Motor Control center

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kbsparky

kbsparky

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Delmarva, USA
I am about to install a feeder circuit for a new motor control box, which controls three(3) single-phase 15 HP motors. The nameplate rating on each motor is 48.4 Amps. These are for a community water pumping station, and at least one of these motors will be operating on a continuous basis. While it is possible that all 3 can operate simultaneously, it is highly unlikely, or would be considered a rare circumstance.

According to table 430-248, a 10 HP single phase motor operating at 230 Volts draws 50 Amps. So, either these are super-efficient motors, or the owner was mis-informed as to the actual HP rating of them.

Table 430-248 does not show anything above 10 HP, so does this mean there is no such thing as a 15 HP single phase motor, or ...?


In trying to calculate the proper feeder size for this scenerio, I come up with the following:

3x48.4 Amps = 145.2 Amps
25% of largest motor = 12.1 Amps
Total calculated required circuit capacity = 157.3 Amps

With this result, I figure we would need to install a 2/0 THHN feeder, protected by an inverse-time circuit breaker whose rating could be up to 400 Amps. (I plan to use a 200 Amp breaker at the onset).

Is there anything I'm missing on this?



Edit to add:

The building is existing, and has a 400 Amp single phase service there.

3 phase service is not available in that area.

These pumps will replace an existing array currently fed with a 125 Amp rated feeder.
 
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kbsparky said:
I am about to install a feeder circuit for a new motor control box, which controls three(3) single-phase 15 HP motors. The nameplate rating on each motor is 48.4 Amps. These are for a community water pumping station, and at least one of these motors will be operating on a continuous basis. While it is possible that all 3 can operate simultaneously, it is highly unlikely, or would be considered a rare circumstance.

According to table 430-248, a 10 HP single phase motor operating at 230 Volts draws 50 Amps. So, either these are super-efficient motors, or the owner was mis-informed as to the actual HP rating of them.

A. I know there is few larger single phase motor have rated more than 10 hp. the last 15 hp motor i did recall it ran near 70 amp range and used 100 amp timedelay fuse

Table 430-248 does not show anything above 10 HP, so does this mean there is no such thing as a 15 HP single phase motor, or ...?

A. that true i did check my NEC code book as well they seems cut off at 10 hp single phase but i know there are few single phase motor is much larger than that i did see 15hp , 20 hp , the last one is 100 Hp [ that is diffrent story about that one ]

In trying to calculate the proper feeder size for this scenerio, I come up with the following:

3x48.4 Amps = 145.2 Amps
25% of largest motor = 12.1 Amps
Total calculated required circuit capacity = 157.3 Amps

With this result, I figure we would need to install a 2/0 THHN feeder, protected by an inverse-time circuit breaker whose rating could be up to 400 Amps. (I plan to use a 200 Amp breaker at the onset).

With the figures you provide on 10 HP single phase motor you are pretty close to the figures but senice you mention that very rare for all three motors will be running at the same time. but IMO i will just figure out the worst case sisuation and keep your mind the starting current is the biggest issuse with single phase motors.



Is there anything I'm missing on this?
Click to expand...


If this will be on 15 HP i will give you a rough estame figures but you may have to take a grain of salt to verify this

3X70= 210 amp *
25% of larger motor 17.5 amps
total sum 227.5 amps

this size you may end up useing 300 or 400 amp service unless if possible the POCO can bring in 3 phase system in then it will make the diffrence there.

* = this is my rough number of amprage of 15 hp motor but you may want to double check with the nameplate on the motor itself.

hope it help ya with some of it

Merci , Marc
 
frenchelectrican said:
... you may want to double check with the nameplate on the motor itself....
Click to expand...

As stipulated in the original post, the nameplates on these motors are 48.4 Amps.

The owner of the park told me they were 15 HP. This is where the numbers don't add up, according to the chart in 430-248.

I probably need to go out there and look at those nameplates again <sigh>.
 
kbsparky said:
Is there anything I'm missing on this?
Click to expand...

IMO yes, there is.

Based on the HP, current and voltage the motors are in fact three phase or the motors are single phase 10 HP.

Check table 430.152 and you will find a 3 phase 15 HP draws;

48.3 amps @ 200 volts

46.2 amps @ 208 volts

42 amps @ 230 volts.

It is imposable for a 15 HP single phase motor running in the 230 volt range to be rated as little as 50 amps.

If you can find a 15 HP single phase 230 volt motor the current rating would have to be about 75 amps.

I know you said 3 phase was not available but some one might have ordered the wrong pumps.

If that turns out to be the case don't forget that some VFDs can be supplied single phase and produce a 3 phase output. I would put on my salesmen hat and try to get the sale of three 15 HP VFDs. $$$
 
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I will definately have to go back out there and look again at those nameplates.

I briefly looked at them and verified the running Amps, but took the owner's word for it as to the horsepower rating.

It should be noted that the existing array that is being replaced has 10 HP motors in it.

SO, either he has 3-phase stuff with 15 HP motors, OR he bought 10's with the assumption that he was getting 15's.

I'll go back out there sometime today, and gather all the information on those motors, and their control center --- stay tuned ....
 
KB
When you go back to the site, bring a camera and take pictures of the label(s), this way you do not have to commit to memory any of the info.

It definitely seems as though some of the info you have now is not correct. If the amps they gave you are correct, then my bet is these are 3 phase motors.
 
iwire said:
IMO yes, there is.

If that turns out to be the case don't forget that some VFDs can be supplied single phase and produce a 3 phase output. I would put on my salesmen hat and try to get the sale of three 15 HP VFDs. $$$
Click to expand...

I believe if your were going that route you would have to get vfd's rated for 30 HP to run a 15 HP load. Had a similiar circumstance with Allen Bradley PF 700 a few months ago.
 
Sparky, is this really a MCC (motor control center)? If so special requirements, see 430.62 (A) exception 2.
 
KBsparky :

Thanks for updating the info with the situation.

Bob,, humm i am glad you caught the error on this figure and i went back and double check with my chart and yeah you are right on three phase motor.

But what other suggest is add VFD and use more common 3 ph motor and the control system be adjustable to the water demand useage i think it will work pretty good but only question i think other person in here did mention MCC that is the other question it will have to follow the NEC 430.62 [ i did not read all of it so i will catch up with this later ]

you can use the exsting 400 amp centre.

I dont know about the exsting starter you have in the place right now but i am sure you will have to upsize the starter anyway.

Merci, Marc
 
They are 7-1/2 HP!

They are 7-1/2 HP!

OK, here's the deal:

The motors are in fact single phase 7.5 HP. I don't know where I got the insane idea that they were 15's.

The nameplate Amps listed on each motor is 48.4 Amps (230 Volts), as originally stipulated. Class "H" (whatever that means).

They are all part of an assembly connected to a control box (motor control center?) which has its own label: 240 Volts; 149.2 Amps Max HP 7.5. It would appear that it has built-in overloads, breakers, relays, and a main disconnect switch.

From this information, I assume that I can install a 150 Amp feeder? #0 THHN?
 
Sparky, it is my opinion you are not dealing with Motor Control Center. It should say so on the enclosure you are dealing with. Buss, ect. Let me know if I am wrong. Having said that follow these NEC guidelines.

Sizing feeder conductors (430.24)

look at the motor data in the motor tables provided in NEC. Take the largest motor amp rating and multiply by 1.25. Then add all the other motor current ratings to that. Plus other misc equip. Conductor size cannot be less than the number you come up with.

Sizing ocpd for feeders (430.62)

Find the largest ocpd for one of the motors in your group. Then add the full-load currents of the other motors in your group. That is the maximum setting or rating for your feeder ocpd.
 
KB, I would say you need to verify if the 149A is for the MOCP. If so, you are right with he 150A breaker and cable. Check to see if the panel you are connecting too, has a main breaker or fuses on it, if so what is the size? That will make it easier for connection. Other wise check and see how it is wired internally (is their a schematic?). I would say each contactor and device is probably fused separately.

All roads lead to success, as long as you can decipher the signs along the way!
 
I looked at it again today, and found a label inside of the enclosure that said something along the lines of "Listed Industrial Control Panel" -- IOW, a motor control center as I previously thought.

It would appear that the Code has a new section in it, Article 409 Industrial Control Panels.

Am I required to install anything larger than what would be needed to operate what the nameplate says? [409.110(2)]

Keep in mind that this whole setup is pre-assembled, and wired. Complete with instantaneous breakers, control relays, a main disconnect/breaker, etc. The rating on the "main" is 125 Amps.

The only thing I have to install here is the feeder circuit to the control box.

I'm still leaning towards using #0 THHN conductors on this project.
 
In one of your previous posts you said it was rated or 149A, but if the main is only rated for 125A, then it would not be appropriate to provide anything more then a 125A feeder.

As fas the "Class H", that would be for the temperature rating of the motor insulation. If it is "Code H", that would be related to Table 430.7(B).
 
kingpb said:
In one of your previous posts you said it was rated or 149A, but if the main is only rated for 125A, then it would not be appropriate to provide anything more then a 125A feeder.
Click to expand...


If the control panel has a main, why would it make any difference what size the feeder is, as long as it complies with 430.24 and has overload protection at it's source?

Just curious
steve
 
I'm not sure it falls under 430, it is a feeder and would be in 215. Nevertheless, I guess you could go with 150A feeder, but why spend the extra money when all you can use is 125A.
 
Here lies the dilemma. The nameplate on the control center box states 149 Amps. The built-in main breaker is rated for 125 Amps.

I installed a 150 Amp feeder in any case, job is done now.
 
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