Wiring a compressor with a magnetic starter.

[pharmer1]

I recently purchased a used 80 gallon single phase compressor. I installed a new 30 amp breaker in my electrical panel and ran 10-2 Romex to a disconnect near the compressor. From the disconnect I'm running a 4' piece of 10-2 Romex to the compressor.

The compressor came with a magnetic starter and I'm not sure where to connect my black and white wires. To complicate things, there are two red wires and a mystery black wire. See pics attached.

My questions are:
1) where do I connect my black and white wire.
2) where do I connect the two red wires.
3) where do I connect the mystery black wire.


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[pharmer1]

Higher resolution pics: http://imgur.com/a/Xg04z

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[manwithtools]

A couple things first:

What HP is the motor, contactor is rated for up to 7.5 hp at 230 VAC? Supply wiring and circuit breaker might be different than your plan depending on HP.

I would use Liquid tight or BX from your disconnect to the motor starter box, not Romex.

It looks like an EMT fitting that the motor cable is run though, that should be a NM clamp at the least (like the one going into the motor terminal box), more correctly a CGB to use with the SO cord.

That is not the original contactor for that starter box, someone replaced the Eaton = somewhere along the way.

That being said:

The motor starter box should be vertical, not horizontal. They will work like it's shown but are not designed to be that way.

Your incoming power leads will land on L1 and L2 of the contactor. The mystery black wire will connect to L3.

The red wire connected to the lower of two fuses connects to L1 along with your incoming wire. The other red wire from the top fuse connects to L2 along with your other incoming power lead.

 

[nadogail]

.....
The red wire connected to the lower of two fuses connects to L1 along with your incoming wire. The other red wire from the top fuse connects to L2 along with your other incoming power lead.

IMHO, What he said about your Red Wires is "Spot On".

 

[wyliesdiesels]

Thats a 3 phase contactor and overload relay. If the overload relay has phase loss detection then u will need to run T2 from the contactor through the T2 on the overload and back up to L3 then connect motor L2 to T3 on overload relay.

Yes please tell us the HP rating.

This is a total hodge podge. Looks like it got water in it. Are u sure it works?

EDIT: looks like someone already wired in the jumper from T2 to L3...

 

[manwithtools]

EDIT: looks like someone already wired in the jumper from T2 to L3...

Except one end of the jumper has not been landed on L3 yet, hence "The mystery black wire will connect to L3" comment. It's important the OP do this or it will not work.

 

[pharmer1]

Its a baldor 5 HP single phase motor. I ran the Romex through that grey flexible conduit down the wall to the disconnect and from the disconnect to the compressor.

Interesting note, the guy I bought the compressor from said it was hooked upto a three phase panel. I just assumed he was mistaken because the motor clearly says single phase. I'll see if I can find a pic of the motor when I get home. Thanks for all the advice, really appreciate it.

 

[engineer2]

Some Baldor 5 HP single phase motors will run on 2 phases of 208 3 phase. Maybe that's how the guy had it hooked up. If so, the motor data plate will have a spec for 230 VAC as well as 208 VAC. In any case, you hook up to L1 and L2 plus a ground wire.

 

[manwithtools]

Some Baldor 5 HP single phase motors will run on 2 phases of 208 3 phase. Maybe that's how the guy had it hooked up. If so, the motor data plate will have a spec for 230 VAC as well as 208 VAC. In any case, you hook up to L1 and L2 plus a ground wire.

You are not leading this in the right direction. Almost any single phase 230 volt motor will run on two legs of 208 because motors typically have a voltage tolerance of +/- 10% and 208 is just about 90% of 230.

If this is not the case here, you are going to confuse this to no degree. It's not relevant to his situation. This is a case of the starter being wired to single phase, the lower schematic in his photo shows that as does the T2 to L3 jumper wire that needs terminated. The motor is already wired to the starter, his question is about how to wire incoming power to the starter.

Just to be sure, I hope the OP posts pictures of the motor nameplate, but I'm absolutely sure it's single phase.

Edit: No need for name plate pictures. It's clearly single phase.

 

[engineer2]

You are not leading this in the right direction. Almost any single phase 230 volt motor will run on two legs of 208 because motors typically have a voltage tolerance of +/- 10% and 208 is just about 90% of 230.

Except newer Quincy compressors and probably many other brands of motors. I was just answering his part of the question about the original owner running it on a 3 phase system. I would GUESS that the mystery wire goes to L3, but without researching the cutler hammer C306DN3 wiring diagram, I don't want to put that out there as a definitive answer.

 

[manwithtools]

Except newer Quincy compressors and probably many other brands of motors. I was just answering his part of the question about the original owner running it on a 3 phase system. I would GUESS that the mystery wire goes to L3, but without researching the cutler hammer C306DN3 wiring diagram, I don't want to put that out there as a definitive answer.

Which motors are you referring too? I've yet to see a 230 volt or any motor voltage that wont accept +/- 10%. I've got a new 5hp single phase Quincy in the shop BTW.

There is no guessing here. If you study the pictures and the motor starter and it's associated circuity it's obvious. The C306DN3 wiring diagram is not a part of this, it's a simple dedicated purpose contactor that is borderline for this application. It's a three phase contactor wired to function in a single phase application in concert with the overload.

The original owner was spouting BS about running on three phase - did you notice there are only two un-grounded conductors going to the the motor?

 

[Norcal]

You are not leading this in the right direction. Almost any single phase 230 volt motor will run on two legs of 208 because motors typically have a voltage tolerance of +/- 10% and 208 is just about 90% of 230.

If this is not the case here, you are going to confuse this to no degree. It's not relevant to his situation. This is a case of the starter being wired to single phase, the lower schematic in his photo shows that as does the T2 to L3 jumper wire that needs terminated. The motor is already wired to the starter, his question is about how to wire incoming power to the starter.

Just to be sure, I hope the OP posts pictures of the motor nameplate, but I'm absolutely sure it's single phase.

No need for name plate pictures. It's clearly single phase.

A comment about running a 230V rated motor on 208V, besides being a code violation, it's at the bottom end of allowable VD, had better hope that not subject to major voltage dips.

 

[Mr. T]

The original owner was spouting BS about running on three phase - did you notice there are only two un-grounded conductors going to the the motor?

Running 240V single phase equipment on two legs of a 240/120V delta three phase service is very common practice. Just because you have three phases doesn't mean you need to use all of them. Heck, if you're using the 120V on that service you're only using half a leg.

To the OP: I'm sure that combo probably works (if they're sized properly) but it'd be very tempted to replace it with something a little newer/ideal for this use.

 

[manwithtools]

Norcal,
I'm not advocating a 230 motor on 208, just trying to dispel the information in post #8.

230 motors will run on 208 as you know and obviously voltage sags could be a problem. I assume you are referring to 110.3(B)

 

[manwithtools]

Running 240V single phase equipment on two legs of a 240/120V delta three phase service is very common practice. Just because you have three phases doesn't mean you need to use all of them. Heck, if you're using the 120V on that service you're only using half a leg.

To the OP: I'm sure that combo probably works (if they're sized properly) but it'd be very tempted to replace it with something a little newer/ideal for this use.[/QUOTE

You are saying running single phase when you have three phase available is common on motors? Have you heard of the square root of three?

Did you look at the starter wiring?

 

[wyliesdiesels]

Ive seen nameplates that say "can run on 208v system if current doesnt exceed X amount"...

Yes any single phase 240v motor will run on 240v delta 3 phase or single phase 480v motor will run on 480Y or 480D 3 phase service....

 

[Mr. T]

You are saying running single phase when you have three phase available is common on motors?

In an ideal world if you have three phase available you'd be running three phase motors. Just saying it's not immediately a BS statement that it was hooked up to a three phase service.

Maybe the original owner got it on the cheap and figured "what they heck, it's adequate for what I need and I can make it work"?

And I agree that most 240V motors I've come across are also rated for 208V on the nameplate.

 

[pharmer1]

More pics


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[pharmer1]

I'm gonna finish the wiring tomorrow and I'll post pics. My goal is to get this thing running by the weekend. Gotta change the timing belt in my truck and air tools will make my life much easier.

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[Norcal]

You must be in Canada.


EDIT!!!!!!!!!

A grounding conductor is NEVER fused, or switched,as it sits it is very dangerous.

 

[pharmer1]

You must be in Canada.


EDIT!!!!!!!!!

A grounding conductor is NEVER fused, or switched,as it sits it is very dangerous.

Lol watched a YouTube video of a guy that wired his compressor that way. I assumed it would be okay to use that third pole for the ground.

What do you suggest for the ground? Can I simply marette the grounds together?


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[wyliesdiesels]

Lol watched a YouTube video of a guy that wired his compressor that way. I assumed it would be okay to use that third pole for the ground.

What do you suggest for the ground? Can I simply marette the grounds together?


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Yes thats a HUGE NO NO! Very bad!

Since the EGCs are cut short u will need 2 wire nuts, a piece of #10 and a green ground screw. Tie each end together to the piece of #10, then take a second piece of #10 and go from one of the wire nuts to the green ground screw which should be screwed into the disconnect. If there isnt a pre punched hole then u will need to tap one.

By the way since your motor is 5HP, #10 NM-b is too small by code. U shouldve used either #8 NM-b or #10 THWN. Wire for motor circuits is sized @ 125% of NEC FLC table amps, which for a 5HP motor is 28a. 28 * 125% = 35a rated wire.

 

[Norcal]

Lol watched a YouTube video of a guy that wired his compressor that way. I assumed it would be okay to use that third pole for the ground.

What do you suggest for the ground? Can I simply marette the grounds together?


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You just learned that You Tube is a good place learn how to do it wrong.

Attach a lug or screw (after removing the paint where it will be) to to the box, use a wire nut or in Canukistani, "Marrete"to connect the grounding conductors together, they need to bond the enclosure to the grounding conductor(s). Just my opinion but the flex between the disco & the compressor should use stranded conductors because of vibration.

 

[Norcal]

Does anyone know if the CEC rules are the same or similar to the NEC on motors?


The FPE disco, & later the use of the word "Marrete" leads me to think the OP is Canadian.

 

[engineer2]

I've yet to see a 230 volt or any motor voltage that wont accept +/- 10%. I've got a new 5hp single phase Quincy in the shop BTW.

We've burned up a couple of 230 VAC compressor motors running them on 208. They work as long as the power company never has issues with voltage levels. It's all a moot point since the OP isn't going to have 208.

That fused ground sure is scary. Since the Cutler Hammer box cover has the wiring, go by that. As stated, #10 THWN is probably OK for home use, but #8 is a better choice.

 

[pharmer1]

Corrected the ground on the disconnect and wired it according to the advice here. Haven't started it up yet. Have to change the oil first.

How does the wiring look?



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[Mr. T]

Just to be nit picky I'd tape the white wires black or red since they aren't really a neutral. Other than that, hope it works for years.

 

[engineer2]

Methinks the grounds in your on-off switch box should all be tied together on a grounding block that is attached to the panel, but maybe one of the electricians here can chime in with what is acceptable.

 

[pharmer1]

It was an old disconnect. I drilled and tapped the ground screw. Then scrapped the paint off of the box before I screwed the ground to the box.

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[matt_i]

I may have missed something but I don't understand why phase loss/overload protection is being used in single phase service. Just eliminate that (white, Siemens?) component, fuse and breaker properly, and go on with life.

My guess is you will eventually end up jumpering the NC contact anyway.

In other words, in my opinion, its a component that isn't doing its real function, is potentially unreliable used like this as the amperage per leg or phase is different from 1ph to 3ph, and an additional troubleshooting roadblock. Simplest solution: eliminate it.

 

[cbogg]

I'm surprised no one mentioned the Romex in flexible conduit thing.....

 

[wyliesdiesels]

I may have missed something but I don't understand why phase loss/overload protection is being used in single phase service. Just eliminate that (white, Siemens?) component, fuse and breaker properly, and go on with life.

My guess is you will eventually end up jumpering the NC contact anyway.

In other words, in my opinion, its a component that isn't doing its real function, is potentially unreliable used like this as the amperage per leg or phase is different from 1ph to 3ph, and an additional troubleshooting roadblock. Simplest solution: eliminate it.

Yeah u missed the part about the starter being used/reused from another setup.

Jumpering the phase loss relay wont cause any issues. It doesnt care that the amperage is higher with a single phase motor. All it cares about is that the current running through the legs measure equally.

BTW I have seen new single phase compressors come from the factory with 3 phase starters and phase loss relays with the center T2 leg jumpered over to L3.

I'm surprised no one mentioned the Romex in flexible conduit thing.....

NorCal allided to it by saying that stranded THWN wire shouldve been used.

 

[pharmer1]

Update:
I changed the oil and flipped the breaker on and turned the disconnect to the on position and nothing. I guess it's better than sparks flying and parts exploding.
First thing I did was test all fuses for continuity and they were all good. Back to square 1. Any chance the disconnect is bad?

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[pharmer1]

Doh! Rookie mistake, I had the breaker plugged into a single leg of the panel. Dropped the breaker down 1 spot to span both left and right has sides of the panel, flipped the breaker to the on position and she purrs like a cat.

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