How do you measure voltages on a rpc ?

[Brain Coral]

Hello all,

I just finished wiring in a 10hp RPC. From the RPC I have run a 12 AWG 3/wire and ground extension cord with a 30 amp 3/wire and ground plug on the end of it. I can then plug different machines into the plug as I choose.

Here's a pic of the plug...



I would like to know what the voltages are at the plug end, but am not too sure how to do it.

Brian

 

[JimDawson]

Measure;

A to B
A to C
B to C

That will give you the voltage between each leg. Between 2 of the legs I would expect it to be at line voltage, but I'm not sure what the manufactured leg will measure unloaded. Under load I would expect it to be close to the other two.

When you do this, please let us know what the voltages are. I have never taken a reading on a RPC.

 

[Karl_T]

Measure;

A to B
A to C
B to C

That will give you the voltage between each leg. Between 2 of the legs I would expect it to be at line voltage, but I'm not sure what the manufactured leg will measure unloaded. Under load I would expect it to be close to the other two.

When you do this, please let us know what the voltages are. I have never taken a reading on a RPC.

I put in cheap voltmeters as Jim outlined. They cost about $10 each on eBay. Put them in the RPC panel.

Tuning an RPC is important, that's why the voltmeters. You can then start adding or removing run caps to get all the voltages within 10%. This step costs almost nothing and will improve the performance of your equipment.

 

[JimDawson]

Karl, let's assume no voltage drop for this question. Would the voltage be the same on the manufactured leg in both the loaded and unloaded condition? I've never set up a RPC, so I've never had a chance to look at the output.

 

[Brain Coral]

Thanks for the replies...

I guess that I should further explain that while I do own a voltmeter and ran a new circuit from my main panel and wired in the RPC and motor, I don't know how to safely and properly use the voltmeter to test the voltages.

I do know that I must turn the voltmeter to the ACV setting, but then I'm not sure if I have to check the voltage inside the RPC panel or can I check it at the plug end somehow... ?

Brian

 

[Karl_T]

Karl, let's assume no voltage drop for this question. Would the voltage be the same on the manufactured leg in both the loaded and unloaded condition? I've never set up a RPC, so I've never had a chance to look at the output.

. The "wild
You actually have two manufactured leg voltages. The "wild" leg to ground or neutral seems to be meaningless.

If you have a large RPC motor horse, compared to machine.Voltages will change when loaded, but not terribly. They tend to sag with load.
Anyway, you need to watch both loaded and unloaded. I add or remove a cap, record numbers:repeat.


I'm not the EE here. I am just repeating the work of a guy named Fitch that became an established expert on this. He's a EE - power specialty. I can give you his email.

 

[Karl_T]

Thanks for the replies...

I guess that I should further explain that while I do own a voltmeter and ran a new circuit from my main panel and wired in the RPC and motor, I don't know how to safely and properly use the voltmeter to test the voltages.

I do know that I must turn the voltmeter to the ACV setting, but then I'm not sure if I have to check the voltage inside the RPC panel or can I check it at the plug end somehow... ?

Brian

Same number either place, do it where its easy for you

 

[Ulma Doctor]

Measure;

A to B
A to C
B to C

That will give you the voltage between each leg. Between 2 of the legs I would expect it to be at line voltage, but I'm not sure what the manufactured leg will measure unloaded. Under load I would expect it to be close to the other two.

When you do this, please let us know what the voltages are. I have never taken a reading on a RPC.

Hey Jim,
a RPC will have basically 3 different voltages dependent on measured phases.
i measure them all the time, the generated leg on an UNBALANCED RPC can be as much as 30 volts @ 240v
common readings look like this 242/236/212 unloaded
lightly loaded they look like 238ish/230ish/205ish on a 5hp motor
of course balanced you can get them within 2% or slightly less with some work.

 

[JimDawson]

Hey Jim,
a RPC will have basically 3 different voltages dependent on measured phases.
i measure them all the time, the generated leg on an UNBALANCED RPC can be as much as 30 volts @ 240v
common readings look like this 242/236/212 unloaded
lightly loaded they look like 238ish/230ish/205ish on a 5hp motor
of course balanced you can get them within 2% or slightly less with some work.

Thank you, that's very helpful.)

 

[Brain Coral]

Back again...

I guess that what I need is the actual techique used in measuring the voltage. I am not entirely comfortable with it at this point. I don't want to short something out, nor get a shock.... :yikes:

Here's a pic of the panel...



And here's a pic of my cheapo voltmeter...



Brian