no reading from "B" phase

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georgeswe

georgeswe

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The Republic of Southern California
I belive we are working with a 3 wire ungrounded Delta, we have a 240 from Phase A to ground and 240 from phase C to ground. However, we do not show a reading from Phase B to ground. We do get 240V betrween A+B A+C B+C. I read that old systems like this used to have a ground sensor located on it since if there was a ground fault you would not know. Edison has been out and said that we were not reading it correctly and that it was correctly wired. But not sure if that statement would be true to what I have after the gear or not. I also do not have any nameplate as to what system this is. The customer forgot to call me so I could speak with the Edison trroubleman. Originally, we thought this was Hi-leg delta but with what readings we took and the absence of a neutral wire. Any troubleshooting help would be appriciated.
 
It could be a purposely desiged corner grounded delta or it could have originally been installed at an ungrounded delta and one phase has gone to ground. Is the main fusible or not ?
If it was designed as a grounded system "B" phase should not have a fuse.
 
George, if this is a corner-grounded Delta, which it is measuring as, there should be a point of obviously-intentional bonding of the 0v-reading conductor in the main disco, just like the MBJ in a 'normal' service, and that conductor should be colored as a neutral.
 
LarryFine said:
George, if this is a corner-grounded Delta, which it is measuring as, there should be a point of obviously-intentional bonding of the 0v-reading conductor in the main disco, just like the MBJ in a 'normal' service, and that conductor should be colored as a neutral.
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While the grounded phase is required to be identified as a grounded conductor, I have never seen one so identified, but I have only worked on about 10 such systems.
 
don_resqcapt19 said:
While the grounded phase is required to be identified as a grounded conductor, I have never seen one so identified, but I have only worked on about 10 such systems.
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But, there are other tell-tale signs, such as 'dummy' fuses and the aforementioned MBJ, right?

I think step one is to determine whether the grounding is intentional.
 
A high impedance grounded delta will also show a 0 voltage to ground on "B" ?

Could be a ungrounded delta at the transformer but grounded at the meter/disco, or high impedance grounded anywhere in between? I've seen both as well as some using single phase panels as a grounded "B" panel, but not in any new installs.

Years ago had a guy run a 120 volt circuit to a panel like that un knowingly that it was a grounded "B" with 240 to the neutral bar, well he got a big surprise when he energized the circuit and let the smoke out of the load:mad:
 
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