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American Rotary DIY panels. A.R. says need delta wound motor...?


Oct 29, 2017
Guys. I've been in need of a rpc for a while now as I shut my welding business down and moved out of my shop that had 3 phase. Looking at the American Rotary diy panel's as they fit my budget much more than buying a complete unit from them. I just need to find the right motor (haven't acquired anything yet for this).
Most of the motors I'm seeing on the used market (mainly HGR surplus in Cleveland oh.) are wye wound in 230V.

American Rotary specifys on their website you need "A delta wound 230v motor preferably in the 17xx rpm range"

Much of the research Ive done on this in the last two days, guys on this forum and other forums say it doesn't matter if you have delta or wye wound idler motor....

What gives? Why does American rotary spec a delta wound motor? Gonna call them tommorow and find out from them but want some input here. Thanks very much!


Aug 16, 2014
silverdale wa
I couldn't figure this out for a while so I worked the numbers out a handful of years ago. There is no difference between delta and y... Except with regard to heat distribution.

Most motors are concentric windings, machine inserted, not lap or mush windings (which require a lot of work by hand to put the coils in the motor) this may be part of the problem. Bigger motors with lap windings are going to have better thermal conduction from 1 coil group to another, so there will be less difference thermally between delta and Y.

As such, when you compare photos of burned out motors which were overloaded on single phase. Delta motors generally have 1 burned coil, y motors have 2. The general rule is a delta motor can develop 50% nameplate hp as a single phase motor, a Y motor 57% (but most round up to 2/3rds.) This is due to the thermal distribution, not any electrical difference.

Electrically and magnetically the motors are the same, but thermally the delta winding puts 75% of the heat in 1 coil and 25% in the other two coils, when used as a single phase motor.
A Y motor puts 100% of the heat across just 2 windings, the third is unused.

Now: there may be an advantage to the delta RPC; The power factor correction capacitors connected from both line 1 and 2, to generated leg 3, to boost the generated leg, on a delta motor those capacitors do not cause an increase in current through the primary coil. (Coil A line 1 to 2) No increase in heat in the main coil and the power factor correction decreases the current drawn by the main coil. The two other coils are both providing the generated leg and they are providing power factor correction.

On a Y motor the capacitors do cause current to flow through both coils a and b and c, in order to boost the generated leg.

There may be a second advantage to delta motors.. good quality delta connected motors have to be wound with a coil group that provides a better sine wave, so that they do not have circulating currents.


Jul 23, 2001
Buffalo NY
Only my personal observations, but...
I have seen that Delta connected motors
do not buzz nearly as much as Y connected
Good info on thermal loading. Pretty cool.
I have a delta 12hp RPC that
will start a 10hp load fairly easily. It has
balance caps and runs very quiet. I am sure
the 1200 rpm motors make it quiet also.
I have spoken to the tech at North American
Phase Converter (not American Rotary),
and he tells me that all they
sell now are Delta connected RPC motors.
Finally some people may have also discovered this.



Sep 12, 2007
Northern Illinois
I suspect the issue is passing a grounded neutral to the downstream equipment. I see the original post was a month ago. Was American Rotary ever contacted, and what was their response?