Wire sze calculations confirmation

[goodoboy]

Hello,

I need to size wire per the attached nameplate.

Can you please confirm 4awg from your calculation? I am using 15amp for the entire unit current draw.

Should I use 15amps per phase or 15 amps for the entire unit?

When the vendor measured the actual current draw per leg, they get 7.3amps.

Thanks

 

[charlie b]

#4 seems way oversized to me. I would probably use a #12, unless there is some aspect of the situation that you have not mentioned. Is the load so far from the source that you have a major concern for voltage drop? If not, then why would you select a wire that can handle as much as 85 amps, when the load only draws 15 amps?

Also, there is no such thing as "amps per phase." Presuming a perfectly balanced load, Phase A will draw 15 amps, Phase B will draw 15 amps, Phase C will draw 15 amps, and the device as a whole will be described as drawing 15 amps.

 

[goodoboy]

#4 seems way oversized to me. I would probably use a #12, unless there is some aspect of the situation that you have not mentioned. Is the load so far from the source that you have a major concern for voltage drop? If not, then why would you select a wire that can handle as much as 85 amps, when the load only draws 15 amps?

Also, there is no such thing as "amps per phase." Presuming a perfectly balanced load, Phase A will draw 15 amps, Phase B will draw 15 amps, Phase C will draw 15 amps, and the device as a whole will be described as drawing 15 amps.

I apologize, the load is 1500 ft away and I only want 3% voltage drop.

So are we sizing for each phase wire size?

Thank you

 

[charlie b]

At 1500 feet, I calculate a 2.5% VD on a 15 amp load using #4 awg copper wire. I am not sure what you mean by sizing for each phase wire size, but you would need to use the same #4 for all three phases. You would also have to use a #4 ground wire (equipment grounding conductor) as well.

 

[goodoboy]

At 1500 feet, I calculate a 2.5% VD on a 15 amp load using #4 awg copper wire. I am not sure what you mean by sizing for each phase wire size, but you would need to use the same #4 for all three phases. You would also have to use a #4 ground wire (equipment grounding conductor) as well.

Thank you very much

I think I am confusing myself with understanding the what is the current draw of the entire unit. And the answer is 15amp per the nameplate.

I was thinking I size my wire for 15* sqrt(3) = 25.95amps

 

[charlie b]

The square root of three comes into play when you are comparing the phase currents to line currents. But that relationship is of academic interest only. The 15 amp value shown on the nameplate is the line current. We don't need to care what currents are flowing internal to the motor windings, nor need we care how the motor's internal windings are connected to each other. You will be feeding this device with 15 amps, and you select the wire size on the basis of 15 amps.

 

[GoldDigger]

The Full Load Amps (FLA) of the compressor motor is 6.4A. The FLA of the fan motor is 2.5A, for a total of 8.9A. That is the amperage you need to use to calculate the running voltage drop.

The starting current could be as high as the Locked Rotor Amps (LRA) of ~50A. So you also need to make sure that the voltage drop at that current will not be so high that the motor will have trouble starting.

The two values of 15A shown are the minimum circuit size and the maximum overcurrent device size, and in the absence of VD concerns would be all that you need to take into consideration.

Tapatalk!

 

[goodoboy]

The square root of three comes into play when you are comparing the phase currents to line currents. But that relationship is of academic interest only. The 15 amp value shown on the nameplate is the line current. We don't need to care what currents are flowing internal to the motor windings, nor need we care how the motor's internal windings are connected to each other. You will be feeding this device with 15 amps, and you select the wire size on the basis of 15 amps.

Thank you,

The vendor measured a phase current of 7.3amps when 480V applied in the shop. However, I sized for 1500 ft VD and 15 amps, and the results are 467V will be the actual voltage at the load.

Did I oversize the wire? Should 15 amps be measured?

Thanks,