Motor Circuit

[J. O. R.]

I have an existing contrition and conflicting opinions as to whether this is Code compliant or not. Please take a look at the attached PDF and comment on the wire and circuit protection sizing. Is this correct, Why or Why Not?

Thanks!!!

 

[don_resqcapt19]

Possible violation of 240.21(C) for the conductors between the transformer and the MCC as they are over 25' long.

 

[J. O. R.]

This is not a MCC it is a service entrance switchboard, the metering is directly off the transormer and just not shown. The conflicting opinions are in refferance to the circuit comming off of breaker MSB-9

Thanks

 

[iceworm]

I'm not familiar with some of the terminology.

MSB-9 should be a thermal-mag.
ABB S6H could be a mag-only or thermal-mag - I can't tell

I can't tell if there are any overloads or if there are, what are they set at.
Is this ABB S6H some type of soft start?

Maybe what you are asking if it is okay to protect parallel 4/0 with a 500A thermal-mag CB?
If so, that would depend some of the details. As you likely know, specific answers are in art 430.

Either way, I would be surprised a 480V, 300HP motor would start across-the-line on a 500A trip thermal-mag. Is this working now?

the worm

 

[J. O. R.]

ABB S6H (and MSB-9) are Molded Case Circuit Breakers with electtronic tripps, ABB S6H is in a Y/Delta Starter with motor over loads (not sure what they are), Yes it is working now and yes there is a question regarding the prtection of the wire.

Thanks for you response.

 

[iceworm]

ABB S6H (and MSB-9) are Molded Case Circuit Breakers with electtronic tripps, ABB S6H is in a Y/Delta Starter with motor over loads (not sure what they are), Yes it is working now and yes there is a question regarding the prtection of the wire.

Thanks for you response.

That helps:
Most of your answers are in art 430. Some may be in the manual for the ABB starter.

(2008) Art 430.22.C specifies the minimum conductor sizes for the both the controller line side and controller to motor.

Art 430.52.C specifies the max CB size.

You will need to get the motor nameplate current.

Don't forget that if all six conductors are in one conduit there are derate issues.

I would also recomend you get the overload ratings - and read the book on the starter.

the worm

 

[J. O. R.]

Further Clarification

Further Clarification

Thanks for your replies Don & Worm,

Let me shed a little more light on the situation & system (I had asked the question very open/generalized as to not to lead anyone, I wanted honest interpolations/options first). This is an existing system that we are performing an Fault Current, Coordination & Arc Flash Hazard Study on. During a review the existing circuit breaker sizes vs. the wire sizes were questioned and it was suggested that the either the wire sizes or breaker sizes needed to be changed, but this is not everyone?s option. Some believe that from the Switchboard to the Starter cabinet is a feeder others believe this is a Motor Branch Circuit. I can not find in the Code where it makes a clear distinction as to how this particular installation/application would be classified. Any further clarification or comments would be greatly appreciated. See the attached sheets for more detail regarding the existing installation.

 

[david luchini]

Some believe that from the Switchboard to the Starter cabinet is a feeder others believe this is a Motor Branch Circuit. I can not find in the Code where it makes a clear distinction as to how this particular installation/application would be classified. Any further clarification or comments would be greatly appreciated.

If there is a circuit breaker or other OCPD in the Starter Cabinet, then you would have a feeder from the switchboard to the starter. If there is no additional OCPD in the Starter Cabinet, then you would have a branch circuit from the switchboard to the cabinet. A branch circuit is the conductors between the "final" OCPD protecting the circuit and the outlet.

However, it shouldn't make any difference if it was a feeder or branch circuit. It would seem to be properly sized for either case.

 

[iceworm]

Thanks for your replies Don & Worm,

Let me shed a little more light on the situation & system (I had asked the question very open/generalized as to not to lead anyone, I wanted honest interpolations/options first). This is an existing system that we are performing an Fault Current, Coordination & Arc Flash Hazard Study on. During a review the existing circuit breaker sizes vs. the wire sizes were questioned and it was suggested that the either the wire sizes or breaker sizes needed to be changed, but this is not everyone?s option. Some believe that from the Switchboard to the Starter cabinet is a feeder others believe this is a Motor Branch Circuit. I can not find in the Code where it makes a clear distinction as to how this particular installation/application would be classified. Any further clarification or comments would be greatly appreciated. See the attached sheets for more detail regarding the existing installation.

J -
May I again gently suggest you read 430.22.C. I'd say it is a clear as is possible for the code to be.

hint - the conductors between the switchboard and the starter are not a feeder)

the worm

 

[don_resqcapt19]

If it is a single motor, it really doesn't matter if you call it a feeder or a branch circuit. The required wire size is the same in either case and in either case you can use a thermal magnetic OCPD with a rating of 250% of the motor full load current from Table 430.250. In this case the ampacity of the conductors must be at least 451.25 amps. The installed conductors have an ampacity of 460 amps so they are compliant. The maximum permitted OCPD would be 902 amps. The rating of the switchboard OCPD feeding this circuit is less than that.

The above is for the 300 hp motor fed by MSB-9. The other motors also seem to comply with the code rules.

 

[iceworm]

If it is a single motor, it really doesn't matter if you call it a feeder or a branch circuit. The required wire size is the same in either case and in either case you can use a thermal magnetic OCPD with a rating of 250% of the motor full load current from Table 430.250. In this case the ampacity of the conductors must be at least 451.25 amps. The installed conductors have an ampacity of 460 amps so they are compliant. ....

It shouldn't make a difference here, but that changed between the 2008 and 2011. 2008 says to base the conductors on the lineside of the controller on the motor full-load current - not the tables. Controller loadside conductors are based of 58% of the motor flc - again not the tables.

Depending on when it was installed could make a heck of a difference in the regulatory requirements