Compressor electrical needs?

[dipan]

I have a closet designed for compressor, but I'm the designer so ...

It has a dedicated 220v 30-amp outlet and based on hp I was working on the assumption that this would be enough for almost any 5hp 2-stage compressor. I called the vendor aircompressorsdirect.com and spoke to a product expert. He says I can at most run 3hp because of startup current. This doesn't seem to jive with what is said on this forum (I did search), so he suggested a Quincy 3.5hp unit Q13160VQ 60 gallons. This will probably be enough for me but I usually overdo my equipment purchases on purpose. I will probably in a year or two have a small blast cabinet as the biggest air hog.

I went with the Quincy but though it would be wise to ask this here to see what the real experts say. Initially I was looking at an Atlas Copco 2-stage 60 gallon compressor that was advertised as 5hp and as having an integrated after cooler. I thought that was great so I didn't have to worry as much about water in the lines. And I figure they know what they are doing as they own and make many of the other branded compressor lines out there including Quincy. It's the AR5EV, FWIW. He said that would definitely not work on a 30 amp breaker.

 

[CNGsaves]

GJ Sparkies will chime in soon . . .
. . . . .
. . . . . . .BUT . . . the gist you need to know:


HP . . . yep that is HORSEPOWER listed on the electric motor plate. Post up PIC of the motor plate and GJ Sparkies can give you exact details.

HP will determine the wire size and breaker size for compressor. Likely will need to be DIRECT WIRED for air compressor.

Finally . . . no such thing as 220v . . . . all wiring in USA is 240v !!

P.S. UPDATE GJ Profile with a Location as electrical codes differ by country.

 

[justsam]

Well, as usual, "it depends".

A 5HP motor, per NEC tables would require a 35Amp circuit. If your 30Amp circuit has been wired with #10 Romex, than it is rated at 30 Amps. If it has been wired with THHN, individual conductors, it is good for 35 Amps, and will support the 5HP.

Please note it is the wire, not the breaker that is the limitation. For motor applications the breaker can be beyond the normal 30Amp capacity for #10 wire.

You need to use a plug/receptacle rated for 3.5HP, most are good up to 3HP, lest it must be hardwired. If you can not see the breaker from the closet, there must also be some form of disconnect.

That looks like a great compressor by the way, and I wish mine were in a closet!

 

[teamo]

I would never let an existing circuit be the deciding factor as to which compressor I would purchase. You should buy the compressor that will suit your needs and if need be run a new circuit for it with the proper sized breaker.

 

[dipan]

GJ Sparkies will chime in soon . . .
. . . . .
. . . . . . .BUT . . . the gist you need to know:


HP . . . yep that is HORSEPOWER listed on the electric motor plate. Post up PIC of the motor plate and GJ Sparkies can give you exact details.

HP will determine the wire size and breaker size for compressor. Likely will need to be DIRECT WIRED for air compressor.

Finally . . . no such thing as 220v . . . . all wiring in USA is 240v !!

P.S. UPDATE GJ Profile with a Location as electrical codes differ by country.

I don't have the compressor yet to post the motor plate image. The wiring is done and cannot easily be redone. This is a finished garage so I am reluctant to tear out drywall to run a new line. The wire I do not recall as to gauge but I do know it is a single gray wire with aluminum conductors. Breaker and wire installed by licensed electrician and inspected. Sorry, 240v ... I always get confused between 220, 230, 240v. Profile updated!

 

[dipan]

Well, as usual, "it depends".

A 5HP motor, per NEC tables would require a 35Amp circuit. If your 30Amp circuit has been wired with #10 Romex, than it is rated at 30 Amps. If it has been wired with THHN, individual conductors, it is good for 35 Amps, and will support the 5HP.

Please note it is the wire, not the breaker that is the limitation. For motor applications the breaker can be beyond the normal 30Amp capacity for #10 wire.

You need to use a plug/receptacle rated for 3.5HP, most are good up to 3HP, lest it must be hardwired. If you can not see the breaker from the closet, there must also be some form of disconnect.

That looks like a great compressor by the way, and I wish mine were in a closet!

It was wired with an aluminum conductor wire, very thick but I don't know the gauge. My floor outlets were run with individual copper conductors, but there is no floor outlet in this closet. What is a 3.5hp receptacle? The plug in the closet is a NEMA 14-30:

I can see the breaker from the closet if the door is open, across the garage. Is that OK? I was planning on wiring a plug to the compressor using some Carol 10g wire, but I don't know what the compressor has until it gets here, 3 or 4 conductors.

 

[dipan]

I would never let an existing circuit be the deciding factor as to which compressor I would purchase. You should buy the compressor that will suit your needs and if need be run a new circuit for it with the proper sized breaker.

That is a valid argument. The Quincy 3.5hp is, best as I can figure, more than I need now (basic air tools now, soon spraying equipment for woodworking, and eventually metalworking tools including basic blast cab), and something I will probably grow right into capacity wise, but not having the experience, I typically overbuy on machine to ensure it will meet my needs in the future, but the electrical is preventing me from doing so right now. I am not going to rewire now for a possible future use, however. I should have considered needing more than 30 amps at the closet, but I made that mistake already.

 

[teamo]

I checked your link to those compressors. That Quincy 3.5 HP looks pretty nice. You'll want to pay close attention to the CFM rating and add up the air usage of tools that will be running simultaneously plus a little extra. There is lots of information on the internet for sizing your air needs. The other link that you provided was for a 3 phase compressor. Most likely you only have single phase in a residential service.

 

[dipan]

I checked your link to those compressors. That Quincy 3.5 HP looks pretty nice. You'll want to pay close attention to the CFM rating and add up the air usage of tools that will be running simultaneously plus a little extra. There is lots of information on the internet for sizing your air needs. The other link that you provided was for a 3 phase compressor. Most likely you only have single phase in a residential service.

For some reason they have 3-phase listed in specs but show 1-phase in the title for the product listing for the Atlas Copco. Somewhat confusing. I think it is actually 1-phase and they listed the specs wrong. I will try to do a better estimates with one of those tools. Thanks....

 

[dogdog]

Not an expert but this similar topic have been posted before ..... It have something to do with in-rush / motor start currents.... a 5HP calculate something recommended up sized to a 40AMP single phase 240v circuit.... think the exact detail you have to google those terms. something to do with FLA/FLC and in rush current...

Think that guy from aircompressordirect is also on this forum maybe he can clarify for you why.

the model in your link is a 3 phase one. there is another submodel that is 5HP and single phase.... maybe you just set the wrong link.


you can start from this link..

http://ecmweb.com/code-basics/motors-and-nec

 

[rburke65]

OMG.....did he say 220V ? Man your torches and get the pitch forks.....

 

[Pwrgeek]

This will probably get me roasted but if it were me I'd buy the 5hp and try it on the existing circuit. You're not going to burn anything up as long as you stick with the 30A breaker on 30A wire. If the motor is high quality and the compressor is a good one that starts unloaded you'll probably be fine. If it doesn't work then you need bigger wire but at least you haven't handicapped yourself in the future for something that might not be a problem.

I can tell you that my Quincy QT5 (very similar to the Atlas you linked) has been working just fine on my RV outlet in my garage (fed from 30A breaker) while I build out my shop.


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[wyliesdiesels]

Theres at least 2 new threads per week on here with this same scenario. A thread search would have revealed the answers to your situation.

I have a closet designed for compressor, but I'm the designer so ...

It has a dedicated 220v 30-amp outlet and based on hp I was working on the assumption that this would be enough for almost any 5hp 2-stage compressor. I called the vendor aircompressorsdirect.com and spoke to a product expert. He says I can at most run 3hp because of startup current. This doesn't seem to jive with what is said on this forum (I did search), so he suggested a Quincy 3.5hp unit Q13160VQ 60 gallons. This will probably be enough for me but I usually overdo my equipment purchases on purpose. I will probably in a year or two have a small blast cabinet as the biggest air hog.

I went with the Quincy but though it would be wise to ask this here to see what the real experts say. Initially I was looking at an Atlas Copco 2-stage 60 gallon compressor that was advertised as 5hp and as having an integrated after cooler. I thought that was great so I didn't have to worry as much about water in the lines. And I figure they know what they are doing as they own and make many of the other branded compressor lines out there including Quincy. It's the AR5EV, FWIW. He said that would definitely not work on a 30 amp breaker.

Heres the low down for wiring a motor circuit to be code compliant:

Wire is to be sized at 125% of NEC table FLC. For a 5HP motor, with an FLC of 28a, 35a wire is needed. This means #8/2 NM-b (#10/x NM-b is too small because NM-b is limited to the 60* c ampacity....

Breaker can be MAX 250% NEC table FLC....This is to compensate for motor starting in-rush current which can be 4x-8x FLC...The breaker is allowed to be rated for more than the wire ampacity because it is only for protecting agaianst short circuits and ground faults. Over current protection is provided by the overloads in the motor starter or integral overload in the motor.

A disconnect is required if farther than 50' from and not within sight of the breaker panel....

A plug and recpeticle CAN ONLY be used IF they are rated for at least the same HP as the motor. Standard NEMA recepticles and plugs are rated to about 3HP. An example of a plug and recepticle with a higher HP rating is pin and sleeve connectors. But theyre expensive...

It was wired with an aluminum conductor wire, very thick but I don't know the gauge. My floor outlets were run with individual copper conductors, but there is no floor outlet in this closet. What is a 3.5hp receptacle? The plug in the closet is a NEMA 14-30:

I can see the breaker from the closet if the door is open, across the garage. Is that OK? I was planning on wiring a plug to the compressor using some Carol 10g wire, but I don't know what the compressor has until it gets here, 3 or 4 conductors.

Need to know the gauge of wire especially with aluminum.

A NEMA 14-30 is the incorrect recepticle to use even if it was rated for the correct HP. The correct recepticle would be a NEMA 6-** outlet.

NEMA 14-** is a dual voltage grounded 4-wire outlet. A 240v motor doesnt need the 4th/neutral wire.

How far away is the breaker panel?

Cordage is not to be used for non-portable fixed in place equipment...

This will probably get me roasted but if it were me I'd buy the 5hp and try it on the existing circuit. You're not going to burn anything up as long as you stick with the 30A breaker on 30A wire. If the motor is high quality and the compressor is a good one that starts unloaded you'll probably be fine. If it doesn't work then you need bigger wire but at least you haven't handicapped yourself in the future for something that might not be a problem.

I can tell you that my Quincy QT5 (very similar to the Atlas you linked) has been working just fine on my RV outlet in my garage (fed from 30A breaker) while I build out my shop.

Sent from my iPhone using Tapatalk

Consider yourself roasted!!

Sure it may work. But its not code compliant.

 

[dipan]

Theres at least 2 new threads per week on here with this same scenario. A thread search would have revealed the answers to your situation.



Heres the low down for wiring a motor circuit to be code compliant:

Wire is to be sized at 125% of NEC table FLC. For a 5HP motor, with an FLC of 28a, 35a wire is needed. This means #8/2 NM-b (#10/x NM-b is too small because NM-b is limited to the 60* c ampacity....

Breaker can be MAX 250% NEC table FLC....This is to compensate for motor starting in-rush current which can be 4x-8x FLC...The breaker is allowed to be rated for more than the wire ampacity because it is only for protecting agaianst short circuits and ground faults. Over current protection is provided by the overloads in the motor starter or integral overload in the motor.

A disconnect is required if farther than 50' from and not within sight of the breaker panel....

A plug and recpeticle CAN ONLY be used IF they are rated for at least the same HP as the motor. Standard NEMA recepticles and plugs are rated to about 3HP. An example of a plug and recepticle with a higher HP rating is pin and sleeve connectors. But theyre expensive...



Need to know the gauge of wire especially with aluminum.

A NEMA 14-30 is the incorrect recepticle to use even if it was rated for the correct HP. The correct recepticle would be a NEMA 6-** outlet.

NEMA 14-** is a dual voltage grounded 4-wire outlet. A 240v motor doesnt need the 4th/neutral wire.

How far away is the breaker panel?

Cordage is not to be used for non-portable fixed in place equipment...



Consider yourself roasted!!

Sure it may work. But its not code compliant.

Lots of good information here. I appreciate your comments despite my poor use of the search tool. The breaker panel is about 30 feet away but the space in between is a finished space. There is some limited attic access however. Looks like my best bet for a 5hp compressor based on your description is rewire with #8 and change the breaker to 50 amps. I would have to consult an electrician for this as I like to avoid messing with high voltage panels. I will heed your recommendations for direct wiring the 3.5hp Quincy but will probably get an electrician for that as well.

As an aside, there is a dust collector (Oneida) for woodworking in another closet next to the compressor closet, certainly not portable and definitely fixed-in-place. It has a 3hp rating and came with a NEMA 6-20 plug.

 

[matt_i]

My free advice is if you changed wires, go with copper and send the aluminum to the scrapyard. Its ok, compliant, etc, but not really the material one wants in an electrical circuit.

 

[CompressorPros.com]

We use 1.78 x Full Load amps to figure breaker size, so reverse math would put you needing a motor with FLA rating of 17 or below.

 

[wyliesdiesels]

My free advice is if you changed wires, go with copper and send the aluminum to the scrapyard. Its ok, compliant, etc, but not really the material one wants in an electrical circuit.

And thats ignorant advice. The aluminum alloys used for electrical wire nowadays are a lot better than the dangerous alloys used 5 decades ago in the 60s...

http://www.southwire.com/commercial/ALBuildingWire30YrsOfReliability.htm

 

[justsam]

We use 1.78 x Full Load amps to figure breaker size, so reverse math would put you needing a motor with FLA rating of 17 or below.

Seems a bit backward to base it on breaker size. Breakers are easily changed, for moderate cost.

Assuming he wants to change to something larger, the issue is the existing wire size and type. In the 5HP case it must be capable of 35 Amps, which as discussed means 10ga thhn or 8ga Nm-b. If indeed aluminum, than yet larger wire will be required. Breaker could be determined from there.

Sounds like a nice compressor, so I would be tempted to hardwire it in and move on, unless there is serious need for more capacity.

 

[dipan]

I've been busy with work and finally got around to trying out the compressor. I plug in the compressor with 10g Carol cable and a NEMA 14-30 plug. The compressor runs but the motor overheats and trips its thermal protector. After a few minutes I am able to reset it. I'm trying to run it for an hour with the valves open to break it in per the manual, but the motor cuts out within minutes. Not sure what to do.

The compressor is in a closet but I have the door open and ambient temps are below 80F. The motor makes a cyclic humming noise before kicking into what sounds like a higher speed mode. When it's making this noise I can see a plate with springs within the back of the motor expanding and shrinking. Not sure what that's for either or if it's relevant.

 

[pattenp]

First thing a 5HP motor should not be on a cord and plug. Exactly what type cord is the Carol cable? Sounds like your motor is starving for power and is overheating.

 

[wyliesdiesels]

I've been busy with work and finally got around to trying out the compressor. I plug in the compressor with 10g Carol cable and a NEMA 14-30 plug. The compressor runs but the motor overheats and trips its thermal protector. After a few minutes I am able to reset it. I'm trying to run it for an hour with the valves open to break it in per the manual, but the motor cuts out within minutes. Not sure what to do.

The compressor is in a closet but I have the door open and ambient temps are below 80F. The motor makes a cyclic humming noise before kicking into what sounds like a higher speed mode. When it's making this noise I can see a plate with springs within the back of the motor expanding and shrinking. Not sure what that's for either or if it's relevant.

Do u have a clamp meter?

If u do, measure the current on both legs while the motor is running.

What is the voltage at the starter terminals while the motor is running?

The 14-30 plug is the wrong plug for 240v equipment and a 5HP motor should be hardwired as pattenp brought up above.

 

[md21722]

It sounds like there is something wrong with the compressor motor or the wiring. A clamp meter and/or volt meter may provide some insight, but I would start thinking about calling the vendor about a warranty. The plugs are not code compliant, but wouldn't cause the issue you're having.

 

[dipan]

Do u have a clamp meter?

If u do, measure the current on both legs while the motor is running.

What is the voltage at the starter terminals while the motor is running?

The 14-30 plug is the wrong plug for 240v equipment and a 5HP motor should be hardwired as pattenp brought up above.

Unfortunately no clamp meter, but I thought maybe a simple wiring error. Your prompt got me to pull out the voltmeter. 120VAC between hot legs. That sounds like it could be my problem. At the wall, I get 240VAC between the flat blades, but the instructions for the plug (Leviton) direct 3 wire configurations to use one flat blade and an angle blade for the two hot wires. Looks like the in-wall wiring is four wire, but I need to wire the plug for three wire, using both flat blades and the ground pin, leaving the angled blade disconnected? At the wall I measure 0 VAC between ground and the angled blade.

 

[dipan]

Yes, I realize the use of the plug is not code compliant but I have a few of these plugs around and thought I would make sure it works before hardwiring.

 

[wyliesdiesels]

Unfortunately no clamp meter, but I thought maybe a simple wiring error. Your prompt got me to pull out the voltmeter. 120VAC between hot legs. That sounds like it could be my problem. At the wall, I get 240VAC between the flat blades, but the instructions for the plug (Leviton) direct 3 wire configurations to use one flat blade and an angle blade for the two hot wires. Looks like the in-wall wiring is four wire, but I need to wire the plug for three wire, using both flat blades and the ground pin, leaving the angled blade disconnected? At the wall I measure 0 VAC between ground and the angled blade.

Sounds like the motor is getting 120v instead of 240v.

 

[warren57]

Verify what gauge your aluminum feed is. Normally aluminum feed is used on higher amp circuits to save cost of large gauge copper.
Now if you were wiring in from the start, a 30' run of copper is a small expense, so go to larger gage aluminum is no big savings. But you have aluminum in place, so see what you have, because the sparky sized it for a load. You may have wire already sized for the amps you want/need.
Many factors are used in sizing wire. Amps, temp., length of run, type of wire insulation, voltage drop, etc.
But a pretty accurate rule of thumb is... If using aluminum conductors, the wire gauge size is one size larger than copper. So 30 amps with a copper conductor is 10 gauge. In aluminum the same 30 amp circuit would take a 8 gauge conductor.
A 40 amp circuit with copper would use 8 gauge conductor, while a 40 amp circuit in aluminum would be a #6 conductor.
Check and see what size breaker your circuit is attached to. The wire has the gauge stamped in the insulation so you should be able to see what you have, then you could determine the max. Load that cable is rated for.
Next, if it needs up sizing, knowing the space is finished, it must be in a garage, so run a surface mounted conduit for new wire.



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[pattenp]

You got the plug wired wrong. On a 14-30P the two flat blades (X & Y) are the two hots (240V), the (W) "L" shaped blade is neutral and the (G) "U" shaped prong is ground. For the compressor you don't use the "L" neutral. The neutral provides 120V using either one of the hots.

 

[dipan]

Well the motor runs better at 240v than 120v. Go figure... Thanks guys

 

[dipan]

Breaking in now. Tip for anyone with this compressor... use these rubber isolation mounts from McMaster:

9376K26
Vibration Damping Sandwich Mount, Male/Male, 3/8"-16 Thread, 1-5/8" High, 2" Wide, Natural Rubber
http://www.mcmaster.com/#9376K26

And drill the floor for tapped 3/8" redheads with 1/2" masonry bit, using the inner margin of the slots for the center of the drill hole. I used the center for some leeway but the metal flange on the rubber mount is so big it only fits with the threaded post at the inner margin. I considered drilling but decided, even deformed, the mounts work just fine. Under $22 shipped as well.