You are probably right, the chart is just for installed
wiring. However lots of motors of 1/8 hp or greater
capacity are run on extension cords that are as long or
longer than the maximum run listed for 14 gage wire.

Grant Erwin wrote:

You're right about one thing - 14 gage is the minimum wire size this
chart goes down to. I think it says you can't wire a circuit with
smaller wire than 14 gage and still be to code. - GWE

George E. Cawthon wrote:

Ted Edwards wrote:

Bob Swinney wrote:


Charts of this type giving motor hp or motor kva instead of amps are usu.
based on the amount of current a motor would "draw" if working fully loaded.

Perhaps Grant's chart is based on starting current which is typically
quite a bit higher than run current, even at full load. While to brief
in proper operation to overheat the wires, I have seen a case where a
small generator could keep an appliance running but couldn't start it.

Ted


The chart says it is from Dayton Electric Co., so I guess
some one could ask them. Based on just the figures given
for 1 hp and under single phase 115V, we know it isn't for
2% voltage drop. And it isn't based on inefficient motors,
reasonable starting currents, and practical knowledge, based
on other published data and experience. For example, 1/8 hp
motors don't require 14 gauge wire, they run just fine on 16
gage and even 18 gauge wire. They even run just fine on 14
gauge extension cords that are 200 feet long.

Another example is my compressor is rated at 5 hp, but we
know that is a lie and is probably close to 1 hp. It runs
just fine from a building that is supplied by about 100 feet
of 10 gauge wire. That is in stark contrast to the chart
that indicates 4 gauge wire would be required for a 1 hp
motor.