Motor control panel

[jjwitty]

Need some guidance for a service feed for a motor control panel.

The 480 panel will feel 9, 3p, 18hp motors and 9, 3p, 5hp motors. Each motor will have 120v control circuit, and the 5hp motors will have a temperature controller.

The 15hp motors are used for pumping oil in/out, the 5hp motors are used to heat up the oil.

Here is the tricky part:
The motors cannot all run at the same time. Only one blender is able to pump at once, and all heat exchangers won't be used at once. What is the minimum service feed we can add for this panel? The contractor we first talked to wants to add a 200 amp service, which would align with the scenario of all motors running at once. That would require a 500' run from our main MCC. Another option is underrating the panel and feeding out of a subpanel, but this needs to be within code.

What is code for the minimum usage? We have existing panels with up to 20 motors on a 100 amp circuit.

 

[don_resqcapt19]

This appears to be asking for advice that will be passed to the installing electrician so I approved the post.

 

[don_resqcapt19]

What actually prevents someone from running all of the motors at the same time? Are there any possible operating conductors that would result in them all running at the same time?

 

[jjwitty]

What actually prevents someone from running all of the motors at the same time? Are there any possible operating conductors that would result in them all running at the same time?

I could add controls to stop this from happening, I would like to see code that could back it up.

I understand there’s always a scenario where somone could come along and turn every motor on. I also understand PLC well enough that I could create interlocks to prevent that from happening.

I would like the contractor to come out of the existing panel if at all possible; however, I am unable to find code to back this installation up. Another contractor mentioned a code that may allow this, but he didn’t cite.

 

[zbang]

That's all very vague.

Two things-
"Service" has a specific meaning, the word you probably need there is "feeder".

The motors cannot all run at the same time.

Cannot because a control system prevents it or should not because bad things will happen (like tripping a breaker)? The minimum feeder size could be small enough to run a 15HP motor and nothing else, you'll have to decide which devices should be allowed to run at the same time and the electrician or an engineer can figure it out from there. And another things that plays in to the calculation is whether the motors are across-the-line started or on some from of speed controller, that affects the starting surge.

 

[jjwitty]

That's all very vague.

Two things-
"Service" has a specific meaning, the word you probably need there is "feeder".


Cannot because a control system prevents it or should not because bad things will happen (like tripping a breaker)? The minimum feeder size could be small enough to run a 15HP motor and nothing else, you'll have to decide which devices should be allowed to run at the same time and the electrician or an engineer can figure it out from there. And another things that plays in to the calculation is whether the motors are across-the-line started or on some from of speed controller, that affects the starting surge.

All motors are on motor starters, no speed control.

Yes, it will ultimately be up to an engineer or electrician. I want to be able to cite code if at all possible to come out of an existing sub panel. I did not mention the fact all motors will never be on at the same time. The contractor is coming back soon, so I wanted to have this conversation.

I am simply managing this project. The difference of running a 500’ feed vs a 50’ feed is substantial. However, I do know the risks.

 

[zbang]

I don't think you will find something in the NEC for that- it's not a design manual, it's a fire safety code. It really comes down to how many motors you want to run at once and whether the closer panel can supply that load; sometimes people will design specific automation/interlocks to limit the potential draw because the closer source is smaller that optimum. OTOH it may be cheaper to install a longer/larger run than build those interlocks or to suffer an occasional breaker trip (not a good design IMHO).

Look through article 430 for more info about motors, make some operational decisions, then work with the engineer/electrician.

 

[jjwitty]

I don't think you will find something in the NEC for that- it's not a design manual, it's a fire safety code. It really comes down to how many motors you want to run at once and whether the closer panel can supply that load; sometimes people will design specific automation/interlocks to limit the potential draw because the closer source is smaller that optimum. OTOH it may be cheaper to install a longer/larger run than build those interlocks or to suffer an occasional breaker trip (not a good design IMHO).

Look through article 430 for more info about motors, make some operational decisions, then work with the engineer/electrician.

Understood. Thank you.

 

[augie47]

430.24 Exception #3 is a good place to start

Exception No. 3: Where the circuitry is interlocked so as to prevent simultaneous operation of selected motors or other loads, the conductor ampacity shall be permitted to be based on the summation of the currents of the motors and other loads to be operated simultaneously that results in the highest total current.

 

[jjwitty]

430.24 Exception #3 is a good place to start

Exception No. 3: Where the circuitry is interlocked so as to prevent simultaneous operation of selected motors or other loads, the conductor ampacity shall be permitted to be based on the summation of the currents of the motors and other loads to be operated simultaneously that results in the highest total current.

This is exactly what I needed. If we are limited to 80 amps in the subpanel, I could either wire, or program in a way that only allows a max of maybe 4 motors at once.

 

[don_resqcapt19]

Often 220.61 is cited to size a feeder smaller than the total connected load where is it unlikely that the loads will run at the same time.

220.60 Noncoincident Loads
If it is unlikely that two or more noncoincident loads will be in use simultaneously, using only the largest load(s) that will be used at one time for calculating the total load of a feeder or service shall be permitted. If a motor or air-conditioning load is part of the noncoincident load and is not the largest of the noncoincident loads, 125 percent of either the motor load or air-conditioning load, whichever is larger, shall be used in the calculation.