Voltage drop over several buildings

[jimingram]

I am calculating the voltage on several ministorage buildings. There are 12 buildings 80' apart. The load on each building is 28 amps. The service will be located in the first building. The utility transformer is 200' away.

I am planning to split the load between two feeders. Each building will tap the feeder and terminate in a main breaker panel. As the feeder progresses the load decreases. For example at 480 feet the load on the feeder will be 168 amps, at 560' the load will 140 amps, and continuing in this matter until the last building.

I have the formula for calculating voltage drop. However, I am only confident of the calculation from the service to the first building. I'm unsure how to calculate the voltage drop to the next buildings as the load decreases and the length increases. I would assume the wire size could be smaller.

I did a separate calculation for each of the remaining buildings. I used the increased length and decreased load from one building to the next. Calculating this way resulted in a reduction of the wire size to each subsequent building.

Is this a legitimate way of calculating voltage drop over several buildings?

I am hoping to eventually centrally locate the service but for now I have to assume it will be at the first building.

 

[bob]

I am calculating the voltage on several ministorage buildings. There are 12 buildings 80' apart. The load on each building is 28 amps. The service will be located in the first building. The utility transformer is 200' away.

I am planning to split the load between two feeders. Each building will tap the feeder and terminate in a main breaker panel. As the feeder progresses the load decreases. For example at 480 feet the load on the feeder will be 168 amps, at 560' the load will 140 amps, and continuing in this matter until the last building.

I have the formula for calculating voltage drop. However, I am only confident of the calculation from the service to the first building. I'm unsure how to calculate the voltage drop to the next buildings as the load decreases and the length increases. I would assume the wire size could be smaller.

I did a separate calculation for each of the remaining buildings. I used the increased length and decreased load from one building to the next. Calculating this way resulted in a reduction of the wire size to each subsequent building.

Is this a legitimate way of calculating voltage drop over several buildings?

I am hoping to eventually centrally locate the service but for now I have to assume it will be at the first building.

The second caculation is done just as you did the first. You will get the voltage drop in that section of conductor. However, you must add the voltage drop in the first caculation to the second caculation to get the VD at the second building. The next section is done the same way and you add the VD at the second building to get the VD at the third building. The wire size may not be able to decrease. You will not know until you have finished all of the caculations. When you are finished put you number up for review. Someone has a program that will check your results.

 

[dbuckley]

Have a look at this thread which shows how to do it and links to some calculators.