Voltage Drop Calc for a 3-phase system

[match0927]

I am using the formulas D=(VD*CM)/(1.732*K*I) to calcualte the maximum distance due to a specific voltage drop for a 1800W electrical equipment 120/208V.
where D is the maximum distance
CM is the circular-mils
K is direct current constant, here using 12.9 for copper wire
I is the load curret

Assuming 2% of votage drop, VD is 208*2%=4.16V
Load current 1800/208/1.732=5A
For #6 AWG, CM=26240
Finally, I got the maximum distance D=977ft
What confusing me is that in the product spec, it only allows 557ft in this case, is that company wrong with this data?

 

[bob]

I am using the formulas D=(VD*CM)/(1.732*K*I) to calcualte the maximum distance due to a specific voltage drop for a 1800W electrical equipment 120/208V.
where D is the maximum distance
CM is the circular-mils
K is direct current constant, here using 12.9 for copper wire
I is the load curret

Assuming 2% of votage drop, VD is 208*2%=4.16V
Load current 1800/208/1.732=5A
For #6 AWG, CM=26240
Finally, I got the maximum distance D=977ft
What confusing me is that in the product spec, it only allows 557ft in this case, is that company wrong with this data?

Your post says "electrical equipment 120/208". That appears to be single phase. You use "Load current 1800/208/1.732=5A" to calculate the current. I can not imagine a 1800 watt device requiring
3 phase. If single phase, the 1.73 is not part of the calculation.

 

[drbond24]

They are probably just using a tighter voltage drop requirement.

Bob does have a point; you should verify if the circuit is 120 single phase, 208 single phase, or 208 three phase. It isn't clear from your post.

Just did a quick calc: if the circuit were 208 single phase with the other data you provided, the voltage drop is right at 4% at 557 feet. Perhaps this is the ceiling the manufacturer was working with.

 

[match0927]

Well, Actually, the 120/208 is a wind turbine. its a three-phase with a neutral line. I think the current should be correct..

Your post says "electrical equipment 120/208". That appears to be single phase. You use "Load current 1800/208/1.732=5A" to calculate the current. I can not imagine a 1800 watt device requiring
3 phase. If single phase, the 1.73 is not part of the calculation.

 

[bob]

Well, Actually, the 120/208 is a wind turbine. its a three-phase with a neutral line. I think the current should be correct..

Well either way the voltage drop is very small. Don't know why the mfg specs
show 577 ft.

 

[kpdci]

Voltage Drop

Voltage Drop

One thing I'm not sure about. Given, voltage drop is caused by resistance. Say for example, at one point in the field, there is 60 feet from a building and a splice is to be done. One direction from the splice, there is 180 feet and the other direction of the splice there is 200 feet. Would the total length for the voltage drop formula be 60 + 180 for one direction or would it be 60 + 180 + 200?

Thanks
Kevin

 

[match0927]

i am not sure if I am right. the total length for the voltage drop formula should be 60+180 for one direction and 60+200 for the other direction.

One thing I'm not sure about. Given, voltage drop is caused by resistance. Say for example, at one point in the field, there is 60 feet from a building and a splice is to be done. One direction from the splice, there is 180 feet and the other direction of the splice there is 200 feet. Would the total length for the voltage drop formula be 60 + 180 for one direction or would it be 60 + 180 + 200?

Thanks
Kevin

 

[bob]

One thing I'm not sure about. Given, voltage drop is caused by resistance. Say for example, at one point in the field, there is 60 feet from a building and a splice is to be done. One direction from the splice, there is 180 feet and the other direction of the splice there is 200 feet. Would the total length for the voltage drop formula be 60 + 180 for one direction or would it be 60 + 180 + 200?

Thanks
Kevin

The caculation should be the total load thru 60 ft. Caculate the load in the 180 ft. Caculate the drop for the load in the 200 ft.
Add the drop in the 60 ft to the drop in the 180 ft. Then add the 60 ft drop to the drop in the 200 ft.