# Motor conductor sizing?



## lectric_hand6855 (Jan 24, 2009)

The table flc is the max it can be for any motor (of that type) at that voltage therefore its typically higher, thats why it is used for wire size and ocpd to ensure enough capacity. The nameplate flc is used for overloads in order to keep protection as close as possible to the actual motor's flc. Of course there are exceptions for certain types of motors. Hope this clears things up.


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## Mike in Canada (Jun 27, 2010)

Just to add to what the other poster said, the reason table 44 is used is to make sure that if the motor gets replaced in the future by another motor of the same horsepower the wiring will be able to handle it. So table 44 is sort of a 'worst case scenario' of amperage requirements.

Mike


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## jwjrw (Jan 14, 2010)

The tables are used to size the conductors like the others said. The nameplate is used to size overcurrent protection. You look at the minimum/maximum circuit ampacity to know the minimum size overcurrent protection you are allowed to use.


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## bushwickbill (Jan 17, 2010)

Awesome guys. Thanx for the quick replies. That makes a lot of sense. I feel more confident in my answers now.
Cheers!!


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## Mogie (May 26, 2010)

jwjrw said:


> The tables are used to size the conductors like the others said. The nameplate is used to size overcurrent protection. You look at the minimum/maximum circuit ampacity to know the minimum size overcurrent protection you are allowed to use.


The tables are used to size _both_ conductors and OCPD. The nameplate is used _only_ for sizing overloads.


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## bushwickbill (Jan 17, 2010)

The confusion was when to use or not use the Motor Nameplate FLA? In Canada we use either the Motor nameplate FLA or the table FLA (@125%) to size the conductor.
It seems the NEC only allows you to use the tables when sizing the conductors @125%. The NEC says you cannot use the motor nameplate FLA for that calculation. 
Which I feel makes more sense than our use either the tables or the nameplate FLA for that motor conductor sizing. What if you size the motor conductors based on a very efficient PF motor Nameplate FLA. Then five years later that motor fails, The new motor being installed on those same conductors has a very bad PF, Well, Now those conductors that were based for a more efficient motor might not be sufficient now for the new motors appetite for more AMPS?
But thanx for the clarification guys.


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## jwjrw (Jan 14, 2010)

Mogie said:


> The tables are used to size _both_ conductors and OCPD. The nameplate is used _only_ for sizing overloads.


 
Actually overloads and overcurrent protection are listed on the nameplate. The minimum circuit ampacity on the nameplate IS what you size your overcurrent protection to. I'm sure you have seen "max breaker" listed on a nameplate before.


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## Bob Badger (Apr 19, 2009)

jwjrw said:


> Actually overloads and overcurrent protection are listed on the nameplate. The minimum circuit ampacity on the nameplate IS what you size your overcurrent protection to. I'm sure you have seen "max breaker" listed on a nameplate before.


When dealing with just a motor there will not be any MCA or max breaker listed.

You look at the HP rating and use the tables in 430 to size everything except the overloads. The overloads are sized by the current rating on the motor tag.


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## jwjrw (Jan 14, 2010)

Bob Badger said:


> When dealing with just a motor there will not be any MCA or max breaker listed.
> 
> You look at the HP rating and use the tables in 430 to size everything except the overloads. The overloads are sized by the current rating on the motor tag.


 

Guess I should of actually read the thread before posting:whistling2:
Easy to be wrong when you are talking about one thing and everyone else is talking about something else.


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