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

ugh if B and C shorted together then they would read 0 volts

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.

a reply to: Flyingclaydisk


It can take the heat?

a reply to: Galen65

No, not necessarily. See above.

Interesting.

originally posted by: Flyingclaydisk
a reply to: Galen65

No, not necessarily. See above.

Right back to my original answer and the backfeeds....
It had become a single phase system....

a reply to: Galen65

If they were truly "shorted" it would have tripped the mains in the panel.

Actually, not single phase, but more like 2 phase.

a reply to: Galen65

Backfeed was somewhat correct. It was the rest of your answer which was not.

a reply to: anonentity

Yes.

I once picked up a welding lead...440...it had faulty insulation.
I was wearing rubber-soled boots, so i just felt a little tingle.
Then I leaned against a steel beam.
Holey Good-Garshk!
An arc jumped between my teeth! Heating my toofs to a few hundred degrees in the process.
I now do not jack with the Gawds, oh, Holy Damn! of electricity.

a reply to: skunkape23

Oh, I could tell ya' some crazy S#, believe me!!

One time myself and another guy were carrying a metal door leaf down a exterior steel 6 floor stairway at a chemical plant (this was back in my college days). About halfway down we decided to rest for a second and set the door leaf down on the stairs. The second we leaned the door up against the side of the building the door instantly welded itself to both the stairs and the side of the metal building! Talk about a WTF moment!! Oh, and it was raining too! We just froze not knowing what to do. The edges of the door were glowing red and you could hear the current flowing through the door leaf (like this humming sound). "Don't touch anything!!!" We walked down to the bottom (without the door obviously), and jumped with both feet off the last step so as not to be in contact with the stairs and the ground at the same time.

We found out later that a big 6-pack 480 welder had grounded out on the stairs energizing them. The building was grounded, but the stairs weren't and were isolated from the building. One wrong move that day would have fried us both!

a reply to: Flyingclaydisk

I worked with a couple of line men who have felt the sting.
One had the soles of his feet blown out.
Another that has a metal skull-plate and a leg that drags.

a reply to: Flyingclaydisk

Not fun. I had an odd one at a radio station. 480V 3 ph incoming. Had some alarms and on reading saw AB 480 BC 0 AC 478
but on the legs A-gnd 270 B-gnd 180 C-gnd 270! Turned out the one leg had dropped way down the line and there was enough capacitance to show substantial voltage. Took a large tower light bulb to each leg, on A and C got a good light, on B got a really bright flash that dropped to 0 volts. Wierd.

I once made a carbon arc device using the carbon rods inside a D battery. I mounted them in a wooden jig and when I touched the tips it smoked, then blew out the house fuses.

Come on, I was 10 years old!

Was there an environmental cause?
Did mind quad get in?

a reply to: anotherside

Well, yes and no. The root cause was heat (so I guess that's environmental) due to a improperly torqued connection. When the current rose the lug also heated up and expanded. This allowed the feeder to come loose from the lug and cause the fault by contacting another phase. However, because the feeder which came loose was immediately de-energized (due to coming loose from the source) to zero volts (hence the low volt critical alert) there was no phasing issue. The feeder then sprung over and made contact with the C phase making conductors B and C be on the same phase (hence the 277 phase to phase readings). From the UPS's perspective it was still under-volted on B phase. Because the B phase de-energized before contacting the C phase there was no phase to phase short, and because the load had already switched to bypass there was no load to create an in-rush current issue on the B phase. So, B just elevated itself to the same potential and phase angle of C. Had the load remained on line, or the lost connection happened at the load end of the feeder, there likely would have been a hell of a fire (minimally) if not an explosion. (think - like 6 tons of molten acid infused gel exploding in every direction, like napalm on steroids).

It was just one of those days where you go buy a lottery ticket on the way home from work!

a reply to: Flyingclaydisk

Magnetic induction?

Edit I see you gave answer above lol

a reply to: SkeptiSchism

Nope.

Scroll up.

a reply to: Flyingclaydisk

We had designed a air conveyor for plastic pellets. We used 3 inch dia. aluminum tubing. We sent grounding wires with the unit, but the installer chose not to use them. When they started the system it started throwing sparks from the static that it generated.

a reply to: JIMC5499

Oh, I'll bet!! That stuff generates static like nobody's business. Saw dust is another one. Had some guys ask us once how to build a dust collection system in a wood shop. We told them to make sure the tube were all bonded to ground. They just thought we were being overly cautious. ..until one day they had a fire in one of the vacuum tubes from static buildup igniting the sawdust. Fortunately they caught it before it became a building fire, but they listened after that.