Okay Electrical Wizards, this one's for you (???)

did one of the Phases get switched? Someone replace a transformer wrong so the wrong phase was being created?

Story doesn't check out. Would have had 0 volts in between phases if you re energized two wires with one source voltage

a reply to: rickymouse

I was going to answer that bank B batteries were not connected. That would have been wrong as they got a reading.

The cable FCD is talking about is thicker than your thumb and is very rigid. The bolt that connects it to the panel was hooked up but not tightened to spec. As current flowed through that circuit, the metal heated up and essentially "loosened" the bolt (not quite, it weakened it's holding capacity until it popped off). Of all the places a loose cable with live voltage could go, it bridged with circuit C at the only connection that would not cause a complete short or explosion! The batteries in bank B we no longer charging in this configuration. It ran until the alarm sounded that they were no longer charged and the unit failed to the unprotected muni power! They were running off of muni power with no failback to UPS.

At least that is what I understand. Kind of like a Wheatstone bridge circuit but with no fail-safes or resistors!

You couldn't have had continuity through all 3 fuses in your scenario. Sounds like one of your electricians didn't want to admit he made a mistake and you had a blown fuse. I have run into this problem before.

He probably checked voltage on the load side of the fuse, saw 277v and declared the fuse to not be open but in reality it was the back feed voltage he was measuring. Also made that mistake in the past.

Sorry, not back feed voltage, source voltage from a phase

a reply to: xxspockyxx

There are no "fuses", not on this power...only breakers. So that's wrong.

We didn't have continuity on all three phases. Only continuity on two phases.

Sounds like your electricians didn't want to admit they don't know what they're talking about!

Frankly, we shouldn't have had continuity through any phase. (not phase to phase anyway) Maybe phase to neutral (which there isn't), and then measure phase angle, but, well, you know.

a reply to: xxspockyxx

Nonsense, read the description up above.

originally posted by: Flyingclaydisk

originally posted by: dashen
B&C shorted in two places?

I'm going to award it to you, dashen! You are so incredibly close we're practically splitting hairs here.

If you would have said just "B & C are shorted" you would have the correct answer, but there's more to it than that.

You see if the B & C conductors actually "shorted" you'd have a phase to phase short (bad ju-ju).

What had happened was the B conductor came free of the lug in the distribution panel. Because cable that big is so stiff, the B conductor wanted to go back to a straight position. Because the feeders entered the lower left side of the panel they were all bent to the left to make up the lugs. When the B phase came loose it sprang to the right contacting the C lug in the panel. So, technically it wasn't a "short", but rather an open that then re-energized itself on the C leg, hence the 277 reading between B and C. It didn't have to touch in "two" place, but rather only one in this scenario.

We believe that the electrician who made up the connections didn't torque the lug properly. Then when it was under load and heated up the conductor came loose and ultimately came free. That electrician lost his job.

And now you know...the rest of the story.

If the b phase came into contact with the c phase therefore both being supplied by the c phase on the load side of whatever how would you have 277 between the 2?

a reply to: xxspockyxx

Stop talking about "fuses"! If you know power, you know there are no true "fuses" anymore. There are all manner of breakers and interrupts, but no "fuses". If you're talking about utility power, sometimes these are referred to as "fuses", but they're really just breakers / disconnects / interrupts.

a reply to: xxspockyxx

depends on where you meter it!

edit...think about it.

a reply to: Flyingclaydisk

People don't use fuses?
Again if both wires are being supplied by the same phase how would you have voltage between the 2?

Not in your scenario.

a reply to: Flyingclaydisk

Electrical engineer and you say "where they meter it"? Also fuses are used everyday by millions of people. Sorry but your story doesn't check out.

a reply to: xxspockyxx

Okay, one more time for ... you....

If you meter the circuit on the load side you will see 277 phase to phase (based on the above).

If the failure would have happened the other way, on the line side, it would have been a phase to phase short. Agreed?

I really don't have a lot of compunction to argue this fact any more. You can call BS all you want. I was there!

originally posted by: xxspockyxx
a reply to: Flyingclaydisk

People don't use fuses?
Again if both wires are being supplied by the same phase how would you have voltage between the 2?

The same way you have voltage between 2 energized phases!!! DUH!!!

originally posted by: Flyingclaydisk
a reply to: xxspockyxx

Okay, one more time for ... you....

If you meter the circuit on the load side you will see 277 phase to phase (based on the above).

If the failure would have happened the other way, on the line side, it would have been a phase to phase short. Agreed?

I really don't have a lot of compunction to argue this fact any more. You can call BS all you want. I was there!

I'm calling bs. Your sorry doesn't check out.

a reply to: xxspockyxx

Remind me not to hang out around you with open switch gear!!!!

a reply to: xxspockyxx

Do the math!

originally posted by: Flyingclaydisk
a reply to: xxspockyxx

Do the math!

what math? You test phase to phase on 2 wire connected to the same phase on the load side of anything you will have 0 volts. Story doesn't check out. You may be not telling the story right.