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

This one is for any electrical wizards / gurus out there. Read carefully...there might be a quiz at the end.

Note: this really happened, and I witnessed it with my own eyes. Anyone who can explain it (correctly) will get a and (2) along with a

Okay, here we go...

A newly installed 200kVA Uninterruptible Power Supply (UPS) in a major mission critical data center alarmed on a fault and switched to emergency bypass (normal utility power). The error on the UPS was "Low voltage - Input - Phase B", "Major fault - Critical" and "Switched to Bypass". The UPS was fed from a 600A 480VAC 3 phase electrical panel. Engineers (myself and others) and Electricians were dispatched immediately to investigate what was going on. I was the lead engineer, and this was serious business!

The electricians (now in flash suits) checked the input voltages and here's what we found...

Phase A to ground = 277 volts
Phase B to ground = 277 volts
Phase C to ground = 277 volts

Okay, so that all looks good, now let's check phase to phase voltages...

Phase A to B = 480 volts
Phase B to C = 277 volts (wait...what???)
Phase C to A = 480 volts

No opens, nothing. Voltage on every phase.

So what happened?

Now, before you say this is impossible, remember I actually witnessed this with my own eyes. We were all standing around scratching our heads. This shouldn't be possible, but there it was...double, triple and quadruple checked with (3) different meters. I didn't solve it at first, but one of the electricians said there's only one possible scenario where this could happen (and it had a 1 in a bazillion chance of happening). What was it?

A couple key points to remember here:
1. There were no opens on any meter reading (i.e. zero voltage)
2. Continuity checked across all three phases

What happened?


edit - I've intentionally left off one (more) test which we did to confirm the problem once we had established a theory of what was wrong.

B&C were shorting and B was touching grounding?

its past my bedtime, and i have no idea

a reply to: Flyingclaydisk


Oh dear,

It is very obvious what the cause is, it is due to "Brexit"......





RA

a reply to: dashen

Very good! You're actually very close, but nothing could be grounded because:

1. You'd have a dead short
2. The mains in the distribution panel would be tripped and you'd have zero volts on all three phases.

You really are pretty close though! I'm "shocked" someone got so close so fast.

As a flunky, once upon a time, now simply bootleg, half-assed residential electrician... I really shouldnt even probably guess...

But the only scenario this reminds me of is issues where someone tries to feed a 240v circuit from a single phase. Usually because of a 'peanut' or half-sized breaker hardware.

So my guess is that B and C have conductors touching somewhere line side of the facility, but voltage is being maintained by some other magical industrial 3-phase equipment that maintains the max 277 volts.

a reply to: Flyingclaydisk

was it arcing and not burning out?

a reply to: dashen

No arcing.

a reply to: JRedBeard

You too are surprisingly close, but no magic here. And no other power source.

(Well, there actually is a generator on this panel, but it's not relevant to the problem)

a reply to: Flyingclaydisk

well im half asleep, so last guess for tonight is that they were all shorting a tiny bit but more between B & C.
off topic, what what the highest voltage youve been zapped at?

I'll give you a hint...

Both of you have actually said the answer already, but the rest of what you said was incorrect.

I would look for a lifted earth on the B circuit.

Not earthing properly.

P

a reply to: dashen

Around 150kV, but then so have you.

a reply to: pheonix358

Nope.

Check wire for outside contact.

Otherwise, it's gotta be resistors.

A blown fuse (B or C) and reading a backfeed from the other.

I'm not an electrician, but when we set up my 3 Phase there are 2 um 'voltage layout' configurations the meter/panel could have come as where one the voltages are the same on all three poles, but the other one is an odd half sort of voltage on one of them.

I cant imagine you dont know that, its actually the problem, but you do have an odd half voltage there so...

a reply to: projectvxn

No resistors and nothing grounded (other than earth ground).

a reply to: Galen65

Nope. No tripped or open breakers, but you are also pretty close!

Geez, you guys are sooooo close!!

a reply to: IgnoranceIsntBlisss

You're most likely talking about 'delta' and 'wye' configurations, but no that wasn't the problem.

edit...the UPS would have never worked properly to begin with if it had been wired to the wrong configuration.

a reply to: Flyingclaydisk

Got converters between your power supply and the panel?

Perhaps built into the power supply?