Motor Nameplate vs NEC Table

D

dvcraven0522

Member
Location
St. Louis, Missouri
Occupation
Engineer
I have a compressor 60HP motor specification sheet that list 460/3/60 FLA = 87.2. NEC table 430.250 list this motor at 77. I understand in most cases NEC FLA current for amperages shall be used for branch-circuit short-circuit protection and ground fault protection, in lieu of nameplate data.

I know there are exceptions and I would thing this would be one. Although I could not find that exact wording in the NEC. Your thoughts are appreciated.

Dan Craven
Kaemmerlen Electric
 
So the specification sheet is higher than the table, is it marked only in amps? yeah I think this was clarified some in the 2023 NEC, when the motor is marked in amps not HP the rating I think you actually use the table backwayds and get a HP rating from the amps have a look at NEC 430.6
 
dvcraven0522 said:
I have a compressor 60HP motor specification sheet that list 460/3/60 FLA = 87.2. NEC table 430.250 list this motor at 77. I understand in most cases NEC FLA current for amperages shall be used for branch-circuit short-circuit protection and ground fault protection, in lieu of nameplate data.

I know there are exceptions and I would thing this would be one. Although I could not find that exact wording in the NEC. Your thoughts are appreciated.

Dan Craven
Kaemmerlen Electric
Click to expand...
Not sure I understand the exact question here? Does 430.6 (A)(1) Exception No. 2 and or Exception No. 3 help with your application?
 
DASKubiak said:
Not sure I understand the exact question here? Does 430.6 (A)(1) Exception No. 2 and or Exception No. 3 help with your application?
Click to expand...
I believe that's what would apply here. Most likely it's a low speed (high pole count) motor. They always show higher FLA than the charts and you would simply use the higher value. Either that, or that is not the MOTOR nameplate, it is the COMPRESSOR ASSEMBLY nameplate, and includes something like a dryer or lube pump in the FLA value, in which case you use Exception 3...
 
Without more actual details, all the responses so far seem plausible possibilities. One thing not mentioned yet is whether that 87.2 A is actual FLA or if it is service factor amps which sometimes will be on data plate/spec sheets.
 
The amp rating on the equipment is just a bit less than what you would get when you run the motor at its 1.15 service factor rating. I am aware of compressor manufacturer's that have done that.
 
don_resqcapt19 said:
The amp rating on the equipment is just a bit less than what you would get when you run the motor at its 1.15 service factor rating. I am aware of compressor manufacturer's that have done that.
Click to expand...
Every piece of equipment I've measured (largely residential, not industrial)
the nameplate is much higher than the actual measured value. I'm not sure why the vendors are so conservative, it's as if they round up to some much higher number just because.
 
brycenesbitt said:
the nameplate is much higher than the actual measured value.
Click to expand...
The name plate of the motor is when the motor is supplying the full rated horse power of the motor....that rarely happens on most equipment. Same with other equipment...the nameplate is worst case. Probably the equipment where the nameplate most closely matches the real world load is electric resistance heating.

The table full load currents are worst case currents to ensure if a motor is replaced the conductors will be of adequate size for the replacement motor. Given the changes in motor efficiency over the years, it is probably time for teh table full load currents to be revised.
 
You must log in or register to reply here.
Top