testing a center high leg Delta

[LarryFine]

I have several industrial customers with Grounded B Phase Systems. They are 3 phase /3 wire systems. A-B, B-C, A-C = 480 v. A- grnd, C- grnd = 480 v. B- grnd = 0v. Distribution gear should be clearly marked as grounded B phase.

Additionally, the grounded phase is supposed to be white (or 'grey') throughout the premises, just as in any other grounded supply. It's also supposed to be opened by disconnects, but unfused (common-trip devices are acceptable).

I've never seen a grounded b phase system @ 208 or 240 volts.

And, of course, you won't. The grounded conductor will be the Y neutral or the A-C CT neutral.

Added: To correct myself, there are indeed 240v corner-grounded Delta systems.

 

[Gary Shumaker]

Carl,

From your post:
Which set up would you say I have if the voltage readings I'm getting are as follows:
Ph A to Grnd & Neutral = 125 vac
Ph B to Grnd & Neutral = 125 vac
Ph C to Grnd & Neutral = 125 vac
Ph A to Ph B = 217 vac
Ph A to Ph C = 217 vac
Ph B to Ph C = 217 vac
You have a wye secondary. Each phase is 125VAC and line-to-line is 217VAC.
The math is rather simple phase voltage x √3 (1.732) = line-to-line voltage.
e.g., 125v x 1.732 = 217v
Regards,
Gary

 

[LarryFine]

With readings of 217v and 125v, I'd say he has an unloaded 208Y/120 system.

 

[ljakic]

It sounds like he may possibly be testing for voltage on a corner-grounded Delta. In which you will have zero volts on the grounded phase. Check voltage by going phase to phase A-B, A-C, B-C. You should have 240V all around.