Line to ground voltage

Question

Our plant has a 3 phase line to line connection when I test the voltage from line to line in the supply side of the main breaker it reads 230 volts but when I test line to ground, line 1 reads 196 volts, line 2 is 111 volts and line 3 is also 111 volts. Are these readings ok? When the main breaker is turned on, the reading from line 1 to ground is 0, line 2 to ground is 230 volts and line 3 to ground is 230 volts.

Answer 1

Sounds like “Wild Leg Delta”. Is the high leg orange, or marked with orange paint or tape?

First, a side trip through history

The Philippines used to use North American style 120/240V “split-phase” with neutral in the middle: 240V between legs and 120V from leg to neutral.

After independence and particularly after the “distance ourselves from America” fervor which gripped the country in the 60s-80s, the Philippines resolved to harmonize with the rest of Asia on 230V single-phase (derived from 400V three-phase “wye”). New neighborhoods were easy enough, but what to do with the older USA infrastructure? Simple solution: outlaw use of the neutral wire. Now you have single-phase 230V with a center ground (which is actually safer) and works fine with Eurasia appliances.

What on earth is wild-leg?

Normally, with delta, you use some bias transformers to create a “center ground”. So at 240V you have around 137 volts to center. Normal enough. However, in 240V “delta” installations, American customers wanted to be able to run 120V appliances without a transformer and additional service.

“Okay”, engineers said. “We’ll give you a center-tap halfway down one leg. You can make that point neutral and ground. That will give you 120V to two of the legs. But, the third leg will be a higher voltage, so watch out!”

Indeed, the wild leg is leg / 2 x sqrt(3) or 208V on 240V.

NEC says the wild-leg must use orange wire, or be marked with orange tape or paint.

Enter the Philippine neutral putsch

Of course, when the government banned use of neutral, that did nothing to change how the transformers were wired. A 240V 3-phase transformer may still be wired and grounded for wild-leg, even though neutral is no longer in use.

That is what you are looking at.

From the sound of it, they also down-jumpered the transformer from 240V to 230V, lowering the wild leg voltage from 208V to 199V.

Answer 2

It sounds like a wild-leg delta supply with a poor earth followed by a ground fault from phase 1 to ground in your plant.

Check ground isolation (test the insulation between the phases and ground) on your plant.