High leg on 3 phase power

It is a red leg delta system. Take your measurement between each phase and see what your reading that a to b, a to c, and b to c all read within a few volts of each other.

The greatest risk you have with your current situation is the possiblity of burning up your single phase 120 Volt equipment if you mistakenly connect it the 211 leg to ground.
 
WOW! I haven't seen this in 20 years. Didn't even know it was still used. Most electricians don't know it ever was. Must be an old building with a lot of 220 double poll breakers. Seems like (I said seems like) it was also referred to as a low voltage 3 Phase system or 240 3 phase. Your machine may be a 480 3 phase. If you get an electrician, I'd make it an old timer. [email protected]
 
J

Jackie Roberts

Obviously you weren't involved heavily in the industrial field if you haven't seen a delta system in 20 years. Any industrial journeyman should be able to tackle open and closed delta systems and yes they are still in common use especially in plants that have mostly 3 phase loads such as motors and welding machines.
 
R
Doug be careful about calling it a "B-high" leg I don't know if there are any other places in the country like Long Island, but in Nassau and Suffolk County's the original power authority LILCO brought there high-legs into buildings on the C-Phase. I learned the hard way when a generator made in Ohio came wired with the high-leg wired on the B-Phase while I was accustomed to it entering the building on the C-Phase.
 
First order of business is to convert from 240 volts to 208 volts. Your machine needs 208 volts from A to B, 208 volts from B to C and 208 volts from C to A. So you need the transformer or converter.

One allotment of 208 volts from B to N is not good enough.

Also check to see if your machine has a neutral (white) fourth wire. If so you need three more voltages, 120 volts from A to N, 120 volts B to N, and 120 volts C to N. Here the transformer needs to provide a neutral off of its secondary with those voltage relationships. Do not connect the machine to the neutral you already have.
 
doing a job on a building that has a 3 phase 4 wire delta coming in. all the service entrance conductors were ripped out. at first look thought it was a 4 wire Y system 120/208, all phases were used. in the panel inside, after looking into it more, there was a jumper wire inside the panel, going from phase a-c. I know I can't put anything 120 on the high leg, but unsure if I can put any 240 circuits on it. as it is right now, I think I have to install a sub panel, and move a lot of circuits, because that one is maxed out, because it was rigged.
 
I

Instructor HVAC

I was checking voltage on a 3 phase compressor, upon checking across all legs I was reading 230 volts, however when I went to round on one leg, I was reading 0 Volts to ground. Please explain this condition The building has its own transformer
 
Instructor HVAC... the arrangement you observed is called a Corner-Grounded-Delta. It is a 3-phase, 3-wire system.

I suggest you post a new thread because this thread is the Center-Tapped High-Leg or Red-Leg, or Bitch-Leg, etc. It is a 3-phase, 4-wire system.

Regards, Phil Corso
 
Why don't we call the B-leg or Red-Leg of the 120D/208/249 the Orange-Leg since we're supposed to connect only wires with Orange insulation/markings to it? ...not to confuse it with O in 277/480 BOY.

> This arrangement is known as "bitch leg" or "stinger leg" delta. The middle of one
> leg of the delta is the ground point, rather than the center point of the star, as in
> Y-secondary transformers. The source will appear as a 240V three phase delta to the load.
 
J

James williams

Well Said. Not to say that we all didnt have to learn from someone but this stuff is not a good experiment to do on your own. You will burn up alot of expensive stuff. Especially in automation. Im wiring a whole plant right now and have to look at every machine to the nth degree to make sure nothing that wants 120 is on that high leg. Its quite a pain in the ass but works just as good if done right.
 
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