I would like to run entrance cable from my house to a out building 625' away under ground. What size wire would I need to do this? The building would have a stove, refrigerator, ac window unit, washer dryer, hot water heater. Would prefer to use aluminum wire if possible.

How many AMPS?. without that there is no way of knowing a correct size.

200amps

To illustrate that a large conductor will be needed to run 240 volts 625 feet, let's assume a 30 amp load at 240 volts, using a voltage drop calculator from Southwire arrives at:

1 conductors per phase utilizing a #2/0 Aluminum conductor will limit the voltage drop to 2.55% or less when supplying 30.0 amps for 625 feet on a 240 volt system.
For Engineering Information Only:
135.0 Amps Rated ampacity of selected conductor
0.16 Ohms Resistance (Ohms per 1000 feet)
0.043 Ohms Reactance (Ohms per 1000 feet)
7.199999999999999 volts maximum allowable voltage drop at 3%
6.103. Actual voltage drop loss at 2.55% for the circuit
0.9 Power Factor


Now lets assume there is only a 20 Amp load at 120 volts:

1 conductors per phase utilizing a #3/0 Aluminum conductor will limit the voltage drop to 2.82% or less when supplying 20.0 amps for 625 feet on a 120 volt system.
For Engineering Information Only:
155.0 Amps Rated ampacity of selected conductor
0.13 Ohms Resistance (Ohms per 1000 feet)
0.042 Ohms Reactance (Ohms per 1000 feet)
3.5999999999999996 volts maximum allowable voltage drop at 3%
3.383. Actual voltage drop loss at 2.82% for the circuit
0.9 Power Factor

So, I need to assume the amp load may be a bit higher that my assumptions for illustration purposes, which can be a good possibility.

The water heater alone, assuming a typical 4500 watt unit, will draw 18.75 amps alone. Dryer will be 20.84 amps, range can draw 8000 watts at 33.34 amps.

If all of these are on at the same time, which is very feasible, keep in mind we have no lights, reefer, or AC on yet, total amp load will be 72 amps.

Using 72 amps arrives at:

1 conductors per phase utilizing a #350 Aluminum conductor will limit the voltage drop to 2.89% or less when supplying 72.0 amps for 625 feet on a 240 volt system.
For Engineering Information Only:
250.0 Amps Rated ampacity of selected conductor
0.066 Ohms Resistance (Ohms per 1000 feet)
0.04 Ohms Reactance (Ohms per 1000 feet)
7.199999999999999 volts maximum allowable voltage drop at 3%
6.916. Actual voltage drop loss at 2.89% for the circuit
0.9 Power Factor

So, how badly do you want to run a feeder 625 feet for this outbuilding?

The smaller the wire you use will dictate how much load you can operate at once and have it operate properly.


Motors do not tolerate voltage drop. Reefer and AC motors will try to start, and each starting current will be higher than the running current, and will raise the voltage drop as they are trying to start.

Resistance heat, such as water heater, dryer, and range, will all operate, or seem to, but not get hot enough if the voltage drop is too high.

The calculator is set for 3%, as the recommended maximum vD, is 5% at the device, allowing for 2% for the branch circuit wiring. This is only a design recommendation. Most electric equipment will operate +/- 10%.

The choice is up to you what size wire you would like to run. May be wise to see if the utility can provide power at a shorter distance.