multiple motors single circuit overcurrent protection sizing

Status
Not open for further replies.
H

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
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
 
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)
 
hhsting said:
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
Click to expand...
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. .
 
kwired said:
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. .
Click to expand...

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.
 
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.
 
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.
 
augie47 said:
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.
Click to expand...

Exactly what section in nec its not meeting?


Sent from my iPhone using Tapatalk
 
430.32 & 430.52 for start + associated Art 430 details.
You really need to review Art 430 if you want details.
 
augie47 said:
430.32 & 430.52 for start + associated Art 430 details.
You really need to review Art 430 if you want details.
Click to expand...

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???
 
Last edited:
hhsting said:
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
Click to expand...
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.

Sent from my BE2028 using Tapatalk
 
DrSparks said:
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.

Sent from my BE2028 using Tapatalk
Click to expand...

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

When dis overcurrent protection became overload protection???
 
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.
 
augie47 said:
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.
Click to expand...

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?
 
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.
 
augie47 said:
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)
Click to expand...

Control panel I think has overload protection no SCGF protection. So it cant be supplied by one circuit?
 
If that is the way it is designed, yes.
EDIT: Misread your post.. See POst 13
 
Last edited:
Status
Not open for further replies.
Top