2 motors on one starter

Status
Not open for further replies.
I have an existing soft start running a 200 hp motor a couple of times a week. Can I install a 200Amp fused disconnect and run a 125 HP motor from the same starter? This motor is also a part time motor. I plan to interlock the disconnect as well as installing separate start/stop buttons for the new motor. A new run relay will also be installed and interlocked to prevent both motors from running.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have an existing soft start running a 200 hp motor a couple of times a week. Can I install a 200Amp fused disconnect and run a 125 HP motor from the same starter? This motor is also a part time motor. I plan to interlock the disconnect as well as installing separate start/stop buttons for the new motor. A new run relay will also be installed and interlocked to prevent both motors from running.
I suspect you would be out of compliance with the NEC if you did this for the reason cited by another poster and because the over current device appropriate for the 200HP motor probably is not appropriate for the 125HP motor.

I am not sure what you are referring to as a run relay.
 

VinceS

Senior Member
Reservations...

Reservations...

1. I have done this type of install before, but only with a rated transfer switch as a disconnect to the motor. I installed Early break switch's on both positions. Isolation was done with a monitoring relay which was tied into both O/L devices and there respective control circuits. The operator control indicated which motor was running and was able to start and stop / E-Stop either motor from each required station.

2. The Ramp to start must work for both motors. You might also consider using a mechanically interlocked relay as a latch for each starting signal to the softstart.

3. In the end this install costs nearly as much as a new softstart, provided you have a empty bucket in your MCC to start it.

4. This type of install meets requirements of 430.24 note exception #3.

5. Take care to post instructions and warnings to the electricians and operators which come after you.
 
Last edited:
I have an existing soft start running a 200 hp motor a couple of times a week. Can I install a 200Amp fused disconnect and run a 125 HP motor from the same starter? This motor is also a part time motor. I plan to interlock the disconnect as well as installing separate start/stop buttons for the new motor. A new run relay will also be installed and interlocked to prevent both motors from running.

Selector switch on the secondary side of the soft start and you would need to readjust the OL settings each time. Since the SC let-through of the SSRV starter is much less than what is available on the lug side I would not worry about the FDSW. If you don't feel comfortable with this setup then install separate OL realy on the 125HP side and adjust it for the FLA of that motor. Use either aux. contacts on the selector switch to activate each set of the individual pushbuttons. If you want to get fancy add an indicating light to the pushbuttons to confirm if the circuit is ready. Or you can use a secondary CPT connected to each side of the selector switch.

If you clarify the reason why SSRV is used there may be other comments pertaining to how you wish to configure your circuits and settings.
 

VinceS

Senior Member
No, add new O/L's

No, add new O/L's

To make this work seperate O/L's MUST be added... Then set the Softstart for the largest load, or discontinue it use,( depends on type of Softstart ).
 

VinceS

Senior Member
It there is a physical disconnect installed so as only one motor can be run, only on motor will be served by the controlling means.
 

VinceS

Senior Member
Yes that was the point I was trying to reenforce... Selector switch = Transfer switch

Edit to earlier post...
"If there is a physical disconnect installed so as only one motor can be run, only on motor will be served by the controlling means."
 
Last edited:

VinceS

Senior Member
Different, but I see the wisdom.

Different, but I see the wisdom.

A Selector switch is not equal to a Transfer switch. A selector switch like a drum stile isn't lockable, but can be made inter-lockable.
Just a difference in design... Your idea would be much cheeper though. I can see its wisdom.
 
A Selector switch is not equal to a Transfer switch. A selector switch like a drum stile isn't lockable, but can be made inter-lockable.
Just a difference in design... Your idea would be much cheeper though. I can see its wisdom.

Hm..Rotary or lever type selector switches both can have locking provisions, although I don't understand why that would make any difference. The lockout provision should be provided on the SSRV disconnecting means.
 
Status
Not open for further replies.
Top