430.24 & 240.4
- Thread starter m sleem
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jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
I am a bit confused by your question.
430.24 is for conductor sizing and it does not state that overload protection is not required.
430.24 is for conductor sizing and it does not state that overload protection is not required.
E.g. two motors 50 flc & 100 flc respectively
The feeder ampacity for this group=1.25x100+50=175a
The OCPD=2.5x100+50=300a
How is the feeder protected by the OCPD?!!!
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- Placerville, CA, USA
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- Retired PV System Designer
Just as for a single motor circuit with a fused disconnect or breaker, the upstream OCPD protects against short circuits and will open under a short before the conductors are damaged.
And the overloads at each motor, either internal or external, will also protect the wires against an overcurrent caused by a failed or overloaded motor.
Tapatalk...
And the overloads at each motor, either internal or external, will also protect the wires against an overcurrent caused by a failed or overloaded motor.
Tapatalk...
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
Yep, and to add: a short circuit or ground fault is just an extreme overload.
Does it mean the motor overload would protect the feeder? what about the unusual overloads at the feeder independently from the motor branch overload?
Non-motor loads are normally fed by tap conductors which are protected by 240.24. Admittedly this does not necessarily protect the main feeder but the "oversized" overcurrent device is a necessary evil to compensate for motor start-up. Chances are if the feeder is overloaded, when the motor starts you may still have a breaker trip.
This is not much different than a MLO service panel where the sum of the breakers often exceeds the service conductor ampacity.
Hopefully in most motor situations, personnel adding loads are qualified enough to take the feeder ampacity into account.
This is not much different than a MLO service panel where the sum of the breakers often exceeds the service conductor ampacity.
Hopefully in most motor situations, personnel adding loads are qualified enough to take the feeder ampacity into account.
- Location
- Illinois
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- retired electrician
You can put the "overload" protection at any point in the circuit and it will provide the "overload" protection for that circuit. The ground fault and short circuit protective device must be at the supply end of the circuit.
I don't know what "unusual" overload conditions you are talking about, can you give an example.
E.g. loosing part of the insulation while installation or maintainance.
Or, adding additional cables in one cable tray leading to increased required ampacity.
petersonra
Senior Member
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- Northern illinois
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- engineer
The required ampacity determines how big the conductors are. if that increases, you have to increase the conductor size. there is no way around that.
Ultimately, most of the faults are mistakes by others & our duty how to avoid it.
petersonra
Senior Member
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- Northern illinois
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- engineer
I do not know what this comment means. perhaps you can elaborate.
- Location
- Illinois
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- retired electrician
That would be a short circuit and or ground fault not an overload.
The fact that you are talking about a motor circuit does not make any difference. If you do something after the fact that changes the ampacity of the conductors, will have to change the size of the conductors or the rating of the OCPD.
- Location
- Illinois
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- retired electrician
That has nothing to do with the sizing of the OCPD. It has everything to do with the selection of the wiring method and the installation practices.
Don, all of the above posts just to ask how we can protect the feeder against overloads in group of motor combination.
The fact is if we can select between either cable damage or breaker trip of course, we will go for breaker trip.
- Location
- Illinois
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- retired electrician
Please read the post that I replied to. It does not appear to me to be to be talking about protection from overloads. The code is clear on how you provide that protection. As others have said the code is the minimum and if you want to exceed the code you are free to do so.
- Location
- Illinois
- Occupation
- retired electrician
Compliance with the code rules provides the required protection.
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