480V Power Cable splice down recommendation

[adityalagudu3291]

We are using 3C W/G 500MCM, 2000ft, 480V power cable to feed one of our 100hp pump motors. Around 1800ft of the cable is on pipe rack and the remaining 200ft will be drop down from pipe rack to underground duct bank. UG duct bank will have a 6" conduit.
We want to splice down the cable to 3C, 4/0AWG at the end of the pipe rack, due to space restrictions at the motor junction box. Could we splice down the cable to 4/0, for almost a length of 200ft? Any suggestions on what the code implicates.

 

[kwired]

No reason you can't reduce to 2/0 which off top of my head is minimum size conductor needed for 100 hp @ 480 volts, unless you have voltage drop considerations that tell you otherwise to use something larger.

Seems this would be at least on borderline of consideration to use a higher voltage and less copper, though I don't know how much cost difference would be for some the higher volt conductors and equipment.

 

[adityalagudu3291]

No reason you can't reduce to 2/0 which off top of my head is minimum size conductor needed for 100 hp @ 480 volts, unless you have voltage drop considerations that tell you otherwise to use something larger.

Seems this would be at least on borderline of consideration to use a higher voltage and less copper, though I don't know how much cost difference would be for some the higher volt conductors and equipment.

My question is how do we calculate the voltage drop of a cable when it is splice down. Is it acceptable to use 4/0 cable for a 200ft, in this situation? I believe it will affect the overall voltage drop percentage. Generally, we do splice down of a cable nearby motor termination point.

 

[kwired]

My question is how do we calculate the voltage drop of a cable when it is splice down. Is it acceptable to use 4/0 cable for a 200ft, in this situation? I believe it will affect the overall voltage drop percentage. Generally, we do splice down of a cable nearby motor termination point.

you have two voltage drops to calculate. first one being across 1800 feet of 500 second one being across 200 feet of 4/0 add the two together to get net drop of the entire circuit. Current is same in both sections of the circuit, resistance of each section will be different resulting in different voltage drop across each section, doesn't matter if the 4/0 were at the beginning or the end of the circuit either.

 

[adityalagudu3291]

you have two voltage drops to calculate. first one being across 1800 feet of 500 second one being across 200 feet of 4/0 add the two together to get net drop of the entire circuit. Current is same in both sections of the circuit, resistance of each section will be different resulting in different voltage drop across each section, doesn't matter if the 4/0 were at the beginning or the end of the circuit either.

Okay, understood. Consider adding voltage drop percentage of both 1800ft cable on pipe rack tray and 200ft cable on UG conduit, the VD is less than 5%. So it is feasible.