Are you SURE your transformer is bonded?

[kwired]

Absolutely the installers fault. Unfortunately, several threats of legal action and uneducated installers continued. Some Mfg's were going to put a warning lable on X0, but decided just to eliminate the bond.

And the ignorant installer that connects a neutral to X0 still has problems, and first instinct is that something is wrong with the transformer.

I honestly don't see how the manufacturer is liable for the installers ignorance. The transformer may or may not need bonding jumper installed and it is installers responsibility to know when and why.

 

[sandsnow]

In the early 80's Mfg's did bond X0 to the frame. Once back feeding a standard Delta x Wye xfmr was acceptable, heating issues became common even though the operation and maintenance manuals clearly stated the removal of the X0 bonding strap was required for back feeding. Current X0 factory bonding has been discontinued due to these issues.

Thanks for that. I always wondered why they stopped.

Sadly I'm not surprised at the reason.

The lack of understanding still prevails. Someone recently took a 480 delta to 208 wye XFMR and hooked it up for backfeed and expected to get 480 3 phase 4 wire by connecting the neutral to XO.

 

[pfalcon]

If there is no SBJ then you should have no continuity from any circuit conductor to ground. If you do there is something wrong someplace, and if there were a SBJ, instead of strange voltages showing up there likely would have been overcurrent devices opening. Making the fault location a little more obvious.

If the neutral is inadvertantly bonded someplace, you would likley have voltage readings that would not raise any concern, and you may never know there is a problem until some connection develops a high impedance someplace.

Admittedly, it is a little odd that the system went to 120 volts. The current flowing through the A-phase magnetically couples to the ground. However, since there is an opposite current flow in the neutral, the result is typically somewhere in between. That's why 7 years ago I had 80 volts G-N.

It could be that one of the loads on the system has a connection from A to ground. It doesn't have to be a short circuit, though. It could be a high impedance connection. As long as there is no current flow, it would pull the A-phase to ground voltage.

By the way, this was a single phase transformer.

Here's something interesting. I haven't confirmed this myself, but allegedly, the G-N voltage is back to zero this morning. I don't know what has changed with the loads from last night to today. Possibly just that some lights are not on during the day. I haven't heard from the EC yet. The church called the owner last night, and he could be on vacation. Nevertheless, due care should be taken before blindly applying the bond. I'll have someone checking outlets periodically with an Edison tester, and if/when they get a red light, I'll go back there and see if I can isolate the source.

Nothing odd at all. Old equipment often has leakage across circuits. Inadequate / old / abused insulating materials. Only odd at 120V that some other device wasn't pulling back on the other phase. Think moderate impedance to ground.