Ats and MCC conductor question

[kouta]

We have a 260A ATS switch that is fed from a 250kcmil 3c cable. It powers 26 different loads currently daisy chained together and they are moving the loads to an 480v MCC instead to isolate all the loads using the same power source. The incoming power to mcc was spec'd for 2 500kcmil 3c. Is this ok?

 

[iwire]

We have a 260A ATS switch that is fed from a 250kcmil 3c cable. It powers 26 different loads currently daisy chained together and they are moving the loads to an 480v MCC instead to isolate all the loads using the same power source. The incoming power to mcc was spec'd for 2 500kcmil 3c. Is this ok?

You did not provide any current information of the loads so how can we say?

 

[kouta]

There are also spares in addition to the original 26 loads. Some are starters and some are feeder breakers.


The breaker trip or fuse load amps
2 X 3A
4 X 30A
7 X 40A
2 X 50A
3 X 100A
5 X 15A
4 X 20A
4 X 7A

 

[augie47]

There are also spares in addition to the original 26 loads. Some are starters and some are feeder breakers.


The breaker trip or fuse load amp
2 X 3A
4 X 30A
7 X 40A
2 X 50A
3 X 100A
5 X 15A
4 X 20A
4 X 7A

almost meaningless... you need actual load information and knowledge of load diversity.
listing the breakers is akin to listing all the breakers in a residential panel and thinking you need a 600 amp service based of the sum of the breakers.
side note. Hopefully your cables are 3/c + equipment ground. If so, check your grounding conductor size relative to the OCP protecting the cable.
Paralleling cables often leads tom undersized equipment grounds.

 

[kouta]

The actual load sizes are
3 x 3hp
5hp
3hp
.75hp
2 x 40hp
3 x 10hp
3 x 1.5hp
1hp

 

[iwire]

The actual load sizes are
3 x 3hp
5hp
3hp
.75hp
2 x 40hp
3 x 10hp
3 x 1.5hp
1hp

Do you understand how to do load calculations found in articles 220 and 430?

You need to look up the NEC FLA of each of those motors and do the feeder calculations to determine the actual load connected to the MCC.

Than there is also the possibility that some loads may not run at the same time or some loads could be locked out when power is coming from the generator.

Not trying to give you a hard time but the question you are asking is far from easy to answer without a full overview of the job.

 

[kouta]

Do you understand how to do load calculations found in articles 220 and 430?

You need to look up the NEC FLA of each of those motors and do the feeder calculations to determine the actual load connected to the MCC.

Than there is also the possibility that some loads may not run at the same time or some loads could be locked out when power is coming from the generator.

Not trying to give you a hard time but the question you are asking is far from easy to answer without a full overview of the job.

Thanks, I have the full load amps of each motor but I have not done the feeder calculations. I will consult the articles. I just have a drawing for the mcc that had the previous information I posted.

 

[augie47]

You really should run the numbers as i-wire suggests, but a quick review shows your 500 cables will be more than adequate.

 

[Jraef]

The MCC doesn't matter. You have a 260A rated ATS, that's your limit right there. So the only question is, can you use 2x 500kCMIL cables per phase to feed a 260A load? Probably yes, but we don't know your other conditions at the site. Assuming copper, 75C insulation, normal temperature, reasonable distance, no more than 2 conductors in each conduit, each of your 500s is rated for 380A. You likely don't even need 2 per phase...

 

[kouta]

The MCC doesn't matter. You have a 260A rated ATS, that's your limit right there. So the only question is, can you use 2x 500kCMIL cables per phase to feed a 260A load? Probably yes, but we don't know your other conditions at the site. Assuming copper, 75C insulation, normal temperature, reasonable distance, no more than 2 conductors in each conduit, each of your 500s is rated for 380A. You likely don't even need 2 per phase...

Thanks, They are actually going with single phase now since it was all that was required.