How do you measure voltages on a rpc ?

[Ulma Doctor]

you can take the measurements for output at the plug, you'll have little chance of hurting yourself.
you'll notice one leg on the plug looks different,
it will either be bent inward [leg in,30amp] or bent outward[leg out, 20 amp] that is your ground leg.
you won't use it for testing at this point.
start up the unit, test across 2 hot poles of the plug and record your reading.
move 1 lead to the other hot pole you have not tested and record your reading.
move the other meter leg back to the first pole to get the last reading and record.
that will give you all three phase to phase voltages .

at this point ,you could also put one lead to the ground pole and test ground to phase for each pole as well and record your readings.

i hope i didn't confuse you more, if i did LMK, i might be able to explain differently

 

[Karl_T]

my vote for easiest place to measure is your terminal block labeled CAB
looks like C and A are you L1 L2 line voltage

CB would be anther voltage of interest
AB would be the other

Use the pins of your voltmeter to touch the screw heads in this terminal block

The plug will give the same values - do which ever is easier.

Karl

 

[Boswell]

I suggest that if you are not 100% confident in using the meter probes inside an open and energized panel that you measure at the plug This is the safest. I am not saying that you can't measure in the open panel safely, but YOU need to KNOW that you can do it safely, to be safe.

just my .02 USD

 

[Phils69]

Looking at the pic of the panel you don't have your 3 phase RPC motor connected yet, unless I am just not seeing it. Without that you aren't going to be able to check any generated voltages.

 

[Brain Coral]

I'm back with some readings...

I also have a 5hp RPC and thought that I would measure that one as well, while I was at it.

10hp RPC...

C-A 249v
C-B 242v
A-B 257v

5hp RPC...

L1-L2 249v
L1-L3 252v
L2-L3 260v

I didn't check to ground, but here's a start. Just so you know, before I turned the breaker on and started the RPC, I cut some cardboard to provide a small measure of safety in a shield so that I couldn't come into contact with the capacitors...

Thanks for all of the helpful advice...

Brian

 

[JimDawson]

I would say that is pretty close. Normally +/- 10% is close enough. Your readings are closer than that.

 

[Brain Coral]

Looking at the pic of the panel you don't have your 3 phase RPC motor connected yet, unless I am just not seeing it. Without that you aren't going to be able to check any generated voltages.

Hi Phil,

That pic was taken before I completed the wiring. Both the 3-wires from the motor and the 3-wire extension cord share the CAB block. Also, I ran a 50 amp cicuit with #8awg 3/wire with ground to the RPC panel.

Brian

 

[Brain Coral]

I would say that is pretty close. Normally +/- 10% is close enough. Your readings are closer than that.

Hi Jim,

Well, that's nice to know. I've had the 5hp RPC running for a few years now and didn't know how well it was performing.

Brian

 

[Phils69]

I thought I was missing something. Who made that panel you have in the pic? Looks a lot like my 7.5 hp one.

 

[Brain Coral]

Hello Phil,

The panel was made by WNY Phase Converter and Supply. I am very pleased with the voltage readings and the ease that it starts the motor. You can barely hear the starting power contactor tripping out because it happens so fast. It also has discharge resistors on the start capacitors, which is a nice safety feature.

It retails for $185.00 plus shipping. I forget what the shipping was to my door, here in Canada, but it was very reasonable.

The idler motor is a 10hp Leeson TEFC motor at 1760 rpm. It must have real good bearings, as it takes a long time to come to a stop after shutting the RPC down. I was given this motor, along with 4 others for free from a local monastery.

Brian