TS started in reverse (3-phase)

[Larry Fox]

I have an scmi slider that has a 3-phase motor in it. I get the third leg via a RPC which I start via a button above the saw. The button activates a coil on a NO contact that starts the RPC. Anyway, the other day I pushed the button to start the RPC and the contact chattered a bit but still pulled in and closed. I started the saw only to realize it was running in reverse. I turned the saw off, let the converter spin down and restarted the works and everything was fine. Anyone have any thoughts about what happened? I have done this same operation hundreds of times in the last without incident - this was the first time.

Thanks in advance for your time.

[Bill Orbine]

RPC is rotary phase converter? Swap any two of the three phase lines to correct the reverse. As for the chatter, the RPC should be running before starting the saw. Are you using the appropriate RPC for the power requirement of the saw?

[Rod Sheridan]

Larry, your RPC started up in reverse rotation.

Don't start the RPC with a load connected............Rod.

[Larry Fox]

Thanks for the replies guys.

Bill - I understand the reversing of any of the two legs to switch the direction but I have started this saw hundreds of times and this is the first time anything like this has happened. I am likely to chalk it up to "one of those things" unless it happens again.

Rod - I suspect you are right but it was not under load when it started. I have a specific sequence I use without exception: RPC, dust collector, saw. I even have a little light that comes on when the RPC is running that I glance up at every time - it's almost a ritual at this point.

Oh well - I will keep an eye out for it happening again.

[Charles Lent]

Check the contacts on your RPC and saw contactors. A worn contact can provide 2 phases to the saw causing it to start in either direction. If the contact is high in resistance it could cause the chattering. It's more likely the saw contactor but check and clean the contacts in both.

Charley