Shop Floor Talk  

Go Back   Shop Floor Talk > Welding and Metalworking Forums > Mechanical & Electrical

SFT Search:   
Reply
 
Thread Tools Display Modes
  #1  
Old 12-29-2020, 03:16 AM
Lowe.Buuck Lowe.Buuck is offline
Junior Member
 
Join Date: Jul 2017
Location: Minnesota, USA
Posts: 34
Default Proper Wiring of a Motor Starter

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?
Attached Files
File Type: pdf MotorStarter.pdf (177.6 KB, 61 views)
Reply With Quote
  #2  
Old 12-29-2020, 04:35 AM
GWIZ's Avatar
GWIZ GWIZ is offline
SFT Historian
 
Join Date: Feb 2006
Location: USA
Posts: 7,186
Default

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.
__________________
*
*
The factory of the future will have only two employees, a man and a dog. The man will be there to feed the dog. The dog will be there to keep the man from touching the equipment. ~Warren G. Bennis
Reply With Quote
  #3  
Old 12-29-2020, 07:06 AM
460 Delta's Avatar
460 Delta 460 Delta is offline
Member
 
Join Date: Aug 2020
Location: Southern Ohio
Posts: 53
Default

Looks ok but as mentioned the fuse needs moved before the pressure switch.
__________________
Perfection is the enemy of good enough.
Reply With Quote
  #4  
Old 12-30-2020, 01:28 AM
Lowe.Buuck Lowe.Buuck is offline
Junior Member
 
Join Date: Jul 2017
Location: Minnesota, USA
Posts: 34
Default

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!
Reply With Quote
  #5  
Old 12-30-2020, 07:43 AM
460 Delta's Avatar
460 Delta 460 Delta is offline
Member
 
Join Date: Aug 2020
Location: Southern Ohio
Posts: 53
Default

Quote:
Originally Posted by Lowe.Buuck View Post
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.
__________________
Perfection is the enemy of good enough.
Reply With Quote
  #6  
Old 12-30-2020, 08:48 AM
Norcal Norcal is offline
Elite Member
 
Join Date: Jul 2009
Location: California
Posts: 1,413
Default

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.
Reply With Quote
  #7  
Old 12-31-2020, 12:27 AM
Lowe.Buuck Lowe.Buuck is offline
Junior Member
 
Join Date: Jul 2017
Location: Minnesota, USA
Posts: 34
Default

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.
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Web Search:

All times are GMT -5. The time now is 07:30 AM.


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