Find three phase "wild" leg

Is there some reason you can't just take a meter and measure the voltages to neutral? Should get 120V on the regular legs and a lot higher (forget exactly) on the wild leg. Besides that the wild leg is supposed to be marked orange.

Pete C.

Oh, sorry, re-read your post and realized you were not talking about a wild leg delta utility connection.

If you can get access to a 240v single phase circuit nearby that is not fed off the converter you should be able to identify the non-wild legs by measuring between the hots on the single phase outlet and the hots on the three phase outlet. Should get close to 0 when you are measuring across the same hot.

Pete C.

measure voltage from three ends of the plugin to two ends of 220v single phase. The one three phase end with non zero voltage vs. both single phase legsis the wild one.

i

If I understand you correctly, you have a rotary phase converter that generates 3 phase voltage from a "normal" single phase circuit. I'm not sure if this applies, but a three phase circuit breaker panel wired

in a delta with the center of one winding grounded (called a Delta-high

leg") has a "wild" or "stinger" phase - the 2 "normal" phases measure

120VAC to neutral or ground, but the "wild" or "Stinger" phase measures

around 208V to ground - the actual value can vary due to the load. Any phase gives 240 VAC to any other phase. If you encounter this > I'm moving a wire EDM into my shop tomorrow. Its presently in a shop with a

"Karl Townsend" wrote in message news:kgs8h.1418$ snipped-for-privacy@newsread1.news.pas.earthlink.net...

It doesn't really matter, Karl. If you must know, then trace the wiring back to the converter. Single phase legs one and two power the converter AND your EDM. The manufactured phase comes only out of the converter and to your machine.

LLoyd

It doesn't matter for a manual machine like a Bridgeport, but for a CNC machine it often does matter. In many cases the control electronics are powered from a single phase and on the older units that power supply may not like living on the less stable wild leg and can cause all kinds of weird problems.

Pete C.

Yeah... there is that.

Sorry: It matters, Karl.

LLoyd

And except that I'd failed to consider there may be some single-phase control circuitry that really wants to see a stable 120V from one incoming leg to neutral.

LLoyd

Lloyd sez: " It doesn't really matter, Karl. If you must know, then trace the wiring

Agree with Lloyd. Except that Karl didn't say whether his new EDM is a

3-phase or single-phase machine. If it is single-phase just wire it directly to the 240 vac source coming from your power panel. If the EDM is a 3-phase machine, a direct connection to the RPC is the way to go.

Bob Swinney

Unless you have a five wire sytem, with Hot, Hot, Wild, Neutral, and Ground, you need a transformer to convert the 220 across the Hot and Hot to 120 volts. You should not be tying into the "Neutral" unless it is really the Neutral, and not the Ground. Pete

According to :

And this really should describe three phase from a typical rotary converter -- as the two 240V feed lines come straight through, with the rotary converter simply generating the third phase.

The only time this could be different is when you have a two-part rotary converter -- with an electric motor driving a separate alternator, in which case the output is isolated from the input, unless some part is intentionally wired through.

but the only two-component ones which I have seen were by the Georator company, and produced 400 Hz three phase output. Since you want 60 Hz input and 60 Hz output, there is no reason to do something as expensive as this.

Enjoy, DoN.

According to Lloyd E. Sponenburgh :

And in particular -- for the BOSS-3 through BOSS-5 machines (at least), which use stepper motors, DC power for each axis to drive the stepper motors is derived from a different phase, and *any* phase which shoots too high in output voltage could blow a bank of transistors switching the stepper motor's phases. Those transistors were run pretty close to the maximum voltage (based on what was available at the time), and so they are pretty easy to fry.

I'm not sure about the servo-motor equipped later machines, BOSS-8 and later, I think. They may be more tolerant of overvoltage.

Good Luck, DoN.

Sure. But it's usually the case when running an RPC that those leads are all available, even if not broken out to the equipment.

LLoyd

It sounds like we agree. If the equipment does not have five wires going to it, it should have a transformer for the 120 volt loads. IF there is a five lead cord, Then it could have 120 volt loads without a transformer, but only if it had all five leads. Safety matters. Pete

Even if it's Delta in and has a transformer for the 120V, that transformer should be wired across the two "real" phases and avoid the manufactured phase.

Pete C.