277 vs 480

[Alwayslearningelec]

When determining voltage of a feeder from a 277/480v what determine if the voltage of the feeder is 277v or 480v?

 

[augie47]

If the neutral is present it is a 480/277 feeder. With no neutral it would be a 480 feeder.

 

[xformer]

IMHO... Both. It would be nominal voltage that is used in the system.

 

[Alwayslearningelec]

If you were running voltage drop calc what voltage would you input? 480?

 

[Alwayslearningelec]

On another separate but related note.
When you figuring voltage drop and they tell you they want power for a particular amperage, say 400A would you input that amperage/current or do you technically need to find the calculated load which be more accurate for sizing the proper wire?
Guess you would need to know if the requested amps is the actual load or not?? Thanks.

 

[augie47]

You would use values that address the results desired. IF you want to know the drop for a specific load, use that load; IF you want to know the theoretical circuit full load, use that number.

 

[ggunn]

If you were running voltage drop calc what voltage would you input? 480?

For the balanced case I use Vd = IR = DIr where D = distance in feet, I = current, and r = ohms per 1000'
%Vd = (Vd/V)(100%) where V = 277V
Note the one way distance because in the balanced case the current in the neutral is zero.

 

[LarryFine]

If you must use a single number, be like the POCO and use the higher, i.e. the L-L voltage.

 

[ggunn]

If you must use a single number, be like the POCO and use the higher, i.e. the L-L voltage.

You can but in the calculation there's a factor of sqrt(3) in both the numerator and the denominator. You will end up with the same answer.