the wire WOULD need to be THHN if #10....What pattenp said is correct!

10/3 romex could absolutely be used in that situation as long as it's protected by a 30a breaker. NM is required by law to use 90 degree wire so the only difference between it and THHN is when it comes to sizing the breaker for over current protection.

 

[jloehlein]

I agree with others that 60 amps seems really high for a 5hp compressor. I have a 7.5hp compressor and it called for 31 amps running, we wired it up on a 40amp breaker and it's been fine. It is also right next to the panel, not sure that that matters.

 

[wyliesdiesels]

10/3 romex could absolutely be used in that situation as long as it's protected by a 30a breaker. NM is required by law to use 90 degree wire so the only difference between it and THHN is when it comes to sizing the breaker for over current protection.

However, u completely ignored the 125% rule for wire size for motor circuits.

And u cant use the 90* c ampacity. Its for derating purposes only.

So no #10 NM-b wouldnt be upto code for a 5HP motor.

And yes the 60a breaker seems overkill but thats what the manufacturer calls for and u would need to wire it PMI...

 

[Evan(CA)]

However, u completely ignored the 125% rule for wire size for motor circuits.

And u cant use the 90* c ampacity. Its for derating purposes only.

So no #10 NM-b wouldnt be upto code for a 5HP motor.

And yes the 60a breaker seems overkill but thats what the manufacturer calls for and u would need to wire it PMI...

You are using the standard 5hp 28a at 230v but the manufacturer's plate above states 22.5 FLA.

 

[wyliesdiesels]

Motors arent wired by nameplate amps. They are wired by NEC FLC table amps.

Sure u could wire it based on nameplate amps but thats not upto code...

 

[CNGsaves]

You are using the standard 5hp 28a at 230v but the manufacturer's plate above states 22.5 FLA.

Oh no . . . . here we go again !!

. . . . . . sound of munching on popcorn . . . . .

As GJ Sparkies have pointed out many times. electric motors with HP rating are wire-sized by the HP . . . and NOT by the amps on the motor tag.

 

[wyliesdiesels]

^^^No kidding!

 

[pattenp]

A little knowledge can be dangerous.

 

[Evan(CA)]

I'm looking for the specific code now but until then

http://www.electricianmath.com/neccalculations/motorconductors.htm

"Example. Say you have a 5 HP 240 volt single phase motor. What is the minimum allowable 60 degree conductor to supply this motor?
Well, from the flc table we find the flc to be 28 amps. Times 125% is 35 amps. Checking table 310.16 we see that a #8 AWG would be needed in the 60 degree column. A #10 has an ampacity of only 30 amps and would not be at least 35 so it is too small.
Note, here is a complication. The code allows that if the calculated value for a single motor conductor does not match a rating of an available conductor, then the next size smaller can be used. So for a single motor, a conductor can be selected which is the next size smaller. This is not true for feeders for more than more than one motor, as will be seen in the next example. So a #10 is alright, after all."

 

[pattenp]

One thing you are missing is Nm-b is sized at 60C whereas THHN is 75C, so #10 THHN is 35A.

 

[engineer031]

All you need is a 40 amp breaker and run #8 wire this is not a true 5 HP you have and since you have a double 30 amp in there you can try it, it may work for you and if it trips it then go get a 40 amp

 

[Dagny]

Don't forget the temperature rating of the terminals. The cummins guy knows his lectric.

 

[Chasbec]

Wow! I had no idea how complicated all this was. Anyway, the bottom line of my post is to find out if my garage electrical service can handle the requirements of this compressor (with new 60 amp breaker and possibly some upgraded wire). It's on sale and I have to move quickly but want to make sure it's not something I'll be trying to unload on Craigslist in two weeks.

I guess what I'm seeing in all these postings is that it will work, without a problem. Being completely ignorant of all stuff electrical, my only concern is that I won't lose my lights and other equipment when the compressor turns on. Kinda like overwhelming the panel (is that even a thing?).

Thanks,
Chuck

 

[sberry]

It only pulls 22A run, not 60, in reality it will run from a 10 wire and a 30 breaker. There are thousands of them in use every day wired that way. It isn't going to overload your service.

 

[pattenp]

Your lights may dim for a second when the compressor kicks on but that's it.

 

[Chasbec]

OK, thanks guys! Now I can make an informed decision.

 

[Evan(CA)]

One thing you are missing is Nm-b is sized at 60C whereas THHN is 75C, so #10 THHN is 35A.

So what is the point of their example? Is it only relevant to older panels with breakers only rated at 60c? However with that logic since a 35a conductor exists would they then require you to retro everything for use with that if you didn't want to upsize the 60c wire? I'd like to see the exact wording of the exemption because it sounds like it was written for this exact situation.

 

[sberry]

There are a 1000 ways to burn the shack down. Whatcha think the odds of him doing it are cause he used a 10 cable with a 30 on one of these units are?
I wired a few wrong when I was a kid, the ones with bigger motors,,, people dead, compressor still works.

 

[AndyCBR]

Oh no . . . . here we go again !!

. . . . . . sound of munching on popcorn . . . . .

As GJ Sparkies have pointed out many times. electric motors with HP rating are wire-sized by the HP . . . and NOT by the amps on the motor tag.

What about motors with rating "SPL"?

 

[LS6 Tommy]

Not true.

Can't use NMB as a cord or "whip".

Tommy

 

[94EG8]

I'm not saying it's right but I've had no issues with my 5hp (23A) compressor on a 30A breaker and #10 wire.

 

[Evan(CA)]

There are a 1000 ways to burn the shack down. Whatcha think the odds of him doing it are cause he used a 10 cable with a 30 on one of these units are?
I wired a few wrong when I was a kid, the ones with bigger motors,,, people dead, compressor still works.

0. I am not a motor expert obviously but it seems to me that the 125% increase in wire size is just a safety precaution to account for voltage drop since the wires are normally overfused for the start up load.

 

[Evan(CA)]

Can't use NMB as a cord or "whip".

Tommy

Who said anything about that? We're talking about feeding the box/dc with nm and from there you'd use flex or seal tight to the compressor.

 

[pattenp]

So what is the point of their example? Is it only relevant to older panels with breakers only rated at 60c? However with that logic since a 35a conductor exists would they then require you to retro everything for use with that if you didn't want to upsize the 60c wire? I'd like to see the exact wording of the exemption because it sounds like it was written for this exact situation.

There is no NEC allowance to use the next smaller size conductor for the motor supply conductors if the calculated amp size is not listed in the tables as is the case for 60C temp for #10 which is 30A, not 35A. Based on needing 35A you will need to use either #8 NM-b at 40A(60C) or #10 THHN at 35A(75C). If the devices in the panel are rated only at 60C then you use #8 at 60C.