Multiple Motors, Single Circuit

[infinity]

Can you have a single circuit installed for 3-480 volt, 10 HP motors with the conductors field spliced to three separate motor contactors all housed in one enclosure? I have a situation where one circuit was installed to a control cabinet but the motor starters integral to the cabinet are set up for three individual circuits.

 

[augie47]

If I understand it correctly, IMO, No you can't.
430.52 would limit your GFSC device for any one 10 HP motor to 35 amps max which would be insufficient for the load of the 3 motors.

If your motor starters are of the type that GFSC is included (such as some IEC equipment), it might be possible.

 

[infinity]

If I understand it correctly, IMO, No you can't.
430.52 would limit your GFSC device for any one 10 HP motor to 35 amps max which would be insufficient for the load of the 3 motors.

If your motor starters are of the type that GFSC is included (such as some IEC equipment), it might be possible.

My thought as well. Since the three starters have no individual OCPD then a tap won't work unless three taps with separate a OCPD for each tap is used.

 

[hurk27]

Are you saying you have starters that do not provide any overload protection for each motor? are these just contactors without overloads? I'm confused because a motor starter without overloads is not a motor starter?

unless the motors are internally protected they will need overload protection 430.32 will require it for motors over 1hp, the cabinet will need a disconnect, but I don't see where 430.24 can't be used? or 430.53 for multiple motors?

430.52 is only for a single motor on a branch circuit, I don't see where it applies to multiple motors?

 

[hurk27]

I guess my thinking on this is the motor starters would have to have overloads sized for each motor, unless fuses are used for each starter sized for the GFSC then the conductors to each motor would be required sized to be the same as the circuit feeding the cabinet (430.53(D)(1)

If fuses are installed for each motor controller then we have feeders.

Most of the motor controler cabinets I have built allways has a main disconnect for the cabinet, each motor controller has OCPD, fuses or breaker for each controler, each controler will have overloads to protect the motor, never seen an installation done other wise?

 

[infinity]

There is overload protect but not individual short circuit or ground fault protection provided by an OCPD ahead of the each starter. Basically you have a control panel designed for three motors with an individual circuit for each motor. Electrical drawing showed a single control panel with one circuit feeding the entire panel so only one circuit was pulled. Now they want to simply splice onto the larger circuit conductors (#4 I believe) with #10's and feed the three motor starters within the control panel.

 

[texie]

IMO, not compliant as others have said. In addition the motor conductors not having GFSC protection, the starters likely would not be protected per the manufacturer either. I would say you need 3 properly sized branch circuits.

 

[Jraef]

There is overload protect but not individual short circuit or ground fault protection provided by an OCPD ahead of the each starter. Basically you have a control panel designed for three motors with an individual circuit for each motor. Electrical drawing showed a single control panel with one circuit feeding the entire panel so only one circuit was pulled. Now they want to simply splice onto the larger circuit conductors (#4 I believe) with #10's and feed the three motor starters within the control panel.

This concept is used all the time, but for MUCH SMALLER MOTORS. The reason is because if you are dealing with 3 x 1-1/2HP 460V motors that each are 3.0A FLC, then all 3 loads together still are small enough to fit behind #14 wire, the minimum size anyway, and a 15A circuit breaker.

The #4 conductors are (I assume without looking) OK, especially in that you will need a larger feeder for that circuit because of the potential of 3 fully loaded 10HP motors on it, i.e. 52A minimum. So assuming a 70A breaker, that becomes your GF/SCPD for the ENTIRE circuit. The individual OLs can count as the OCPD for the motor conductors, but not the GFSC device. So that means that TECHNICALLY, this can only work like this if you run the #4 all the way down to the motors, which will most likely be a big problem once you get to the motor peckerhead.

One way to do this though is to use the IEC style Motor Protective Switches that each have the necessary circuit components. They are the SCPD, the OL and a Disconnect device all in one. So that plus a plain contactor makes an individual Combination Motor Starter for each circuit. There are other rules that you must pay attention in the NEC if you do this, but it is possible.