multiple motors single circuit overcurrent protection sizing

[hhsting]

I have three 208V, three phase, 10HP, domestic booster pumps triplex parking basement of high rise building shown in plans.

The booster pump are fed from one circuit breaker in panelboard. The circuit breaker size is 200A.

I am trying to verify the size of the breaker. Where in NEC 2017 section 430 would overcurrent protection for multiple motors fed from one circuit be addressed?


Note: additional question maybe come up depending upon response provided

 

[augie47]

430.25 for the feeder, 430.62 for the feeder OCP device.

(I believe that would be a 125 amp breaker.... If you use the 200 amp breaker, the feeder would need to be rated 200 amp)

 

[kwired]

I have three 208V, three phase, 10HP, domestic booster pumps triplex parking basement of high rise building shown in plans.

The booster pump are fed from one circuit breaker in panelboard. The circuit breaker size is 200A.

I am trying to verify the size of the breaker. Where in NEC 2017 section 430 would overcurrent protection for multiple motors fed from one circuit be addressed?


Note: additional question maybe come up depending upon response provided

Do you have individual branch circuits and asking what size feeder is needed to handle these three motors?

I believe you need minimum feeder conductor ampacity of 91 amps.

As mentioned probably at least 125 amp thermal mag breaker.

Bet many cases a 100 amp breaker will hold though, mostly depends on startup situation

Put them on soft starters or VFD's even an 80 amp breaker holds unless they are fully loaded for extended periods of time. .

 

[hhsting]

Do you have individual branch circuits and asking what size feeder is needed to handle these three motors?

I believe you need minimum feeder conductor ampacity of 91 amps.

As mentioned probably at least 125 amp thermal mag breaker.

Bet many cases a 100 amp breaker will hold though, mostly depends on startup situation

Put them on soft starters or VFD's even an 80 amp breaker holds unless they are fully loaded for extended periods of time. .

I am asking I have one feeder and from that feeder three motors are connected. I do NOT have individual branch circuits to the motors

The feeder breaker to that one feeder is sized 200A.

 

[augie47]

In most cases including this one the individual motors would need to be on their own branch circuits in order to provide proper overload and short circuit protection.

 

[hhsting]

In most cases including this one the individual motors would need to be on their own branch circuits in order to provide proper overload and short circuit protection.

Well if the designer placed 3 motors on one circuit then how can NEC stop it?

 

[augie47]

Hopefully a good plan review would catch it and send it back as not meeting the NEC, a contractor will question it, or a knowledgeable inspector would reject it as not meeting NEC.

If its a decent designer I would say its an oversight or will be corrected when brought to his attention.

 

[hhsting]

Hopefully a good plan review would catch it and send it back as not meeting the NEC, a contractor will question it, or a knowledgeable inspector would reject it as not meeting NEC.

If its a decent designer I would say its an oversight or will be corrected when brought to his attention.

Exactly what section in nec its not meeting?


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[augie47]

430.32 & 430.52 for start + associated Art 430 details.
You really need to review Art 430 if you want details.

 

[hhsting]

430.32 & 430.52 for start + associated Art 430 details.
You really need to review Art 430 if you want details.

Do you mean NEC 2017 section 430.28? If designer provides one feeder then he mist comply with 430.28. Unless if he provides same conductors throughout it wont be a tap???

 

[DrSparks]

I have three 208V, three phase, 10HP, domestic booster pumps triplex parking basement of high rise building shown in plans.

The booster pump are fed from one circuit breaker in panelboard. The circuit breaker size is 200A.

I am trying to verify the size of the breaker. Where in NEC 2017 section 430 would overcurrent protection for multiple motors fed from one circuit be addressed?


Note: additional question maybe come up depending upon response provided

Overcurrent, or rather overload protection for multiple motors really can't be accomplished using a single OCPD unless all of the motors operate continuously or simultaneously. And generally, this would be a very poor design.

Generally, circuit breakers feeding are there only to provide short circuit / ground fault protection. So the rating of the breaker can be much higher than one might expect. Each motor would then have it's own overload protection device, such as a contactor/overload combo unit. See table 430.52.

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[hhsting]

Overcurrent, or rather overload protection for multiple motors really can't be accomplished using a single OCPD unless all of the motors operate continuously or simultaneously. And generally, this would be a very poor design.

Generally, circuit breakers feeding are there only to provide short circuit / ground fault protection. So the rating of the breaker can be much higher than one might expect. Each motor would then have it's own overload protection device, such as a contactor/overload combo unit. See table 430.52.

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Ok so By overcurrent protection I meant short circuit protection NOT overload protection.

When dis overcurrent protection became overload protection???

 

[augie47]

There are, of course, exceptions but generally every motor must have overcurrent (overload) protection per Part III of Art 430 and each motor must have short-circuit groundfault protection per Part IV of Art 430. There are rare conditions where multiple motors, especially larger than 1 hp, don't need this individual protection. Once each has it's indvidula protection, they, as a group, can be suppled by a feeder Per Part II and Part V,
If you want to analyze different scenarios you should get some of Mike's books (CDs) on Art 430.

 

[hhsting]

There are, of course, exceptions but generally every motor must have overcurrent (overload) protection per Part III of Art 430 and each motor must have short-circuit groundfault protection per Part IV of Art 430. There are rare conditions where multiple motors, especially larger than 1 hp, don't need this individual protection. Once each has it's indvidula protection, they, as a group, can be suppled by a feeder Per Part II and Part V,
If you want to analyze different scenarios you should get some of Mike's books (CDs) on Art 430.

So their is control panel for three motors I think so if their is one breaker one circuit to the one disconnect by the controller which feeds the control panel I dont see what is wrong?

 

[augie47]

If the "control panel" provides the proper oveload and SCGF protection for each motor then it would only need a feeder meeting the nameplate requirements of the panel. (likely it would need to need Art 409 and be NRTL)

Hopefully we didn't wait to Post 14 for you to inform that there is a control panel.

 

[hhsting]

If the "control panel" provides the proper oveload and SCGF protection for each motor then it would only need a feeder (likely it would need to need Art 409 and be NRTL)

Control panel I think has overload protection no SCGF protection. So it cant be supplied by one circuit?

 

[augie47]

If that is the way it is designed, yes.
EDIT: Misread your post.. See POst 13

 

[hhsting]

If that is the way it is designed, yes.

This is because of 450.53?

 

[augie47]

Possibly but more likely 430.54 and 430.7(D)

 

[hhsting]

Possibly but more likely 430.54 and 430.7(D)

I dont follow none them say you cannot fed one circuit conductor from one breaker which is SCHF to control panel where control panel only has overload for 3 motors?