# Why is large voltage drop a problem if within nameplate rating on motor?

We are in the process of trying to find out why 1/0 AL wire over 400' of length to supply a 2HP motor for a Bifold Door is being pushed so hard by door manufacturer.

We have a door on order with a 2HP motor, rated at 230-208 volts with approximately 10 FLA @ 230 volts. The spec'd OCPD is 30 amp.

To supply this motor, we have a long run of 400' from the meter with 240 volts supply (242 measured).

In an extreme situation of minimum wire size (10 AWG) with triple the inrush current of FLA (30 amps) we would get a voltage drop of approximately 10% down to 216 volts which is apparently within the nameplate rating of the motor.

Why is large voltage drop a problem if the operating voltage is within nameplate rating on motor?

that is...

If the name plate says "230-208 volts", why would 216 volts be a problem?

We are aware of many solutions all involving a varying amount of cost and effort (larger wire, buck-boost transformer, etc) but we do not understand the root of the issue.

We have been warned of damaging the motor in short order if we deviate from the recommendation of 1/0 AL wire in any way but the recommended wire size would only have a 1.5% voltage drop @ 30 amps. We are trying to understand why the recommendation. Is it more than a voltage issue?

• The motor likey wires differently when attached to 208 vs 230 systems. Nov 30, 2016 at 16:48
• The motor can be wired for 115 or 230-208. We cannot wire for 230 or 208. Nov 30, 2016 at 17:11
• With a long feeder the wire size should be upsized to limit the voltage drop to 3%. Allowing the motor to run at lower voltages will cause brown out conditions causing higher current draws and increased heating of the motor. Some motors will stay in start mode and not make run speeds causing motor failure. Nov 30, 2016 at 17:50
• @edbeal "...allowing the motor to run at lower voltages..." than 202 volts? (Which is a 3% voltage drop from 208 volts) Nov 30, 2016 at 18:08
• The question references inrush current. This does not even take into account that operating current is much lower and the voltage would be well above 230 volts during normal operation given we would never run 10 gauge wire 400 feet no matter what for a 30 amp OCPD. That is the operation mode in question is only for a few seconds or less out of the total operating time. Nov 30, 2016 at 18:09