Voltage Drop

[journeyman0217]

I am wiring a detach garage for a dwelling unit that will have a separate 200 amp service ran to it. The total length of the service line from the utility transformer transformer to the meter is 375'. When I am doing my voltage drop calculation, am I basing my amperage on the service size or can I base it on the "connected load".

 

[infinity]

Voltage drop compensation for this type of installation is optional so it's up to you to decide what you want to calculate for. If you want to ensure that in the future a maximum possible load will not cause a VD below recommended levels then use that number. Otherwise you can use the calculated load but again neither method is required by the NEC. The last option would be to use a number in the middle of the two.

 

[zbang]

I am wiring a detach garage for a dwelling unit that will have a separate 200 amp service ran to it. The total length of the service line from the utility transformer transformer to the meter is 375'.

(underground or overhead?)
Are you supplying/installing this wire or is the utility? If it's the utility, they're probably use whatever they have on the truck.

 

[journeyman0217]

Thank you

 

[journeyman0217]

(underground or overhead?)
Are you supplying/installing this wire or is the utility? If it's the utility, they're probably use whatever they have on the truck.

it is underground, I have to supply it

 

[journeyman0217]

when calculating the voltage drop on a 3 wire 120/240 service, would the voltage be calculated at 240 or 120?

 

[LarryFine]

when calculating the voltage drop on a 3 wire 120/240 service, would the voltage be calculated at 240 or 120?

240v. Treat the total as if the current on the line with the greater 120v load is also on the other line.

For example, if you have 40a of 240v load, 30a of 120v load on one line, and 20a of 120v load on the other line, use (40 + 30) 70a at 240v as your total load.

 

[GoldDigger]

Notice that with the voltage drop on one wire (assuming balanced loads leaving no neutral current) at 120V or the voltage drop on two wires at 240V the calculated percentage VD will be the same.