If you are looking at a specific motor, the KVA code establishes a range for starting current (via the kva/hp) at rated voltage. Need to scale it proportionally to voltage.
NEMA MG-1 2003:
10.37 CODE LETTERS (FOR LOCKED-ROTOR KVA)
10.37.1 Nameplate Marking
When the nameplate of an alternating-current motor is marked to show the locked-rotor kVA per
horsepower, it shall be marked with the caption “Code” followed by a letter selected from the table in
10.37.2.
Also there's this...
12.35 LOCKED-ROTOR CURRENT OF 3-PHASE 60-HERTZ SMALL AND MEDIUM SQUIRRELCAGE
INDUCTION MOTORS RATED AT 230 VOLTS
12.35.1 60-Hertz Design B, C, and D Motors at 230 Volts
The locked-rotor current of single-speed, 3-phase, constant-speed induction motors rated at 230 volts,
when measured with rated voltage and frequency impressed and with rotor locked, shall not exceed the
values listed on the next page.
and this...
12.35.2 50-Hertz Design B, C, and D Motors at 380 Volts
The locked-rotor current of single-speed, 3-phase, constant-speed induction motors rated at 380 volts,
when measured with rated voltage and frequency impressed and with rotor locked, shall not exceed the
values shown in Table 12-1.
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Thanks for the replies. If a manufacturer qualifies his motor as a Code Letter B motor (say), while testing the motor, is there a specific tolerance that needs to be observed? Or is it the range of Starting currents as defined by Code Letter B which suffices?
The code letter gives a maximum kva/hp (from which we can calculate a current).
So if it is called a kva code B, my take is that it should be below the max number for B and above the max number for A.
(By the way, dont' confuse KVA code letter with NEMA design letter).
Again - just my understanding from reading NEMA MG-1 which is not exactly easy reading. If anyone else has any other insights, I'd be interested to hear them.
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The starting code letter definition gives the range the motor has to been within. I never heard of any other interpretation, but it's never been a issue. I always use the worst-case.
