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Need wiring advice from RPC to 3-phase sub-panel. Problems with single phasing?

J_R_Thiele

Stainless
Joined
Jan 22, 2003
Location
Columbia Missouri
dalmationgirl61

I suspect the 50 amps you referenced was off of the idler nameplate. The manufacturer is using specially wound Baldor motors, with extra turns of wire to boost the voltage in the generated leg. There should be another nameplate for the RPC as a whole, and that is the one the NEC is referring to. The size of the idler determines the largest motor that can be started initially- but starting more motors if lightly loaded adds to the overall capacity. For example the RPC has a 20 HP idler, and the largest motor to be started is 12 HP. Start 2 of those and you have the equivalent of a 44 hp idler (20+12+12=44). If you then start a 16 hp motor you are at the 60 hp maximum FOR THE WIRING AND SINGLE PHASE BREAKER they recommend. The single phase breaker is to protect the RPC system and its loads, not just the idler.
 

J_R_Thiele

Stainless
Joined
Jan 22, 2003
Location
Columbia Missouri
Here is a drawing of what you need. The 125 amp breaker is single phase, so T3 cannot run through it

Having a magnetic switch controlling the 3 pole contactor will shut the RPC down if you lose power. It does not protect from phase loss. If you are concerned about that there are several options that can shut things down if you loose the generated phase. The problem is the risk of a short voltage drop triggering them. You could wire in an ICM450 to set off an alarm- but not shut anything down. It could also be wired in to shut things down. Discussions and diagrams are in this thread. 3 phase starter circuit
 

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dalmatiangirl61

Titanium
Joined
Jan 31, 2011
Location
BFE Nevada/San Marcos Tx
Data tag is on the idler, and clearly marked Phase a matic, not Baldor, but it does look like a Baldor tag, there is another tag on capacitor box, just name, model and serial#. Had not ever concerned myself with it, but after reading the code noticed the discrepancy, if anyone ever questions it I will point to mfr's recommendations.

I'm using a 3ph breaker so there is an empty slot, but those question marks indicated my uncertainty of doing that. I see in your schematic the breaker comes first, makes sense and easy enough for me to swap locations, thanks!

I know I had some ICM450's, think they all sold, but cheap enough for some peace of mind and easier than wiring in individual meters.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
That is a perfectly reasonable setup, it's pretty much what I run.

It does not "guarantee" that you cannot single-phase the system, but it cuts the possibility significantly.

Additions might be an overload on the idler, which opens the contactor on overload, so that all power to the 3 phase is cut if the idler has a problem.
 








 
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