JovialBulge
Member
- Location
- New England
- Occupation
- Programmer
I am trying to size a main panel disconnect and have come up with a few different numbers here and was hoping to gain some clarity on here.
From the UL508a documentation:
30.2.2 A molded-case switch, a switch unit, a fused power circuit switch, a pullout switch, and an open or enclosed switch shall have:
c) For one or more motors or for one motor and any other load(s), an ampere rating or a horsepower rating with an equivalent full-load current:
1) Not less that 115% of the full load current ratings of all motors, in accordance with Table 50.1 or the input current rating of a variable speed drive plus the full-load currents or all other loads; and
2) The rated locked-rotor current of the switch shall not be less than the sum of the locked-rotor currents of all motors, plus the full-load currents of all other loads. For single-phase motors, the locked rotor current is 6 times the full load current rating as in Table 50.1. For three-phase motors, the locked rotor current is as in Table 50.3 for motor designs B, C and D, and 6 times the full load current rating as in Table 50.1 for other motor designs or motors without a motor design designation. For dc motors the locked rotor current is 10 times the full load current rating as in Table 50.2.
So I have:
Motor 1 / 1HP / nameplate FLA is 1.15 / UL508a Table 50.1 FLA is 1.7 / VFD controlling that motor is 2.3
Motor 2 / .75HP / nameplate FLA is NA / UL508a Table 50.1 FLA is 1.3 / VFD controlling that motor is 2.3
Motor 3 / .125HP / nameplate FLA is 0.33 / UL508a Table 50.1 FLA is NA (so i used the next highest size ) 0.9 / VFD controlling that motor is 1.2
Motor 4 / 7.5HP / nameplate FLA is 8 / UL508a Table 50.1 FLA is 9.0 / VFD controlling that motor is 11.2
Motor 5 / 15HP / nameplate FLA is 19 / UL508a Table 50.1 FLA is 17 / VFD controlling that motor is 24.0
Control Transformer is 600VAC to 120VAC / 2,000VA / 3.333A FLA on the line side
So regarding the main disconnect calculation, should it be the FLA on the motor nameplates plus the FLA of the transformer + 115%? It seems to me based on C) 1) above that the motor nameplate FLA is irrelevant and they would prefer you to use the values from Table 50.1. But then again in C) 1) it seems as if the motor is being controlled by a VFD then you would use the VFD's FLA on the line side for the calculation.
From the UL508a documentation:
30.2.2 A molded-case switch, a switch unit, a fused power circuit switch, a pullout switch, and an open or enclosed switch shall have:
c) For one or more motors or for one motor and any other load(s), an ampere rating or a horsepower rating with an equivalent full-load current:
1) Not less that 115% of the full load current ratings of all motors, in accordance with Table 50.1 or the input current rating of a variable speed drive plus the full-load currents or all other loads; and
2) The rated locked-rotor current of the switch shall not be less than the sum of the locked-rotor currents of all motors, plus the full-load currents of all other loads. For single-phase motors, the locked rotor current is 6 times the full load current rating as in Table 50.1. For three-phase motors, the locked rotor current is as in Table 50.3 for motor designs B, C and D, and 6 times the full load current rating as in Table 50.1 for other motor designs or motors without a motor design designation. For dc motors the locked rotor current is 10 times the full load current rating as in Table 50.2.
So I have:
Motor 1 / 1HP / nameplate FLA is 1.15 / UL508a Table 50.1 FLA is 1.7 / VFD controlling that motor is 2.3
Motor 2 / .75HP / nameplate FLA is NA / UL508a Table 50.1 FLA is 1.3 / VFD controlling that motor is 2.3
Motor 3 / .125HP / nameplate FLA is 0.33 / UL508a Table 50.1 FLA is NA (so i used the next highest size ) 0.9 / VFD controlling that motor is 1.2
Motor 4 / 7.5HP / nameplate FLA is 8 / UL508a Table 50.1 FLA is 9.0 / VFD controlling that motor is 11.2
Motor 5 / 15HP / nameplate FLA is 19 / UL508a Table 50.1 FLA is 17 / VFD controlling that motor is 24.0
Control Transformer is 600VAC to 120VAC / 2,000VA / 3.333A FLA on the line side
So regarding the main disconnect calculation, should it be the FLA on the motor nameplates plus the FLA of the transformer + 115%? It seems to me based on C) 1) above that the motor nameplate FLA is irrelevant and they would prefer you to use the values from Table 50.1. But then again in C) 1) it seems as if the motor is being controlled by a VFD then you would use the VFD's FLA on the line side for the calculation.