Please quit telling people to oversize ocpd on AC branch and feeder circuits

Status
Not open for further replies.
infinity said:
10 people have told you that you're incorrect and provided various code articles that you're simply not understanding.
Click to expand...

I will mention that these responders are electrical inspectors, electrical engineers, electricians that work in motor shops, electricians with many years in the trade, long time electrical contractors and all of them very interested and knowledgable in the NEC.

It is not like you are asking random people at the bus station. :)
 
Pharon said:
430.31 tells you how to size for overload and 430.52(B) tells you that you need to size your short circuit and ground fault need to be sized to handle the STARTING CURRENT of the motor (i.e. the LRA).
Click to expand...

430.52 says the branch circuit also needs to be sized for your starting current.
(B) All Motors. The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor.





430.225 Motor-Circuit Overcurrent Protection .225 Motor-Circuit Overcurrent Protection.
(A) General. Each motor circuit shall include coordinated protection to automatically interrupt overload and fault currents in the motor, the motor-circuit conductors, and the motor control apparatus.

430.225 also specifies that the ocpd within the motor is not the primary method of ocp within the motor circuit
 
Yelram said:
430.52 says the branch circuit also needs to be sized for your starting current.
(B) All Motors. The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor.





430.225 Motor-Circuit Overcurrent Protection .225 Motor-Circuit Overcurrent Protection.
(A) General. Each motor circuit shall include coordinated protection to automatically interrupt overload and fault currents in the motor, the motor-circuit conductors, and the motor control apparatus.

430.225 also specifies that the ocpd within the motor is not the primary method of ocp within the motor circuit
Click to expand...

Your point ?
 
Yelram said:
430.52 says the branch circuit also needs to be sized for your starting current.
(B) All Motors. The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor.





430.225 Motor-Circuit Overcurrent Protection .225 Motor-Circuit Overcurrent Protection.
(A) General. Each motor circuit shall include coordinated protection to automatically interrupt overload and fault currents in the motor, the motor-circuit conductors, and the motor control apparatus.

430.225 also specifies that the ocpd within the motor is not the primary method of ocp within the motor circuit
Click to expand...

1. Your first quote sets a minimum for the OCPD, not a maximum. And that minimum is larger than the MCA! The part you quoted says nothing about the conductor size. You have shot yourself in the foot here.
2. The motor overload, set based on the FLA, and the higher amperage short circuit and ground fault protection breaker together form the coordinated protection that the section refers to. This does not support your position either.
 
Have fun explaining that to a judge. "Well Mike Holt told me!" Ill stick with using the ampacity to size the wire, and the wire to size the breaker. Weve been doing it that way since 1975. Never had a unit kick the breaker on startup unless the compressor was grounded.
 
The code actually says that it shall be sized to the name plate rating. Where I've seen the mistake made is EC's adding the 125% to the nameplate rating. That's calculation has already been made on the name plate.

If this answer has already been given, I apologize as I did not read the whole thread.
 
Yelram said:
Have fun explaining that to a judge. "Well Mike Holt told me!"
Click to expand...

That would not be my defense.

My defense would be the words contained in the NEC.

Ill stick with using the ampacity to size the wire, and the wire to size the breaker. Weve been doing it that way since 1975.
Click to expand...

You are free to do that but I hope you have learned doing it the other way is legal, safe and common.
 
Yelram said:
Have fun explaining that to a judge. "Well Mike Holt told me!" Ill stick with using the ampacity to size the wire, and the wire to size the breaker. Weve been doing it that way since 1975. Never had a unit kick the breaker on startup unless the compressor was grounded.
Click to expand...
We will not interfere in any way with your right to use a larger wire than necessary and cost the owner more than necessary. That is between you and your customer. Just do not assert that the NEC makes you do it.
As a practical matter, the smaller conductors should not interfere with proper starting, unless they are so long that a voltage drop calculation would have called for larger wire anyway.
And as a practical matter, your favorite installation is probably just a bit safer, but anybody can do things that are safer then code minimum if they are willing to pay the price.
 
iwire said:
I will mention that these responders are electrical inspectors, electrical engineers, electricians that work in motor shops, electricians with many years in the trade, long time electrical contractors and all of them very interested and knowledgable in the NEC.

It is not like you are asking random people at the bus station. :)
Click to expand...
And just to be fair, there are a LOT of electricians out there that don't get this either.
 
I am reminded of the adage: "Don't confuse me with the facts, my mind is made up" and so be it.
As noted, you are welcome to perform your installations in the manner you see fit. There is certainly nothing unsafe in your following the path you describe.
Some very intelligent folks have pointed out the fallacy in your approach and you choose to ignore what has been pointed out.
I see little need in continuing the discussion.
Your participation in the Forum is appreciated and we look forward to you posting and reading what others contribute but as far as this topic is concerned I am closing the thread rather than continuing the 'argument' further.
 
Status
Not open for further replies.
Top