Motor control panel

[jjwitty]

Can somone help me with total OC for a panel for pumps? The panel will be 18 3p 480v motors equal to 188 total FLA. If a panel is non continuous use, does the disconnect equal 175% of FLA? I am not sure if it changes much with the non continuous or not. Add in control voltage I expect FLA to be about 193, so if we have to go 175%, we’re looking at a 400amp feed. Anyway around this ?

 

[infinity]

Are you asking about the feeder size? You mentioned disconnect.

 

[jjwitty]

There will likely need to be a new feed we don’t have be available power anywhere else. The only option we have is installing a new bucket in our MCC.

 

[ptonsparky]

What is 1.25 times the largest plus the remaining? IF they all run but start at separate times.
or
1.25 times the largest load(multiple motors) plus the remaining that will run but start at separate times?

That would be the starting point for me.

 

[BillyMac59]

The non-continuous load means little in sizing the feeder. If its possible to have all motors running at the same time, however briefly, you must size for that. The above post cites 125% of largest load + sum of all other loads. I agree with starting here.

 

[jjwitty]

What is 1.25 times the largest plus the remaining? IF they all run but start at separate times.
or
1.25 times the largest load(multiple motors) plus the remaining that will run but start at separate times?

That would be the starting point for me.

I misspoke on my first post. Disconnect would be 125% of highest plus sum of remaining. I am asking about the feeder circuit that comes from the MCC. I am planning a project that could go 200 amp disconnect at best. At worst we need a new service line ran and that’s what I am afraid will be 175% of FLA or 400amp.

 

[ptonsparky]

Why do you need a 400?
You are not required to put in the max CB. It can be less.

 

[jjwitty]

Why do you need a 400?
You are not required to put in the max CB. It can be less.

Contractor suggested 400 amp feed. I can only find one code where it says 175% for motor inrush. I assume he’s following that since it’s a motor control panel the new service feed will be supplying

 

[PaulEd]

What are the HP of the motors?

 

[jjwitty]

What are the HP of the motors?

9, 15hp and 9, 5hp. Comes out to around 190FLA

 

[kwired]

You have two things to calculate here.

minimum conductor ampacity - which is the already mentioned 125% of largest motor plus all other motors (using nec motor current tables) and can be found in 430.24.

Then there is maximum short circuit/ground fault protection which is covered in 430 part V. If you are supplying motors only then 430.62 is what you are looking for here. If the conductors are minimally sized per 430.24 then maximum protection is largest setting permitted (175% would suggest it is based on time delay fuses in your case) for the largest motor plus the rated current of the remaining motors.

Do not know what your largest motor is, but if sum of all motors is 188 I guess there can be a chance of you getting this under 200 if largest motor isn't too large. If this calculation yields say 250 amps as the largest fuse then you will have to go with 400 amp fuse holder and max of 250 amp fuse, but the conductor can still be whatever 125% of largest motor current is plus all other motors which will be less than 250, depending on largest motor could even be under 225.

Motor overload protection is inherently going to protect these conductors from overloading.

 

[kwired]

9, 15hp and 9, 5hp. Comes out to around 190FLA

1 15 HP @ 125% plus 8 15 HP @ 100% plus 9 5 HP @ 100% is your minimum conductor. Then take the one 15 @ 175% and the rest at 100% is your maximum time delay fuse.

Use table 430.250 for determining motor currents not the motor nameplates.

 

[kwired]

I come up with needing minimum conductor ampacity of 263 amps.

max fuse size of 273, I don't see anything allowing next higher rated OCPD. However 300kcmil copper is good for 285 amps which is above your minimum needed of 263 and can be protected at next higher standard device which is 300 per general overcurrent protection rules since your load is not over 285.

 

[kwired]

My result should be what NEC says is minimum feeder conductor and maximum overcurrent protection should be for this feeder circuit.

Real world tells me that unless these motors are all fully loaded and all run and/or if too many happen to start at same time it has a fairly good chance of operating trip free on a 200 amp feeder circuit.

 

[ptonsparky]

My result should be what NEC says is minimum feeder conductor and maximum overcurrent protection should be for this feeder circuit.

Real world tells me that unless these motors are all fully loaded and all run and/or if too many happen to start at same time it has a fairly good chance of operating trip free on a 200 amp feeder circuit.

Without knowing all those little details, that would be my SEWAG as well.

 

[jjwitty]

Without knowing all those little details, that would be my SEWAG as well.

That’s another issue, these motors will never run at the same time which brings noncoincidental load into question. I am willing to interlock circuit so only x amount of power can be consumed at once.

 

[PaulEd]

That’s another issue, these motors will never run at the same time which brings noncoincidental load into question. I am willing to interlock circuit so only x amount of power can be consumed at once.

What’s your “coincidental load” here? Is one for heating and ones for cooling? As far as I know that’s the only way to use the coincidental loads exception?

 

[ptonsparky]

What’s your “coincidental load” here? Is one for heating and ones for cooling? As far as I know that’s the only way to use the coincidental loads exception?

Interlocking works just fine. We could careless what the other loads are if the can't come on at the same time.

 

[don_resqcapt19]

What’s your “coincidental load” here? Is one for heating and ones for cooling? As far as I know that’s the only way to use the coincidental loads exception?

It is any two loads that are "unlikely" to run at the same time. Note, it only says "unlikely".

It does not require interlocking to prevent the two loads from running 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.

 

[jjwitty]

What’s your “coincidental load” here? Is one for heating and ones for cooling? As far as I know that’s the only way to use the coincidental loads exception?

We have hundreds of pumps in our facility. We have 10 “tank farms” with about 10 pumps each. We don’t have the manpower, or the customer demand to run more than one or two 15hp pumps at once in each tank farm. Most of the time a blender is pumping one product to another tank, when they are complete they shut that pump off and move to the next. What’s more likely is running the 5hp motors because they are used to heat the oil.