ECN Forum Forums Code Related Discussion NEC & other Code issues Delta Skelter

I am stumped here. There is a 3 ph 4 wire panel, voltages to G are 120,120,240.
There re only two X-formers on the pole, the bracket is visible where the third can may have been....

Sparky,
Sounds like an open delta with a wild leg, but the 240 to g should be closer to 208.
Don

Sparky,

I agree with Don, delta, with center tap. Usually you should get:
a - g 120
b- g 120
c - g 208

a- b 240
a- c 240
b- b 240

What are your phase to phase voltage readings?

Sparky, go here.

http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm

Roger

ameterguy,
the readings are as you've stated.sorry 'bout that...
( 'twas a dark rainy night, etc, etc..) The high leg is marked white, removing the panel cover is like taking the bra off the fat lady....


Roger, yep that's the beast.. is the grounding conductor common to the primary??

Sparky, The grounding conductor could be common to both. The real caution here would be lets say you were going to make this installation verses the utility. If your primary were an ungrounded delta and you were going to provide a grounded system, the grounding would have to be isolated on the secondary side.

Roger

There one more variation of the open-delta arrangement used by electric utilities, and fairly common in some areas—that is open-wye grounded primary, open-delta secondary. At: http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm you can visualize it looking at Fig.1-1 Y-∆ layout. Now remove the primary winding at the ten o’clock position that is connected to L2. The hi-side wye point has to be connected to the hi-side neutral conductor [not shown on 1-1.] so there are still three conductors serving on the primary side of the bank. Now, on the secondary, delete the winding at the 2 o’clock position. [Sometimes this is incorrectly called ‘two-phase,’ but that designation is reserved specifically for 90° phase-displaced voltages.]

In areas where the multigrounded common neutral is used, it saves a fused cutout and wire for the unneeded third phase. {For geeks only—In some areas where lo-side delta voltages are needed, a grounded wye-delta bank is prohibited, for it acts as an undesirable ground source and can induce high currents in the common-neutral conductor during hi-side faults.}


[This message has been edited by Bjarney (edited 06-08-2002).]