Which current to be used in the Voltage drop equation to determine the voltage drop?

- Thread starter Charz
- Start date

Which current to be used in the Voltage drop equation to determine the voltage drop?

In general using the rated full load current is close enough. But the exact voltage drop depends on the actual current flow.

If you need to be that accurate then you also need to consider things such as the temperature coefficient of resistance of the conductors, the magnetic interaction of the conduit, the actual load on the motor, etc.

But if you are being this detailed, then maybe you also want to look at things like voltage drop during starting, which blows any of the above details out of the water.

Jon

Unless you exceed the assumed voltage drop, and have less than the rated voltage at the motor. Then the current would be higher, and the voltage drop would also be higher. But that can be hard on motors.

But on the flip side, utility voltages always seem like they run a little high. And I think a 1 HP motor is almost never connected to a 1 HP load. So both of those help to reduce the actual current, and the voltage drop.