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Using start capacitors to start a 12 wire RPC.

Feb 7, 2024
Mead Washington
I replaced my old 15 hp motor with another I found. I cant get it to start using the start capacitors and am wondering if I wired it for the WYE configuration if I could just leave it like that without switching over to the Delta. If im understanding things right!!! There would be no load on the phase converter motor. I also checked all 6 windings on the motor and got a consistent .8 ohms which seemed odd. Could setting out in the weather cause a lower resistance. This is a tefc motor.
Thanks in advance
Please post motor nameplate and what configuration you've got it wired in.

I would expect parallel delta for 240V operation. Parallel wye would give you only about 57% HP, with reduced inrush current.
This is the name plate. Second is the coil connections we used and third image in the lower right corner seems to show a different method. I did compare this motor resistance to another 20 hp 12 wire motor and came up with similar but a little lower resistance. I put a clamp meter on one leg of the 230 and it was up around 150 peak, (1 or 2 seconds) I didnt check the other side though. I have run capacitors going from each leg to the center along with 3- 300-360 mfd 330 V start capacitors from one leg to the center through a second timed contactor. We have checked resistance of all contacts. Main contactor is an old AB size 2 and I think the start contactor is a newer Square D size 1. I cant remember the exact numbers on the run capacitors .
Thanks in advance.


  • 15 Hp motor nameplate.jpg
    15 Hp motor nameplate.jpg
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  • 15 HP Coils.jpg
    15 HP Coils.jpg
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It's not surprising that you cant get it to start. According to the diagram you made and posted the windings are not connected properly. it needs to be connected in the double delta configuration for low volts (240V) for an across the line start.
Here is the WEG connection diagram, use the left one ΔΔ double delta. For the run mode.
WEG  12 lEADual Vpltage Wiring_Diagram.jpg
Another drawing by another manufacturer. For a similar comparison.

To start with, remove all of the capacitors and try to start the motor with a pull rope around the shaft to get it rotating. If it starts and runs in this mode, then you know the motor is good.

Once you get past this point, then you can work on getting your caps reconnected. You should not have a wye center point to connect them to, given that your windings are configured in a double delta. I would suggest that you reconnect them how they were to your old motor for starters and then adjust from there if necessary. If the replacement motor is the same size as the old one, you should be fairly close.
It's embarrassing!!! I was in a wreck a few years back that was not my fault. I think others were looking at their cell phones. I had a brain injury and was compensated nicely for making bone head drawings like the one I made every now and then. I actually have to have my wife double check my bids because I have no idea when they are going to go sideways. The motor was actually wired right. We found the problem. I have a couple of 3 phase distribution breaker panels in our shop. We found that our made up leg was going to ground causing the idler motor to not start. I haven't investigated it any further yet. We Megaohmed the two motors. The old motor I pulled out was reading around 275 to 350 at 1000v. we tested with two testers and got the same reading. The motor (12wire) I have in there now was reading over 2200. Would the 275 to 350 readings be bad enough to cause the motor not to work? We test vehicle induction loops and figure anything below 35 to be bad. Could I use the same 35 on the mega ohm meter for a pass or fail on a motor?