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Old 02-13-2020, 12:15 PM   #21
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The OP'ster said that the motor was 1Φ. But if you look at the motor specs on the drawing, the amperage and HP listed seems to correspond to a 3Φ 2.3HP motor @ 208-220V.


If it is a 1Φ motor, the amperage listed seems low for a 2.3HP unit. We cant know for sure unless we see a motor tag, especially since the terminal labels seem odd. It may be a European or Asian 50Hz unit with labels like that. Hard to tell from here.


It can be a 1Φ motor, where the auxiliary winding serves start and run functions. Start mode would use both capacitors, and the run mode would have just the run cap in the circuit. But the amperage listed seem low for that scenario.


The circuit shown could work for either scenario, 1Φ or 3Φ, depending on what the capacitor values were, but the print does not indicate what they are.
The RBM potential relay appears to be a special, since it is not listed on the cross reference chart, leading me to believe it is calibrated for a voltage other than standard US one.
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Old 02-13-2020, 02:58 PM   #22
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I will chalk this up to “what I learned today.”

Good stuff here. Thanks.
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Old 02-13-2020, 05:35 PM   #23
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Never said it was a Rotary Phase Converter. I had said it looked like the OP had a phase converter. I drew that conclusion as the drawing looked very similar to one I had worked on the previous day. Apparently I am mistaken.

I don't have any real life experience with RPC. Any time I've needed 3 phase, it was there.

When you posted about the RPC, I googled it and did find many diagrams extremely similar to the OP. I thought I fugged up

The contactor had me confused a bit, but then micromind posted about the 3 phase overload, and I remember coming across that once ... thanks micro


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The reason for the 3 pole contractor and 2 poles connected in series is cause it most likely has a 3 pole electronic O/L relay. These relays need to see roughly the same current on all 3 poles, if there's current on only 2 poles, it'll trip on single-phasing.
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Old 02-13-2020, 09:49 PM   #24
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Originally Posted by CMP View Post
The OP'ster said that the motor was 1Φ. But if you look at the motor specs on the drawing, the amperage and HP listed seems to correspond to a 3Φ 2.3HP motor @ 208-220V.


If it is a 1Φ motor, the amperage listed seems low for a 2.3HP unit. We cant know for sure unless we see a motor tag, especially since the terminal labels seem odd. It may be a European or Asian 50Hz unit with labels like that. Hard to tell from here.


It can be a 1Φ motor, where the auxiliary winding serves start and run functions. Start mode would use both capacitors, and the run mode would have just the run cap in the circuit. But the amperage listed seem low for that scenario.


The circuit shown could work for either scenario, 1Φ or 3Φ, depending on what the capacitor values were, but the print does not indicate what they are.
The RBM potential relay appears to be a special, since it is not listed on the cross reference chart, leading me to believe it is calibrated for a voltage other than standard US one.
The drawing is pretty standard for a 1Ø motor that does not have a built-in centrifugal switch to disengage the start winding. Most submersible pump motors and refrigeration compressors use this starting system.

I thought the current seemed a bit low too but looking in the Leeson motor spec book, most of their 2HP 1Ø models draw anywhere from 8.2 to about 10 amps.

Capacitor-run motors will draw less current than their induction-run counterparts because the run capacitor will result in a higher power factor and thus, lower current.
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Old 02-14-2020, 07:03 AM   #25
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I don't have any real life experience with RPC. Any time I've needed 3 phase, it was there.

When you posted about the RPC, I googled it and did find many diagrams extremely similar to the OP. I thought I fugged up

The contactor had me confused a bit, but then micromind posted about the 3 phase overload, and I remember coming across that once ... thanks micro
I haven't worked on an RPC style converter in quite a few years, and the ones I did seemed to be unique, each with it's own twist, to the area they were in. I assume that is like everything else, where it's the electrician or vendor in the area at the time doing the work that determines what products are installed.

The ones I've hit lately either have a step up transformer in the same enclosure or separate and are of 3 different manufacturer's, again all similar, but also unique. I've been after them for years to change them our when they fail to a step-up transformer and a VFD, but so far one has been done.
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Old 02-14-2020, 11:23 AM   #26
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I've furnished and installed one RPC in my life. It was for one specific large pump. I've never seen one used for multiple motors, or a whole shop.
Have any of you guys seen this ?

The one guy that had a thread going, and continious problems, is the only place I heard of doing that.
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Old 02-14-2020, 02:02 PM   #27
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I've furnished and installed one RPC in my life. It was for one specific large pump. I've never seen one used for multiple motors, or a whole shop.
Have any of you guys seen this ?

The one guy that had a thread going, and continious problems, is the only place I heard of doing that.
I’ve a r-mix plant that runs entirely off of 1 of 2 50hp Arco RPC’s. The original owner/builder believed that overkill is underrated. The service is a 1000 amp 240 single phase service. The voltage balance was way out of shape when we took over, ac was ~ 275 and bc was ~ 285 volts. I moved some caps around and eliminated a few also. Putting the caps in the combo units to be switched in and out was the key. The plant works well, but the constant errrrrrrr all day long can grate on your nerves.
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Old 02-14-2020, 03:19 PM   #28
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1000A 1 phase 240V service... that's nuts!
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Old 02-14-2020, 06:03 PM   #29
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1000A 1 phase 240V service... that's nuts!
Like I said, old owner, rest his soul, was a certified agricultural engineer, figure out how heavy it needs to be then double it for safety. Truth be told, there was plans for a small screening plant to make their own aggregate for the concrete and it never got past the gathering up the equipment stage. The old guy was a ball of energy, but there is only so much daylight in a day.
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Old 02-14-2020, 06:10 PM   #30
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I’ve a r-mix plant that runs entirely off of 1 of 2 50hp Arco RPC’s. The original owner/builder believed that overkill is underrated. The service is a 1000 amp 240 single phase service. The voltage balance was way out of shape when we took over, ac was ~ 275 and bc was ~ 285 volts. I moved some caps around and eliminated a few also. Putting the caps in the combo units to be switched in and out was the key. The plant works well, but the constant errrrrrrr all day long can grate on your nerves.
746Wx50=37,300W/240V=155A each
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Old 02-14-2020, 06:24 PM   #31
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746Wx50=37,300W/240V=155A each
746 watts in a perfect world with no losses.
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Old 02-14-2020, 06:31 PM   #32
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So about 300A conversion on a 1000A service ?
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Old 02-14-2020, 06:43 PM   #33
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So about 300A conversion on a 1000A service ?
Probably about 1000 watts per hp, so 200 amp a piece or so. Both running with a 100 amp single phase load in the control room = 500 amp. With the farm engineer multiplier, 1000 amp.
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Old 02-16-2020, 12:06 AM   #34
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The drawing is pretty standard for a 1Ø motor that does not have a built-in centrifugal switch to disengage the start winding. Most submersible pump motors and refrigeration compressors use this starting system.

I thought the current seemed a bit low too but looking in the Leeson motor spec book, most of their 2HP 1Ø models draw anywhere from 8.2 to about 10 amps.

Capacitor-run motors will draw less current than their induction-run counterparts because the run capacitor will result in a higher power factor and thus, lower current.

Been a busy week, so a little late on the reply. I haven't been involved with 1Φ submersible pumps in the past, just above ground units, so I made time to look at some Franklin Submersibles for context.

You were right on the money with the amperage and power factor of these type units. They list the currents and resistances of each winding in their catalog specifications, as well as capacitor values. Very handy when troubleshooting. See the attached PDF catalog page below.


Since they run fully loaded at all times, the power factor is easily adjusted for one point of load, with capacitance, and theirs is shown near .95PF. They even list, additional maximum capacitance the can be added to quiet a noisy motor.


Another interesting fact was that they require a class 10 overload protection, to not void the warranty. Which is what we saw in the OP setup.
Pretty efficient setup when you can control the load point at one setting. Not so much true with other pump setups.


Refrigerant compressors would be very similar. Sealed unit, with internal fluid cooling, and one point of load.


Pump motor data specification page
Franklin Submersible Motor Data.pdf


Franklin Manuals Page for those interested in more information.
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Old 02-16-2020, 02:01 AM   #35
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I've furnished and installed one RPC in my life. It was for one specific large pump. I've never seen one used for multiple motors, or a whole shop.
Have any of you guys seen this ?

The one guy that had a thread going, and continious problems, is the only place I heard of doing that.

It's pretty common for shops in the rural areas to use them for machine shops and wood shops. Far less cost than stringing primary lines for miles and upgrading services. RPC's have a sine wave output, and that can be an advantage on multi motor equipment, with some across the line motors and some driven by drives, such as a CNC machine.

Most users of equipment don't have the skills to convert a machine to a VFD drive or 1Φ operation, so a RPC is the easier option for them, and less expensive.


In the RPC thread with Mobius87, they weren't having continuous problems with the RPC setup, just the one Asian bar twisting machine. It was pretty small compared to the RPC it was powered from. And that can create problems. A smaller RPC idler motor and capacitor bank would likely run that small motor with no issues, but in this case a small VFD, would likely be the best solution.


For an example of a machine shop powered by a RPC, have a look at Keith Rucker & Vintage Machinery, and few videos from a well re-guarded RPC vendor about his shop.



A typical forum discussion on RPC vs VFD from several perspectives, would give you a better understanding of the need.
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Old 02-16-2020, 01:04 PM   #36
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It's pretty common for shops in the rural areas to use them for machine shops and wood shops. Far less cost than stringing primary lines for miles and upgrading services. RPC's have a sine wave output, and that can be an advantage on multi motor equipment, with some across the line motors and some driven by drives, such as a CNC machine.

Most users of equipment don't have the skills to convert a machine to a VFD drive or 1Φ operation, so a RPC is the easier option for them, and less expensive.


In the RPC thread with Mobius87, they weren't having continuous problems with the RPC setup, just the one Asian bar twisting machine. It was pretty small compared to the RPC it was powered from. And that can create problems. A smaller RPC idler motor and capacitor bank would likely run that small motor with no issues, but in this case a small VFD, would likely be the best solution.


For an example of a machine shop powered by a RPC, have a look at Keith Rucker & Vintage Machinery, and few videos from a well re-guarded RPC vendor about his shop.



A typical forum discussion on RPC vs VFD from several perspectives, would give you a better understanding of the need.

Thanks ! Good information

His new meter socket, and first panel has pass through lugs,but I don't see a main disconnect in there like he says ?
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