I am building a pole barn about 225 feet from my house. I need 100 amps 220v out there for the equipment. I was hoping to use direct burial aluminum. It will be connected to the 200 amp disconnect on the outside of my house.

Thank you for your help... Steve

Steve, do you have a question about this? :confused:

Thanks for answering stanfortyman(great quote).
I was looking for a general discussion of problems running long distances with wire, voltage drops or any other problems and their affects on motors, computers, etc.
I also wanted to know exactly what to ask for at the electrical supply house. I have heard the term "trailer wire". I believe it refers to 100 amp direct burial aluminun wire. Also why do you have to run 4 strands why not just 2 hots, neutral and connect the ground to a grounding rod( at one time it seems people would just run 2 hots and earth ground it at its destination). Thanks again, Steve.

Steve. Although you need a separate grounding rod at the shop, you need to run a ground wire from the source panel. The neutral and the ground at your sub panel (shop) need to be isolated. And your right, many people just run the three wires, and it's not acceptable.

Steve. Although you need a seperate grounding rod at the shop, you need to run a ground wire from the source panel. The neutral and the ground at your sub panel (shop) need to be isolated. And your right, many people just run the three wires, and it's not acceptable.
Actually it still is acceptable under the 2005 NEC and earlier, or if local codes allow it. There are some stipulations in using this type of remote feeder, but when done right it is compliant.

Most just use a 4-wire feeder anyway as it avoids any present or future issues.

Thanks guys.. Also I have a 15 hp 3 phase motor and a baldor 3 phase rotary converter. The motor is on a 37 inch wide belt sander. Does anyone know the 220 single phase amperage needed to start the sander?
Thanks again Steve

You say that this will be connected to the 200-Amp main on the outside of your house. How? You cannot connect it to the line side of the main. You also can't connect it to the load side of the disconnect for several reasons. 1) You would not have the proper protection for the wire; 2) The lugs at the main are most likely not rated for multiple conductors; 3) If the supply neutral does not terminate in the main, you would have to run a wire inside of your house (unless the neutral is bare at the main disconnect); 4) You need to tie down the ground wire to the system neutral, requiring another connection to the system neutral.

You do need to run a fourth wire to the sub-panel and ground the sub-panel with a ground rod.

Regarding your sander: There should be a nomenclature plate on the motor or sander, stating the locked rotor current of the motor. While this is not always 100% accurate in every instance, it's a good place to start. I have not done motor calculations for decades, but the running current looks to me to be somewhere in the 30's of amperes. I could be wrong - I can't find my engineering book on motors.

The voltage calculation is easy: 2 x Length x current x resistance of the wire, divided by 1000. The Code allows a maximum of 5% voltage drop from head end to the farthest outlet on the circuit. If you can't hit 5%, you need larger wire.

Finally, you need to pull a permit to do the work. I don't believe that any building inspector would go along with this design.

Y3) If the supply neutral does not terminate in the main, you would have to run a wire inside of your house (unless the neutral is bare at the main disconnect); 4) You need to tie down the ground wire to the system neutral, requiring another connection to the system neutral.
I think I know what you are trying to say here but I am not sure what this means.





You do need to run a fourth wire to the sub-panel and ground the sub-panel with a ground rod.
Again, he definitely should run a 4-wire feeder, but it may not be 100% required.
I suggest looking at the 2005 (or earlier section) 250.32(B)(2)

He would still need overcurrent protection for the feeder at the main. He cannot simply tap off the meter or main disconnect as you correctly state.



The voltage calculation is easy: 2 x Length x current x resistance of the wire, divided by 1000. The Code allows a maximum of 5% voltage drop from head end to the farthest outlet on the circuit. If you can't hit 5%, you need larger wire.
Voltage drop is an NEC FPN suggestion, not a code requirement.

A minor clarification on this statement:


The voltage calculation is easy: 2 x Length x current x resistance of the wire, divided by 1000.

The value of resistance inserted here with the formula as expressed should be the ohms per 1000 feet, thus resulting in dividing by 1000 as expressed by the formula. If the ohms for one foot of wire is used, then dividing by 1000 would not be necessary.

Back to the motor:

Thanks guys.. Also I have a 15 hp 3 phase motor

While a motor should have a nameplate, other than the voltage and horsepower, the running load on the nameplate is not to be used to size anything other than overload protection device.

The tables in Article 430 shall be used to size everything else, such as circuit breaker or fuse, wire size, disconnect size, and controller size.

Table 430.150 Full Load Current,Three Phase AC motors, does not list 220 volts, ( as this is not a standard USA voltage) but can use the 240 volt column, that lists the running load of 42 Amps for a 15 HP 3 phase motor.

Generally speaking, the wire size should be 125% of RLA, 42 * 1.25=52.5 amps, so a #6 minimum is needed for branch circuit. Table 430.52 shows that a circuit breaker can be 250% of RLA, so 42 * 2.5 = max CB allowed will be 105 Amps.

One other thing that must be calculated is the size of the rotary converter. Often this is a single phase motor that will draw current in addition to the current drawn by the three phase motor.

The datasheet and manufacturer instruction of the converter must be reviewed to size this entire motor circuit. This load along with the 3 phase motor load can be a sizable starting load, that can be affected greatly by voltage drop. If the locked rotor amps is not shown on the nameplate, there should be a Code Letter, and there is another table in Art 430 that will list the locked rotor amps, that can be used to size the wire for voltage drop.

Before any sizing of wire is done, we must know all the info on the 3 phase motor, accurately, and all the data on the rotary converter. Voltage drop due to large starting loads of motors is damaging to motors.

Between how I think you were planning on connecting to the main, the distance and voltage drop issue, 3 phase rotary converter, whether a 3 wire feeder is allowed or 4 wire feeder is required, (which code is your area following), your using 220 volts when there is no 220 volts in the USA, you got your hands full, and getting all of the proper advice for all the gory details I am sure you don't know about, is difficult to get from a on-line service.

At this point, I, personally feel that I need to recommend that you hire someone to come in and design/build this system, as doing this yourself, I guarantee something will be missed.