determine legs in 3 phase

On Friday, January 16, 2015 at 12:59:49 PM UTC-5, Cydrome Leader wrote in rec.crafts.metalworking:

I'm going to be setting up shop of sorts in a commercial space with some
dodgy electrical service that's been tinkered with over the years. It has
208 volt 3 phase, which I wish to extend into my space.

There should be a A, B and C legs, but how is this order determined by
testing?

In testing you normally use black, red and blue for live low voltage and brown, orange and yellow for high voltage connections.

For low voltage, black fingernail polish or tape for 'A' connections, red for 'B' and blue for 'C'. Use green for Ground-only connections and white or Grey for neutral connections.

For high voltage, brown fingernail polish or tape for 'A' connections, orange for 'B' and yellow for 'C'. Green is still used for Ground-only connections and white or Grey for neutral connections.

 

Crosspost much ?

Anyway, sometimes there is a difficulty with determining which phase is leading and which is lagging. For (example) a reciprocating compressor it does not matter if it uses reed valves. But other things, it might matter.

Many years ago my Father ran horizontal boring mills. Big uns. One machine he said first of all had shitty coolant flow. What's more every once in a while the impeller of the centrifugal coolant pump would come unscrewed. The company lived with that problem for a long time until he got there and got sick of it.

He figured out that the pump was running backwards. Just switch any two wires and it reverses the motor. Any two, doesn't matter which two as long as it is a delta configuration. There is no reason to use the Y configuration on a little shitcan motor like that.

For some reason the machine itself ran the right way. Go figure, I did not wire it.

 

On Fri, 16 Jan 2015 22:50:01 -0600, Martin Eastburn
<lion...@consolidated.net> wrote:

On 1/16/2015 11:59 AM, Cydrome Leader wrote:
I'm going to be setting up shop of sorts in a commercial space with some
dodgy electrical service that's been tinkered with over the years. It has
208 volt 3 phase, which I wish to extend into my space.

There should be a A, B and C legs, but how is this order determined by
testing? I've not seen any electricians carry around an oscilloscope, so
there has to be an simpler way. Grab a small 3 phase motor and put
alligator clips on it and fuss around until it spins in the right
direction?

If you are concerned with rotation issue - just swap two and it reverses.

There might be a 'wild' leg, might not. Put wild on lights and heaters...

Use the two good and a wild for real 3 phase. If you put a computer
on a wild phase you can have issues...

Martin - 377 three phase in shop from my 208 single phase.

Sure. And just in case you've scared the fire department, maybe here's how to tidy things up to standard per code:

"The high leg service conductor of a 4-wire, 3-phase, delta connected service must be permanently marked orange or identified by other effective means [NEC Article 230-56], and must terminate according to the following: meter termination: ANSI requires termination on the C phase; panelboard and switchboard termination on the B or center phase [NEC Article 384-3(f)]. "