- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Why wouldn't you size the overcurrent protective device based on 430.62 and then add the miscellaneous loads.
Motor feeder calculation
- Thread starter texie
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Read it carefully. It does not say it implies more than one motor. Paraphrased, it says one or more VFD-controlled motor, possibly other motors, and perhaps other loads. Total net minimum one VFD controlled motor. One load does not constitute the need for a feeder... but the conductors can be a feeder all the same.
The 156 (or 155) is already factored 125%. Motor loads are 124A each.
You're elected to write it up.
- Location
- Connecticut
- Occupation
- Engineer
What about It? 430.122 has no mention of the other loads.
Read it carefully. It does not say it implies more than one motor. Paraphrased, it says one or more VFD-controlled motor, possibly other motors, and perhaps other loads. Total net minimum one VFD controlled motor. One load does not constitute the need for a feeder... but the conductors can be a feeder all the same.
The 156 (or 155) is already factored 125%. Motor loads are 124A each.
You're elected to write it up.
I read everything carefully (thoughtfully?)
otherwise why read it
you are seeing something others are not
the sizing imo is the same as multiple motors using vfd rated current rather than motor fla
the vfd 156 is not motor fla x 125%
it is the max input i, it can vary with drive
the 125% is still applied the the vfd input i regardless
After rereading the OP, you are correct in that 156A is the VFD rated input current.
Seems David Luchini sees it as I do.
The power conversion equipment has a combined rated input current of:
156 + 156 = 312A.
Factored:
125% × 312 = 390A
The section doesn't say we have to add other loads, but the feeder circuit conductor ampacity cannot be less than 390A.
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Don't who that is but imo he is wrong
Not accurate
http://www.neca-neis.org/code-question-of-the-day/code-question/cqd-for-3-10-2011
Where multi-motor installations have individual drives, each drive should be sized for the individual motor. The branch circuit conductors supplying the power conversion equipment for the multi-motor power conversion equipment should be sized according to 430.24.
the vfd section only addresses a single motor (re feeders)
for multiple motor ref 430.24
That's one person's opinion. It's not even Charlie Trout answering anymore. He passed back in October 2015.
- Location
- Connecticut
- Occupation
- Engineer
Indeed. I don't understand why you would need to "interpret" what the section says rather than following the plain language of the text.
We don't need anyones 'opinion'
the code is clear
no clarification in X for multiple motors
430.24 applies
1.25 x largest + 1 x sum(others) + 1.25 x misc cont loads
because it only addresses a single vfd
for multiple vfd/motors and other misc loads 430.24 applies since it is not addressed in X
so if a feeder supplies 2 1 hp drives and a 10 kw heater only the vfds need considered when sizing?
more proof that 430.24 applies
kwired
Electron manager
- Location
- NE Nebraska
It isn't supplied by an adjustable speed drive but the feeder in question is still supplying 53 amps of additional unspecified load.
- Location
- Connecticut
- Occupation
- Engineer
Calculate the minimum feeder ampacity from 430.24, then calculate the minimum feeder ampacity from 430.122.
The larger value is your minimum feeder ampacity.
- Location
- Connecticut
- Occupation
- Engineer
It addresses "power conversion equipment." For a feeder, this may be a single vfd or it may be multiple vfd's.
See post #5
Where one or more VFD's are involved, compliance with both 430.24 and 430.122 are required... not one or the other. You cannot ignore 430.122 simply because a branch or feeder circuit supplies more than one VFD... at least not how it is currently worded. If you believe, for multi-motor, multi-VFD applications, ampacity should be determined using 125% of the greater of the largest motor or VFD input current rating according to 430.24, then, by all means, propose it for the next iteration of Code.
- Location
- Connecticut
- Occupation
- Engineer
:thumbsup:
wrong
122 tells you how to size the conductor for a single conversion device (as opposed to conventional starting methods and 1 motor), use the input I rating
24 tells you how to deal with multiple devices (motors, vfd's and misc other loads)
I don't need to propose it, that is already code
- Location
- Connecticut
- Occupation
- Engineer
Wrong.
122 tells you how to size conductors supplying "power conversion equipment." Nowhere does it state that it applies to conductors for a single conversion device.
I disagree
calculate the largest motor or vfd load using motor table fla (430.22) or vfd I input (430.122)
then use 430.24 to calc the total
wrong
it is the equivalent of 430.22 for power conversion equipment 430.122
not for multiple devices, that is 430.24 (which is NOT modified by part X)
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