When can you use nameplate FLA?

kwired

Electron manager
Location
NE Nebraska
If a motor operated appliance lists FLA, you're allowed to use this current and you're not required to get the FLC from the NEC tables right?

So by extension, when a motor or motor appliance only lists HP, then you must use the tables??
If it is a "motor operated appliance" then you should be using art 422, though it may send you to art 430 for certain things.

Standard sized motors that are listed in tables at end of 430 need to use those table values for motor circuit calculations, this partly so that should motor need replaced (with same HP rating) the conductors should already be sufficient size even though the replacement may have some difference in efficiency rating.

If you have a non standard sized motor (not in the tables) I see no choice but to use the motor nameplate rating for motor circuit calculations.

In all cases motor overload protection is based on nameplate ratings, and overload protection may need replaced or readjusted when replacing a motor.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
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Exception No. 3: For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, the motor full-load current marked on the nameplate of the appliance shall be used instead of the horsepower rating on the appliance nameplate to determine the ampacity or rating of the disconnecting means, the branch-circuit conductors, the controller, the branch-circuit short-circuit and ground-fault protection, and any separate overload protection.
Question is what does exception 3 typically apply to?
That exception was added to address appliances such a central vacuum power units, air compressors and others where they use some very creative horsepower ratings for marking purposes.
 

kwired

Electron manager
Location
NE Nebraska
That exception was added to address appliances such a central vacuum power units, air compressors and others where they use some very creative horsepower ratings for marking purposes.
Or IMO, any other situation where a rating that is not in table in NEC is encountered. Those usually are OEM type applications though.

I run into a lot of crop drying fan motors that are single phase rated 12, 12.5 15, 16 Hp.

Used to be most of them were air-over rated on axial fans where the motor is in the airstream, but in more recent years have run into several 16 HP that are driving centrifugal fans and the motor is not in the air stream.

Largest motor in the NEC table for single phase is 10HP.
 

kwired

Electron manager
Location
NE Nebraska
...

However as VFDs are or should be continuous loads (three hours or more) even though output fluctuates in an elevator application it certainly qualifies for the 125% rule for continuous loads. Most VFDs are powered continuously because the precharge circuits are not designed for routine power up. Many times installers on retrofits put the VFD on the output of a starter only to find it burns up frequently. The VFD manufacturers warn about this but the correct installation removes the contactor and powers it directly off the fuse/breaker. The exception is units with built in input contactors,


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Art 100 definition:
Continuous Load.
A load where the maximum current is expected to continue for 3 hours or more.
Just because something is powered continuously doesn't mean it is drawing "continuous load" all the time it is powered.

Certain code sections do state we must treat the particular load that section is about as continuous loads regardless of what kind of cycling you may see in the field. But that is the general way the NEC works, anything with a higher section number can overrule a lower section number for the most part.

I don't know elevator section very well at all and did glance through it. I don't know if an elevator motor is intended to be treated as continuous load or not. I'd guess nature of load would be non continuous, but NEC may still state you need to treat this one as continuous load, especially if it is a motor that is nameplated as a continuous duty motor. If it has any kind of intermittent duty on the nameplate then that is generally what triggers the ability to use conductors and overcurrent protection based on intermittent duty allowances when it comes to motors in general.
 
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