Motor FLA Ratings

T

textmi

Member
Location
California
Occupation
EC
If i have a motor that shows 208-230V/460V 3 phase and the amp rating is only shown as one value, is that amp rating for both 208V and 230V? For example, if the amp shows 50A, should I not operate the motor above 50A regardless of whether I am using 208V or 230V?
 
I am not sure I understand the question. You don't "operate the motor" at or above any value. You attach it to its load, turn it on, and it will draw whatever amps it will draw. The nameplate values (or more appropriately the NEC tables) are to help you decide on wire sizes and breaker ratings.

What I would be wondering is whether the 50 amp value is associated with a 460 volt supply or a supply in the range of 208 to 230 volts.
 
This motor is powering a pump. Some pumps are overloading so amp draw may overload the motor due to the point it operates on the pump curve since the bhp requirements are higher.

While a TAB contractor is balancing a pump, they will try to achieve design flow by ramping up the VFD speed but will watch the amp draw on the motor to make sure it is not operating above nameplate FLA.

In this example, the 50 A is listed under (208-230V). There is another value shown for 460V but our system voltage is 208V.
 
textmi said:
If i have a motor that shows 208-230V/460V 3 phase and the amp rating is only shown as one value, is that amp rating for both 208V and 230V? For example, if the amp shows 50A, should I not operate the motor above 50A regardless of whether I am using 208V or 230V?
Click to expand...

Ahh a "tri-voltage" or "cheater" motor thats 208V utilization voltage, 430.6 says to go by the HP and table 430.250, not the amps on the nameplate to determine the current rating. So how many HP is the motor 15?

A motor really designed for a 208Y/120 nominal system will have a utilization voltage nameplate of 200V indicating it does comply with ANSI C84 utilization voltage range B minimum; 180Y/104V.

When I see a 208-230V/460V nameplate I translate it to 208/416 utilization voltage which equals 220/440 'nominal' system voltage AKA your service voltage used in NEC calcs. Since there are not really allot of 220Y/127 services its a compromise voltage manufacturers use so the motor will 'work' on a 208 system and a 240V system (as well as a 480).
However you got to read the fine pint on 'work' as it cant really handle the full voltage range of 208, it clips out on the low end.
 
Last edited:
textmi said:
While a TAB contractor is balancing a pump, they will try to achieve design flow by ramping up the VFD speed but will watch the amp draw on the motor to make sure it is not operating above nameplate FLA.
Click to expand...

In that case, there should be no problem with the motor with any of the nameplate voltages applied. Assuming it’s VFD compatible.
 
textmi said:
If i have a motor that shows 208-230V/460V 3 phase and the amp rating is only shown as one value, is that amp rating for both 208V and 230V?
Click to expand...
I'm surprised that is only shows a single value because the FLA would be different for the two voltages like below.


2 HP Motor Namp;ate.jpg
 
textmi said:
If i have a motor that shows 208-230V/460V 3 phase and the amp rating is only shown as one value, is that amp rating for both 208V and 230V? For example, if the amp shows 50A, should I not operate the motor above 50A regardless of whether I am using 208V or 230V?
Click to expand...

What does it show for service factor? I seem to remember tri-voltage, 1.15 SF motors that showed 1.0 SF for 208V.
 
retirede said:
What does it show for service factor? I seem to remember tri-voltage, 1.15 SF motors that showed 1.0 SF for 208V.
Click to expand...
Possible.

The example in post 6 shows even higher SFA values than the normal rating though.

I sometimes see something like this (snipped from post 6), but with an actual 208 volt Amp value in the far right box if there is no triple value like further up on this nameplate.
1734208706378.png
 
You must log in or register to reply here.
Top