Hardwiring 80g/5hp compressor

[PT Doc]

Finally getting around to wiring up my compressor. The current outlet location has a 14-50 receptacle. That will be coming out and the choice then is either Liquidtite or flexible metal conduit. I'm leaning forwards the Liquidtite. I use fmc in the past and it's awkward to work with in regards to cutting.

I am adding a Leviton 60 amp switch in a Leviton box on the front of the unit in the location where mag starters generally go. So starting at the wall, I will need a 2 gang cover plater with hole, 90 degree liquidtite elbow, liquidtite conduit, straight liquidtite connector. From this Leviton box, I need a straight connector, liquidtite conduit and then a 90 degree elbow into the back of the starter/pressure switch on the side of the compressors. I will likely run 4 wires from the wall into the 60a switch box in case I want to pull 120v power for a fan for the compressor at a later time. Total wire length is less than 12 feet.

I have a Quincy qt5 without the mag starter. The fla on the Baldor is 23a I believe.

http://www.aircompressorsdirect.com/Quincy-251CP80VCB-Air-Compressor/p856.html

Any suggestions on size of liquidtite conduit? 10 THHN qty 4 wire size? Any other thoughts?

Thanks for the help.

 

[wyliesdiesels]

Do u have 3 phase 480v?

NEMA 16-50 is 3 phase 480v 50a.

 

[-Brent-]

Do u have 3 phase 480v?

NEMA 16-50 is 3 phase 480v 50a.

It's got to be a typo, I'm thinking. He probably meant 6-50.

 

[wyliesdiesels]

Well regardless of the possible typo, OP needs to list HP rating.

Sounds like its 5HP- if it is then OP needs #10 THWN or 8/2 NM-b

An inline fuse would be needed if a fan is gonna be used.

The switch will need to be rated for at least the same HP rating as the motor.

Does the pressure switch not have a switch?

 

[PT Doc]

Do u have 3 phase 480v?

NEMA 16-50 is 3 phase 480v 50a.

Sorry. Plug is 14-50. This is single phase 50a.

 

[PT Doc]

Switch: (10hp @240v)

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=MS602-FW&section=40132&minisite=10251

Switch enclosure:

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=N36NC&section=40153&minisite=10251
.

The Quincy compressor has a 5hp Baldor motor.

http://www.aircompressorsdirect.com/Quincy-251CP80VCB-Air-Compressor/p856.html

Thanks

 

[PT Doc]

Well regardless of the possible typo, OP needs to list HP rating.

Sounds like its 5HP- if it is then OP needs #10 THWN or 8/2 NM-b

An inline fuse would be needed if a fan is gonna be used.

The switch will need to be rated for at least the same HP rating as the motor.

Does the pressure switch not have a switch?

The fan is not happening anytime soon or maybe never. Since I have 4 wires I will pull the 4th to the Leviton switch enclosure just in case.

The factory pressure switch has a switch. I just want another way to shut the power off just in case since the main panel is on the side of the house.

Thanks for the help.

 

[PT Doc]

THHN is not appropriate in this application that will be in Liquidtite conduit? THWN needs to be used?

THHN specs:

*Multi-purpose building wire used in conduit and cable trays for service, feeders and branch circuits in commercial and industrial applications
*Can be used in wet or dry locations
*Insulation is high heat-and moisture-resistant PVC
*Jacket is abrasion-, moisture-, gasoline-and oil-resistant nylon
*Conductors are annealed (soft) copper

4 strands of #10 is ok in 1/2" liquidtite?

 

[Norcal]

THHN is not appropriate in this application that will be in Liquidtite conduit? THWN needs to be used?

THHN specs:

*Multi-purpose building wire used in conduit and cable trays for service, feeders and branch circuits in commercial and industrial applications
*Can be used in wet or dry locations
*Insulation is high heat-and moisture-resistant PVC
*Jacket is abrasion-, moisture-, gasoline-and oil-resistant nylon
*Conductors are annealed (soft) copper

4 strands of #10 is ok in 1/2" liquidtite?

I did not notice if the OP is installing outdoors, if not then THHN will be fine, but most is dual rated THHN, THWN.

 

[wyliesdiesels]

THHN is not appropriate in this application that will be in Liquidtite conduit? THWN needs to be used?

THHN specs:

*Multi-purpose building wire used in conduit and cable trays for service, feeders and branch circuits in commercial and industrial applications
*Can be used in wet or dry locations
*Insulation is high heat-and moisture-resistant PVC
*Jacket is abrasion-, moisture-, gasoline-and oil-resistant nylon
*Conductors are annealed (soft) copper

4 strands of #10 is ok in 1/2" liquidtite?

U can use THHN. Most THHN is dual rated THWN so its just habit to type THWN.

And since panel is out of sight u need the disconnect.

 

[PT Doc]

I did not notice if the OP is installing outdoors, if not then THHN will be fine, but most is dual rated THHN, THWN.

Yes, the compressor is being installed in an attached garage that will serve as my shop area.

Thanks for the help.

 

[PT Doc]

U can use THHN. Most THHN is dual rated THWN so its just habit to type THWN.

And since panel is out of sight u need the disconnect.

Thanks.

Any issues with number of wires in liquidtite? I have 1/2" and 3/4" that can be used. There will be 4 wires. I think I have #8 already so I will likely be using that.

Theoretically, could I use 4 of the same color (red) wires and tape the ends white, black, white?

 

[wyliesdiesels]

Thanks.

Any issues with number of wires in liquidtite? I have 1/2" and 3/4" that can be used. There will be 4 wires. I think I have #8 already so I will likely be using that.

Theoretically, could I use 4 of the same color (red) wires and tape the ends white, black, white?

U will need to use 3/4" if going with #8 but the EGC doesnt need to be #8.

I would just use 4 #10s.

It is not code compliant to phase tape wire that is #6 and smaller.

 

[zmaxmotorsports]

Id surface mount a deep 4sq or 4 11/16 box and bring a 90 degree seal tight or gf connector out the side of it instead of punching a hole in a blank cover.
That would make it easier to access things for installation/maintenance purposes anyway.

 

[PT Doc]

Id surface mount a deep 4sq or 4 11/16 box and bring a 90 degree seal tight or gf connector out the side of it instead of punching a hole in a blank cover.
That would make it easier to access things for installation/maintenance purposes anyway.

I would have done that but there is a double gang box that is already mounted flush with the drywall that has the 14-50 receptacle. Also, drywall is textured and painted so I would rather keep it all as is. Putting a hole in a double gang cover plate is easy and there might be a plate that has proper size hole already for this type of application. Will likely go with a stainless cover plate instead of the plastic.

Thanks

 

[PT Doc]

I'm finally getting around to wiring this up. This outlet is in my attached garage.

I will be using 1/2" liquidtite and will pull 4 10 g wires. I am pulling a neutral wire for possible future 120v fan. Currently, there is a 14-50 receptacle in a 2 gang box that is mounted in the wall. Garage is drywalled, textured and painted. I will use 90 degree elbow from this box then run the liquidtite flexible nonmetallic conduit to a leviton motor switch enclosure on the compressor that has a motor rated switch. Switch is rated for 60 amp @ 240v. From this switch enclosure, I will run liquidtite conduit to back of pressure switch.

This circuit is run directly from the side of house to the garage with 6g wire through the unfinished basement ceiling. Will I need to change the breaker out since I'll be finishing the compressors side with 10g wire?

Thanks again.

 

[wyliesdiesels]

To refresh my memory, these 4 #10 wires are only for a compressor and the compressor is getting hardwired to the circuit?

If so, then the breaker can be rated max 250% of the FLC in the nec table. For 5HP motor, thats 70a(28a FLC x 2.5).

SO the 50a is fine but you can lower it if you want. I wouldnt go below 30a for 5HP and that may nuisance trip...40a should hold no problem.

 

[PT Doc]

To refresh my memory, these 4 #10 wires are only for a compressor and the compressor is getting hardwired to the circuit?

If so, then the breaker can be rated max 250% of the FLC in the nec table. For 5HP motor, thats 70a(28a FLC x 2.5).

SO the 50a is fine but you can lower it if you want. I wouldnt go below 30a for 5HP and that may nuisance trip...40a should hold no problem.

Yes, this circuit is solely for this compressor. So the 10g wire on the 50 amp circuit is ok? From the panel to the current 14-50 receptacle is 6g wire.

 

[The_Auto_Tech]

My 5HP has a 30a and has never tripped. If you're going to hardwire why not just build up to an old work box and then just use a 10g whip? That's how mine's setup.

 

[PT Doc]

My 5HP has a 30a and has never tripped. If you're going to hardwire why not just build up to an old work box and then just use a 10g whip? That's how mine's setup.

I will need about 12 foot of wiring from wall to motor starter. A whip would not be code because either using a plug or cutting of the male plug. Building up the box is not needed since it's a 2 gang box with plenty of room for the 4 wire connections that will be made. Thanks though.

What brand compressor do you have? It's a true 5hp? What's the full load amps from the motor plate? Seems that it would be tripping if it's a true 5hp.

 

[sberry]

6 and smaller, I think I misquoted someone the other day and said smaller than 6.

 

[wyliesdiesels]

I will need about 12 foot of wiring from wall to motor starter. A whip would not be code because either using a plug or cutting of the male plug. Building up the box is not needed since it's a 2 gang box with plenty of room for the 4 wire connections that will be made. Thanks though.

What brand compressor do you have? It's a true 5hp? What's the full load amps from the motor plate? Seems that it would be tripping if it's a true 5hp.

Typically the FLA(different than NEC FLC) for a true 5hp motor is 20-23 so its entirely possible for a 30a breaker to hold. All depends on in-rush current

 

[metlmunchr]

I've got an 800 amp 208V 3 phase service to my shop, so my single phase voltage is 208 rather than 240. Have 2 compressors, a 10hp 3 phase and a 5hp single phase, and run only the 5hp at least 80% of the time.

FLA on the 5hp is 22 A. It runs on a 30 A breaker, and I haven't had a trip in the dozen plus years its been in use. Compressors are typically set up to start unloaded, and in my experience of using various ones over the last 40+ years, if the compressor becomes harder to start, the first place to look is for a leaking check valve that's bleeding tank pressure and keeping the cylinder heads pressurized which causes the compressor to have to start under a load.

 

[PT Doc]

So can someone answer the following. This circuit is on a 50 amp breaker and is currently on 6g wire. When I terminate the wiring with 10g wiring, the 50 amp breaker is still ok? Don't quite understand why it would be but that makes life easier on me with leaving the 50 amp breaker.

 

[The_Auto_Tech]

I will need about 12 foot of wiring from wall to motor starter. A whip would not be code because either using a plug or cutting of the male plug. Building up the box is not needed since it's a 2 gang box with plenty of room for the 4 wire connections that will be made. Thanks though.

What brand compressor do you have? It's a true 5hp? What's the full load amps from the motor plate? Seems that it would be tripping if it's a true 5hp.

What I meant was running 10g Romex to an old work box on the wall and then using a whip from there. The whip attaches through the old work box plate and then attaches at the compressor hookup. But if you need 12 feet a whip won't work anyways. Compressor is approximately 22amp.

 

[pattenp]

So can someone answer the following. This circuit is on a 50 amp breaker and is currently on 6g wire. When I terminate the wiring with 10g wiring, the 50 amp breaker is still ok? Don't quite understand why it would be but that makes life easier on me with leaving the 50 amp breaker.

Being a hardwire motor circuit the #10 is fine on a 50A breaker, but the supply conductors for a 5HP motor must be rated to at least 35A which means using #10 THHN in flex conduit to the compressor. #10 SO cord is only rated at 30A. If you can get HSJO #10 cord, it is rated at 35A.

 

[PT Doc]

Being a hardwire motor circuit the #10 is fine on a 50A breaker, but the supply conductors for a 5HP motor must be rated to at least 35A which means using #10 THHN in flex conduit to the compressor. #10 SO cord is only rated at 30A. If you can get HSJO #10 cord, it is rated at 35A.

Thank you for clarifying.

 

[wyliesdiesels]

So can someone answer the following. This circuit is on a 50 amp breaker and is currently on 6g wire. When I terminate the wiring with 10g wiring, the 50 amp breaker is still ok? Don't quite understand why it would be but that makes life easier on me with leaving the 50 amp breaker.

yes, the larger breaker is ok because it is only providing ground fault and short circuit protection on most motor circuits. The circuit wire and motor is protected by the overloads in the motor starter or overloads integral to the motor.

MOST smaller motors have integral protection. If they dont then they should be wired with a motor starter.

 

[PT Doc]

yes, the larger breaker is ok because it is only providing ground fault and short circuit protection on most motor circuits. The circuit wire and motor is protected by the overloads in the motor starter or integral to the motor.

MOST smaller motors have integral protection. If they dont then they should be wired with a motor starter.

Thanks for the detailed explanation.

 

[wyliesdiesels]

Thanks for the detailed explanation.

The reason i brought up hardwiring in #17 is because if the motor is NOT going to be hardwired and instead cord and plug connected, then the breaker MUST match the outlet/plug rating...

 

[The_Auto_Tech]

The reason i brought up hardwiring in #17 is because if the motor is NOT going to be hardwired and instead cord and plug connected, then the breaker MUST match the outlet/plug rating...

Absolutely makes sense. Do you have any clarification on why they say these things must be hard wired? I have an electrician friend that says using a plug is fine as long as it's all rated for the proper amperage.

 

[mm08822]

Absolutely makes sense. Do you have any clarification on why they say these things must be hard wired? I have an electrician friend that says using a plug is fine as long as it's all rated for the proper amperage.

Plugs and receptacles must be hp rated at or greater than that of the connected motor loads. Same for disconnects, starters, ps used in motor ckts. Amperage rating is not the determining factor of whether a device is suitable for use in a motor ckt.

As for hard wired - virtually any motor can be connected via plug and receptacle. However, the NEMA configured plugs/recepts are only good for 2-3 hp. You need to go up to pin and sleeve style hardware which is $$$$. A pin & sleeve plug/recept/backbox can easily be over $1,000 - more $ than the compressor. So for that reason, the default answer is hardwire.

 

[The_Auto_Tech]

Plugs and receptacles must be hp rated at or greater than that of the connected motor loads. Same for disconnects, starters, ps used in motor ckts. Amperage rating is not the determining factor of whether a device is suitable for use in a motor ckt.

As for hard wired - virtually any motor can be connected via plug and receptacle. However, the NEMA configured plugs/recepts are only good for 2-3 hp. You need to go up to pin and sleeve style hardware which is $$$$. A pin & sleeve plug/recept/backbox can easily be over $1,000 - more $ than the compressor. So for that reason, the default answer is hardwire.

I forgot to clarify - he said using a plug was fine on my heater, which isn't a motor. Never knew that there was a HP rating for plugs and receptacles. That's cool to know! My compressor is hardwired, so I guess I'm good there.

 

[PT Doc]

I forgot to clarify - he said using a plug was fine on my heater, which isn't a motor. Never knew that there was a HP rating for plugs and receptacles. That's cool to know! My compressor is hardwired, so I guess I'm good there.

If you need simple motor rated swithces, check out leviton. They make switch enclosures that make for a clean install. The switch item numbers are like ms602 for a 60 amp single phase. Ms603 would be the 3 phase version.

 

[The_Auto_Tech]

If you need simple motor rated swithces, check out leviton. They make switch enclosures that make for a clean install. The switch item numbers are like ms602 for a 60 amp single phase. Ms603 would be the 3 phase version.

Thanks!

 

[PT Doc]

I had an interesting discussion today with a gentleman that has finished out substantial amounts of commercial space but is not an electrician himself. I explained how I completed the wiring on my compressor and he was not certain it was done right. Since I cannot personally quote NEC tables I kind of was unable to thoroughly explain the reasoning behind how this motor circuit was wired. I did end up keeping the 50 amp breaker an the 6-3 Romex that went to the double Gang Box in the wall. From the wall I completed the wiring with number 10 THHN wiring. He stated that the breaker could not be 50 amps based on the number 10 wiring. I stated that it could be because it was a motor circuit. Does anybody know the NEC table number that I could point the gentleman to so that he could get clarification on this? I have full confidence in how this is wired. But it could be helpful to share this information with somebody that does not. Thanks

 

[wyliesdiesels]

There is no table.

He like many other novices are hung up on 240.4(D)

You can point him to 240.4(G) IIRC...

 

[pattenp]

Also look at 430.52 for the sizing of breaker for a motor circuit. Remember the overload protection is provided at the motor. The breaker size being able to be larger than normal is because it's only providing short circuit protection. If a plug and receptacle was being used for connecting the motor to the circuit then the breaker can be no larger than the smallest wire used in the circuit, so the #10 wire would limit the breaker to 30A in that case. Being hardwired allows the breaker to be sized by 430.52.

 

[PT Doc]

There is no table.

He like many other novices are hung up on 240.4(D)

You can point him to 240.4(G) IIRC...

Also look at 430.52 for the sizing of breaker for a motor circuit. Remember the overload protection is provided at the motor. The breaker size being able to be larger than normal is because it's only providing short circuit protection. If a plug and receptacle was being used for connecting the motor to the circuit then the breaker can be no larger than the smallest wire used in the circuit, so the #10 wire would limit the breaker to 30A in that case. Being hardwired allows the breaker to be sized by 430.52.

Thank you. This should help him get a better understanding. I should read it as well.

It was mentioned in a response in this post that you can increase the breaker size to 250% of the fla. I watched a video where an electrician explained that you have to use the 28a that a 5 hp motor should be when running numbers and not what your motor plate says. Found that interesting as well. Actually I find a lot of this interesting.

Thanks you again for your help.

 

[PT Doc]

https://www.mikeholt.com/mojonewsar...s-Motor-Circuits-and-Controllers~20031126.htm

Some good reading.