Pumps breaker sizing

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hhsting

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I have domestic water booster pump 480V, 3 phase with (3) 15HP motors being fed by single breaker circuit A.

The circuit A feeds control panel which has fuses for each (3) 15HP motors.

I am thinking circuit A is feeder and breaker should be sized based on 430.62(A) however fuse size inside control panel are not know until the control panel actually gets built. The submittal does not have fuse size

So I have fla of 15hp at 480V is 21A. I can use table 430.52 to size that breaker:

(21x1.75 + 21 + 21) = 78.75A

So then am I correct or incorrect feeder breaker size should be 70A?


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had similar post earlier but was not sure if control panel had any fuses or not.
 
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You would legal with an 80. From personal experience I would use a 100a thermal mag breaker minimum.

It depends on the control scheme of the starters and what style starter is being used. Some of those pumps will hit 3-4x on startup easy.


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I don’t have my code book in front of me right now, but it is 125% of largest motor plus 100% of each additional motor to size the circuit.

However that is the minimum. With across the line starters I always try to bump up the feeder. Especially in some of these well/pump house where it is only supplied by a thermal breaker which tend to trip fairly quick when responding to motor loads.


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ElectricMatt said:
I don’t have my code book in front of me right now, but it is 125% of largest motor plus 100% of each additional motor to size the circuit.

However that is the minimum. With across the line starters I always try to bump up the feeder. Especially in some of these well/pump house where it is only supplied by a thermal breaker which tend to trip fairly quick when responding to motor loads.


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That is for feeder conductor sizing Not for feeder breaker sizing post #1 question
 
Yes that is for your conductors and is sufficient for the minimum legal breaker/fuse size. You can size a breaker up to 200% fla and higher in certain situations.

Breakers/fuses are for GF/SC protection only. With the calculation I provided in the previous post you could go up to a 150a breaker on that circuit legally.
As long as you have overload protection(which you should).


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ElectricMatt said:
Yes that is for your conductors and is sufficient for the minimum legal breaker/fuse size. You can size a breaker up to 200% fla and higher in certain situations.

Breakers/fuses are for GF/SC protection only. With the calculation I provided in the previous post you could go up to a 150a breaker on that circuit legally.
As long as you have overload protection(which you should).


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Designer says fuses in control panel are overload for each pump. 430.62(A) says to get setting of largest branch circuit short circuit protection and plus add all FLA motors.

So if largest branch short circuit protection size is fuse in control panel then largest should be 175% for fuse table 430.52. How can u use 200%? Also 430.52 and can be used only if it is hermatic motors according to 430.62(A) not for booster pumps?
 
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If you are doing plans review, the designer should provide you with the feeder information.
You are misreading 430.62 in regard to hermetic compressors. 430.52 & 430.62 DO APPLY to fixed motor loads.
 
augie47 said:
If you are doing plans review, the designer should provide you with the feeder information.
You are misreading 430.62 in regard to hermetic compressors. 430.52 & 430.62 DO APPLY to fixed motor loads.
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Feeder size can be calculated that is not a problem but maximum feeder breaker size is the question. Please see post #1. I dont see how 430.52 would apply? Their is something in Section 409 but that says if overcurrent protection device is not provided then use 430.50. However control panel has fuses but sizes are not know
 
Art 409 is likely the applicable Article and the info would come from the designer/engineer/manufacturer.
Without input you do not know how many pumps can run simultaneously; In addition, you don't know if a breaker is an acceptable feeder protection method or will fuse protection be required, etc,
Without that, best you can do is a "guesstimate" using 430,62 and 430.52.
You can submit an RFI to the engineer/designer or let the AHJ./inspector check it in the field.
No definite answer can be given here with the limited info. A decent guess would be a 90 amp breaker max.
 
augie47 said:
Art 409 is likely the applicable Article and the info would come from the designer/engineer/manufacturer.
Without input you do not know how many pumps can run simultaneously; In addition, you don't know if a breaker is an acceptable feeder protection method or will fuse protection be required, etc,
Without that, best you can do is a "guesstimate" using 430,62 and 430.52.
You can submit an RFI to the engineer/designer or let the AHJ./inspector check it in the field.
No definite answer can be given here with the limited info. A decent guess would be a 90 amp breaker max.
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Probably i can get how many pumps would be running simultaneously but the info I dont have is fuse size or rating for each branch circuit protection of each pump in Control Panel.

The designer is providing breaker that feeds the control panel which then feeds three pumps.

NEC 2017 section 409.21(C) says to add the largest rating or setting of branch short circuit protection with full load currents of rest of the motors. At the end it says you all use 430.52 and 430.53 if No branch short circuit is provided with industrial control panel.


In my case control panel has branch short circuit protect those are fuse but its rating is not know so how can I even use 430.52 and 430.53? Also how dont see why number of pump running simultaneously is needed?
 
If that doesn’t answer it for your, get the rating of the breaker from the designer/engineer and use 430.53 to get your answer

As Augie said, more information is needed to answer this question. If you asked us to tell you how to design it there are several people on this site that can help you, if you provide all the necessary information.

However, none of us can guess what the engineer will come up with. You are limited by his information, and need to design your feeder around that.


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There are a couple of people far more qualified than me to answer. They are @Jaref ; @Paulenger ;

I have been listening to these two for several years now. They are very intelligent and well versed in this area.

If you listen to the two of them, you can gain a lot of knowledge.


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ElectricMatt said:
If that doesn’t answer it for your, get the rating of the breaker from the designer/engineer and use 430.53 to get your answer

As Augie said, more information is needed to answer this question. If you asked us to tell you how to design it there are several people on this site that can help you, if you provide all the necessary information.

However, none of us can guess what the engineer will come up with. You are limited by his information, and need to design your feeder around that.


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I dont know how 450.53 has to do with anything. See attach Riser left side which code section to size “How to size ” breaker. This is feeder breaker no? The control panel internal to right. Fuse size is unknown. Your part V 430.62(A) says use 430.52 or 440.22(A) for hermetic motors only Not for booster pump.

a83a842bd334e17b6f43ae3398c93f25.jpg
 
Step one: I said nothing about 450.53( a section that does not even exist).

Step 2: I do not know where you got that 430.53 only applies to hermetic compressors. Maybe I missed something.


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ElectricMatt said:
Step one: I said nothing about 450.53( a section that does not even exist).

Step 2: I do not know where you got that 430.53 only applies to hermetic compressors. Maybe I missed something.


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hhsting said:
I dont know how 450.53 has to do with anything. See attach Riser left side which code section to size “How to size ” breaker. This is feeder breaker no? The control panel internal to right. Fuse size is unknown. Your part V 430.62(A) says use 430.52 or 440.22(A) for hermetic motors only Not for booster pump.

a83a842bd334e17b6f43ae3398c93f25.jpg
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In the above hhsting post replace 450.53 with 430.53.

See 430.62(A) in brackets says hermetic motors
 
You said the designer is providing a breaker that feeds the pumps. So you can base your answer off of that breaker size.

There is multiple answers for how to size your breaker for a multi motor feeder. There is different criteria in the selection which falls under the design of the circuit.

So if your looking to design a feeder for the 3 pumps you listed than I will stick with the answer I have given previously.

If you are trying to size your feeder off an assumption than you can start with 430.62(A), this is validated by 430.63(3)

If you need more specific information or are having trouble understanding the code book please specify that and many on here will be glad to help with that.


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