Mohammad Kaiful Wara Khan
New member
- Location
- Saudi Arabia
Why voltage marking on low voltage motors is 460 V and supply voltage is 480 V ?
LV motor supply voltae is 480V, rated voltae is 460V
- Thread starter Mohammad Kaiful Wara Khan
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jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
It is that way for most motors. Supply voltages vary and the motors have to run on voltages that can be less.
This from the NEC:
Table 430.250 Full-Load Current, Three-Phase Alternating-Current Motors
The following values of full-load currents are typical for motors running at speeds usual for belted motors and motors with normal torque
characteristics.
The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440
to 480, and 550 to 600 volts.
This from the NEC:
Table 430.250 Full-Load Current, Three-Phase Alternating-Current Motors
The following values of full-load currents are typical for motors running at speeds usual for belted motors and motors with normal torque
characteristics.
The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440
to 480, and 550 to 600 volts.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Someone, Bob/Iwire, has a good chart on this.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Found it.
- Location
- Massachusetts
That is it! 
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
That is it!
Yep, I had to use google because the search function on here is still a bit funky.
"nominal voltage Iwire holt" pulled it right up.
- Location
- Massachusetts
I don't know why but it looks small in your post.
weressl
Esteemed Member
The data given in the tables by others is useful, but it is helpful to understand the whys.
The generating facilities connect to a wide distribution network. The different supply points on this network continually vary their load. Different loads produce different losses in the distribution network that manifest themselves in different voltage drops on the varying segments of the network.
The the network administrators continually monitor the load and adjust the voltage through various means, but it is of course impossible to assure that voltage with an exact value is available at the use point. Therefore a +/- window was established and the Utility is obliged to keep the voltage within those limits.
The same is true for your own in-facility network and design practice recommends the design of your wire sizes that limits your internal voltage drops to a combined total of 5%. So if you have a 480V transformer, you adjust the tap-changer so that it results in 480V terminal voltage at nominal load, and size your cables that would allow 2% loss to your MCC and a 3% loss from the MCC to the motor.
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