Electrical Design Question

[Timeismoney08]

I would really appreciate any help with this question and anything pointing to the NEC would be appreciated.

Scenario:
Let's say I have 6 motors and each use 10 amps.. So 60 Amps total fully loaded could possibly be used on my machine.

The machine is being fed from a 30A drop is ran over, so then I fuse my machine at 20A.. I would protect each motor individually at around 10A.

If my program prevents starting multiple motors at a time (Non-safety rated) and all protection is sized not to cause an issue, is this allowed? Obviously if someone went in and forced all of the outputs on, it would blow a breaker, but it that okay?

 

[rupej]

I would really appreciate any help with this question and anything pointing to the NEC would be appreciated.

Scenario:
Let's say I have 6 motors and each use 10 amps.. So 60 Amps total fully loaded could possibly be used on my machine.

The machine is being fed from a 30A drop is ran over, so then I fuse my machine at 20A.. I would protect each motor individually at around 10A.

If my program prevents starting multiple motors at a time (Non-safety rated) and all protection is sized not to cause an issue, is this allowed? Obviously if someone went in and forced all of the outputs on, it would blow a breaker, but it that okay?

I believe so. I don't have the NEC in front of me but I seem to recall there being an exception to the rules if multiple loads were prevented from running at the same time. Check the section on motor power circuits.

 

[Timeismoney08]

I believe so. I don't have the NEC in front of me but I seem to recall there being an exception to the rules if multiple loads were prevented from running at the same time. Check the section on motor power circuits.

Thank you for the response. I will look into that section.

I remember another application where I had 10 * 24VDC actuators all using 10A a piece, but never being used at the same time.. I purchased a 100A of 24VDC PS to be safe, but then in reality it never exceeded more that 6A. Lol.. So it was extreme overkill for the application and caused many headaches and each actuator was fused at 10A, so this is similar, but just this time it's with the incoming power.

 

[baref00t25]

I think you want NEC 430.24 Several Motors

 

[atc222]

UL 508A 49.2 - The full-load ampere rating of the panel shall, at a minimum, include the sum of all loads that are able to be operated simultaneously plus the primary ampere rating of all control transformers connected to the input voltage.

The key is able to be operated simultaneously. Think 25 vfds in an enclosure, but only two at a time run. In the industrial automation world, I was always a fan of trending actual running current of a system, adding a reasonable margin, and marking accordingly. This keeps the customer from having to supply a grossly oversized feeder. Obviously this only works if you're building the complete system in house. Otherwise, you're stuck with calculating it.

 

[Timeismoney08]

I think you want NEC 430.24 Several Motors

Thank you!

 

[Timeismoney08]

UL 508A 49.2 - The full-load ampere rating of the panel shall, at a minimum, include the sum of all loads that are able to be operated simultaneously plus the primary ampere rating of all control transformers connected to the input voltage.

The key is able to be operated simultaneously. Think 25 vfds in an enclosure, but only two at a time run. In the industrial automation world, I was always a fan of trending actual running current of a system, adding a reasonable margin, and marking accordingly. This keeps the customer from having to supply a grossly oversized feeder. Obviously this only works if you're building the complete system in house. Otherwise, you're stuck with calculating it.

Thank you!