Shop Floor Talk

Shop Floor Talk (https://www.shopfloortalk.com/forums/index.php)
-   Mechanical & Electrical (https://www.shopfloortalk.com/forums/forumdisplay.php?f=36)
-   -   Proper Wiring of a Motor Starter (https://www.shopfloortalk.com/forums/showthread.php?t=52717)

Lowe.Buuck 12-29-2020 03:16 AM

Proper Wiring of a Motor Starter
 
1 Attachment(s)
The single phase 5hp motor on my compressor died from a shorted field. I have another single phase 5hp TEFC motor that I got mounted.

My issue is the replacement motor draws more amps than the pressure switch can handle.

I picked up a used Eaton Freedom Series motor starter with an overload relay. The overload relay is adjustable and will match the motor FLA. It is a NEMA Size 2 rated for 7.5hp at 240v and has a 120v coil.

The only thing that tested bad was the auxiliary NO side mount contact has high resistance when closed. So I removed it.

I have attached a pdf of what I think is the correct wiring. If the overload trips it not only opens the feed to the motor but also opens the power to the contactor coil. The overload is set to Manual Reset.

Can anyone see any issue with my plan?

Is there a better or more correct way to wire this?

GWIZ 12-29-2020 04:35 AM

Should work, but I would move the fuse to feed from the start of L1 otherwise you still have power in half the circuit if it blows and does not protect points 95,96

Bear in mind with this setup if power is interrupted the compressor can re-start on its own when power is restored.

460 Delta 12-29-2020 07:06 AM

Looks ok but as mentioned the fuse needs moved before the pressure switch.

Lowe.Buuck 12-30-2020 01:28 AM

Thanks to both of you for responding.

I've wired contactors, but had never seen an overload relay.

I pulled out the multimeter and determined the function of the accessory terminals and tried to deduce their use.

I also need to run a 10ga feed. One more thing to do...

Again thanks!

460 Delta 12-30-2020 07:43 AM

Quote:

Originally Posted by Lowe.Buuck (Post 765755)
Thanks to both of you for responding.

I've wired contactors, but had never seen an overload relay.

I pulled out the multimeter and determined the function of the accessory terminals and tried to deduce their use.

I also need to run a 10ga feed. One more thing to do...

Again thanks!

The aux contacts if NO are usually used for the latch on a momentary pushbutton start-stop setup. If they are NC, it is likely for some interlocking scheme, for example if this is running, that can't be started.

Norcal 12-30-2020 08:48 AM

If you use NM cable 10 AWG is too small, code requires minimum of 35A conductors for a 5 HP single phase motor, as they are not sized per nameplate values (unless higher) but by 125% of table 430.248 which is listed as 28A at 230V, 125% of that is 35A, for motors 10 AWG THHN is 35A, or 8 AWG NM cable which is 40A, since NM cable must sized from the 60° column of table 310.15(B)(16), dual rated THHN THWN 10 AWG is 35A, and special permission is given for motors to use it at that given value for motors, with normal circuits 10 AWG is limited to 30A.

Lowe.Buuck 12-31-2020 12:27 AM

Norcal or any others,

430.22 references a single motor in continuous duty application. Since this compressor operates intermittently, is it classified as a Motor Operated Appliance and does 430.6(A)(1) Exception 3 apply?

The previous motor's nameplate had it as 5 Hp Spl with a FLA of 20A. The current motor's nameplate shows 5 HP, FLA of 23A. Does the NEC address the issue of motors "overstating" the HP in comparison to the FLA?

I am not an electrician. I have a 2002 copy of the NEC, but I had never read Article 430 until now.

I appreciate your responses and as I attempt to get a better understanding of this material.

Here I thought I just needed to run a new 3 wire feeder so I had a neutral to support the 120v coil in the contactor.

GWIZ 12-31-2020 04:55 AM

I'm on the repair side of things, not an installer so I'm not up on the new codes.
A few years back a guy comes over and asks if he can borrow my A/O torch.
people changing out his AC pump motor ran out of Acetylene the person figures it maybe a week before they come back with Acetylene.
Anyway I like to see what they are doing.

Old motor looked fairly clean so I looked at some of the wiring, I was a bit shocked!
In my opinion the wire was quite a bit under-sized for a three-phase roof mount AC pump motor.
Looked at the name plate, on AC units the manufacture has a wire size call out and was correct for what was installed.
Don't recall a length call out.

Just me
I got to thinking about this under size wire call out,
I recalled that a lot of these 240 volt AC units have motors burn-up withing 8-15 years, but yet 120v and home refrigerators rarely burn-up a motor pump.
My opinion its a scam that allows the A/C manufacture to place a label that states under size wire.

In your case If your 10ga wire is less then 20 feet it will likely work, any longer than that your motor may have a shorter life.
5hp air-compressor pump motors really need that +60 amp starting power. too much of a delay starting takes it toll using smaller wire.
Starting Amps for a 5hp motor can be over 150 amps.

A short is not quite a burn-up, how long did your old motor last with your current wiring?

gauge size is one thing but the wire length is just as important.

Lowe.Buuck 12-31-2020 08:29 PM

Quote:

Originally Posted by GWIZ (Post 765810)
A short is not quite a burn-up, how long did your old motor last with your current wiring?

gauge size is one thing but the wire length is just as important.

The motor was 15+ years old. In that period I replaced the centrifugal switch, a start cap and a pressure switch. The motor was not a high quality motor, just a Compressor Duty, Open Drip Proof, Cap-Start/Cap-Run 3450 rpm from Northern Tool.

The wire feeding it was a 18ft SJEOW 10/2 with an inline circuit breaker box that was plugged into one of my welder receptacles.

The compressor was in my garage, adjacent to my shop. Not enclosed but away from grinding dust and saw dust.

The compressor head is a Quincy QTS-5, 4 cylinder single stage with a horsepower range of 3-5 hp. A 5 hp motor should not be overly stressed in this application.

The replacement motor is a Farm Duty 184 frame TEFC 1740 rpm. Dimensionally larger and weight is much heavier. I don't know what the start amps will be, but the pulley on this motor 6.75" to get the compressor to 90% of its max rated rpm. I suspect the larger pulley may demand a higher starting amps.

Norcal 01-01-2021 11:46 AM

1 Attachment(s)
Quote:

Originally Posted by GWIZ (Post 765810)
I'm on the repair side of things, not an installer so I'm not up on the new codes.
A few years back a guy comes over and asks if he can borrow my A/O torch.
people changing out his AC pump motor ran out of Acetylene the person figures it maybe a week before they come back with Acetylene.
Anyway I like to see what they are doing.

Old motor looked fairly clean so I looked at some of the wiring, I was a bit shocked!
In my opinion the wire was quite a bit under-sized for a three-phase roof mount AC pump motor.
Looked at the name plate, on AC units the manufacture has a wire size call out and was correct for what was installed.
Don't recall a length call out.

Just me
I got to thinking about this under size wire call out,
I recalled that a lot of these 240 volt AC units have motors burn-up withing 8-15 years, but yet 120v and home refrigerators rarely burn-up a motor pump.
My opinion its a scam that allows the A/C manufacture to place a label that states under size wire.

In your case If your 10ga wire is less then 20 feet it will likely work, any longer than that your motor may have a shorter life.
5hp air-compressor pump motors really need that +60 amp starting power. too much of a delay starting takes it toll using smaller wire.
Starting Amps for a 5hp motor can be over 150 amps.

A short is not quite a burn-up, how long did your old motor last with your current wiring?

gauge size is one thing but the wire length is just as important.

Attachment 159054

That label is not a "scam" the manufacturer has calculated the load of the equipment plus added the required 125% so the electrician sizes the conductors based on 22A, so if using NM cable, 10 AWG is required since NM cable is sized from the 60° column of table 310.15(B)(16), but article 440 allows the values of the same table to be used, so if THWN THHN conductors are used, 12 AWG has a ampacity of 25A, it does not have the limitations of a normal branch circuit of 20A, so in that application 12 AWG THWN is code compliant, and because the compressor has overload protection, the fuses or circuit breaker is just for short circuit protection, it can have a 35A fuse or circuit breaker, if the label only mentions fuses then only fuses can be used, but that was found on older equipment, rare now. With motors and A/C units, wire and fuse/circuit breaker combinations that would not be allowed on a normal branch circuit is code compliant for those applications.

GWIZ 01-07-2021 11:41 PM

Quote:

Originally Posted by Norcal (Post 765867)
Attachment 159054

That label is not a "scam" the manufacturer has calculated the load of the equipment plus added the required 125% so the electrician sizes the conductors based on 22A,

Not being specific to TRANE

there was two labels. I'm talking about a label that the "Manufacturer" states what wire size to use. I don't see a wire size listed in the label you posted.


All times are GMT -5. The time now is 01:07 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.