Smart Guy question! - Electrical related (3 phase)...(let's see how good you are!)

a reply to: butcherguy

Well, it wasn't actually a phase to phase short. Because it was at the distribution panel when the conductor came loose it immediately de-energized, so when it contacted the other phase it wasn't hot. Then that conductor re-energized on the same phase. In other words, the lug the conductor came loose from was the (line side) one energizing that conductor (not the other end. If it would have been the other end of the conductor, well, bad ju-ju then!)

In any case, I agree, normally one would expect a big KA-BOOM when something like this happens.

It was just a total freak incident. Probably a once in a lifetime event (I hope!).

a reply to: Flyingclaydisk

Ok, thanks for the clarification. For some reason, I pictured a hot conductor making contact with another phase that was also hot. Makes sense now.

originally posted by: Flyingclaydisk
Got a major fault alarm notification on a 200 kVA UPS going crazy, in a major data center. All sorts of alarms going off. Panels over-temp, things over amp...nothing makes sense.

Okay...some background. For whatever reason this is a 208V 3p input UPS, stepped down from a 277/480 V 3p 75 kVA transformer. In the middle we have an Automatic Transfer Switch and a twin 600kW generator setup. Okay, solid set up. Input voltage to the rectifier is 208 VAC 3p, to the batteries.

Something is going "BAD" wrong! Lugs in the service panel are getting hot (200+ degrees F). UPS is showing faults galore.

We get called. Crazy voltages on the neutral. Okay, let's start the checkout and see if you can figure it out....

Here's what we find. I go in and check the rectifier voltages and get the following (yes, I know it's crazy).

A-Ground = 208
B-Ground = 208
C-Ground = 208

All good, right?

A-B = 480
B-C = 480
AND...
A-C = 208 !!!

What happened?

This was measured on the output side of the maintenance bypass transformer!

Temps are going up in the panels. Something is going haywire. Shutting down the bypass and the distribution transformers means the data center goes dark (not an option!). Time pressure is ON!

What is the problem??

Someone fed it coffee. From Starbucks. With SOY milk. Yuk.

a reply to: Flyingclaydisk

Slightly off...odd tolerances in wiring? Glitch in voltage regulation, bad heat sink(s)? Dunno....IM A GUITAR PLAYER.

Roadies wire my stuff...I just blow up Marshalls...and mixers...and monitors...and...hey Clay? I don't belong here!!!

Leaving....(slams door)...

a reply to: mysterioustranger

LOL!!

Hey, if people didn't break stuff, and/or stuff didn't wear out/fail, there'd be nothing to do!

ETA - Try and not slam the door this time, okay?

[Quietly installs easy slam hydraulic door dampener]

[Crosses voltage on the flux capacitor and shorts the suburb]

[Takes wrong hat, a ladies raincoat and a duck billed umbrella from coat room in the dark and exits]

No one heard a thing.

Someone didn’t use their torque wrench on the install, that’s an NEC requirement.

a reply to: Nickn3
Or didn’t torque it down correctly

a reply to: Nickn3

In the "FA" (Failure Analysis) report...we found exactly that.

Electrician got lazy and tired. It was after hours, and he was trying to pick up overtime work, working double and sometimes triple shifts (for extra hours). Foreman wasn't monitoring him close enough. GF (general foreman) was only watching the money, not the hours. Supt. was trying to plan out about (9) jobs running 24x7, three shifts, had over 100 guys working for him, and mistakenly sent over some volunteers to do a trouble job without researching what'd they'd been doing recently, or how many hours.

Electrician was working alone, doing what he was supposed to do, then went to break and got called off by another foreman to work some other hot issue...and he forgot what he'd tightened and hadn't tightened.

No excuses. People could die. Fortunately no one did, but our FA process really does drill into root cause.

a reply to: Thenail

I'm still thinking he didn't torque it down at all really, just snug and moved on, until he got a torque wrench.

No, it wasn't aluminum conductors, but it was still bad all the same. Again, no excuses! Ever!

ETA - Probably snugged it down with his allen wrench as tight as he could get it by hand and then forgot to check the torque figures later. As you know, that's not going to cut it.

ETA 2 - BTW...Check your PM's. Sorry for the delay in response!

a reply to: Flyingclaydisk

I know nothing about electricity so can say with absolute confidence that you are all wrong and the problem is / was a rats nest.

If you need more electrical help, you know where to come.

So who won?

a reply to: Flyingclaydisk

Maybe , who really knows . Or torqued everything and ended on c phase and got distracted with a phone call or anything else . Always good to torque everything and put sharpie marks across the bolt so you know it’s torqued . I just did a torque report , said if it was a lug or breaker what size and what torque for every bolt on every breaker , panel , gear , and transformer in there . Well thanks man , it was an interesting thread right up my alley .

originally posted by: Flyingclaydisk
a reply to: Thenail

My apologies for the delay in responding! Got pulled away on something else, then life.

Somethings loose ... Check your c phase tightness ... Do you want me to come there and fix it for you lol .

BINGO!! We have a winner!

Electrician who made up the Distribution panel back in an electrical room about 400 yards away didn't get the C phase let torqued down properly. Conductor came loose from the lug and sprang over and made contact with the A phase, hence the readings.

I never would have believed it unless I saw it.

As it turned out it was another Master Electrician (such as yourself) who deduced the same thing. "Only way this could even be possible is if...". At the same time, one of the lugs in the service panel serving the transformer was also loose, hence the heat issue. The heat issue likely contributed to the fault back at the Distribution Panel also.

That electrician is no longer with the electrical firm who did the work.

Very good! Excellent deduction!

ETA - So you really are "that good"!

Wouldn't that be an open on the C primary and a primary to secondary short there?

a reply to: chr0naut
I think most of us already answered this question . Try reading through the thread , it’s pretty exciting. Thanks again FlyingClayDisk . If you think of any others you should bust em out and I probably have a few humdingers I’ve encountered throughout the years .

originally posted by: Thenail
a reply to: randomtangentsrme

Ok
A three phase panel . You know The big panel say in an office building that houses all the breakers that you can use to turn the power on and off .

It has 3 incoming Hot wires and a neutral and a grounding wire . The 3 hots are black red and blue . They each have 120 volts to ground and 208 volts between them phase to phase . Hence the 120/208 3 phase power . Now if you have a 208 volt three phase piece of equipment you’ll need a black red and blue and green grounding wire typically sometimes a neutral but not needed . This is the 4the time I’ve posted something like this now you understand .

With 208, you are taking 2 hot legs, the white neutral leg, and the green grounding leg.

I'm very familiar with 3 phase, as it comes into a building or off a generator. You always need a neutral. You can even tie the neutral to the ground if need be. But you cannot just have hots without a neutral and expect a circuit to close.
Such instances always end in failure.

When it comes to 120 you are taking one of the 3 legs of power from 3 phase and converting it to single phase. As there is only 1 phase that you are dealing with. And when you go to 208 (or 240) and use 2 hot legs they are not in opposite phases so they are still in the single phase category.
With all respect, my Wiki citation did a better job of showing why I am correct, than your own assertions. You need a neutral to complete the circuit. You do not need a ground, but it's best for safety.

a reply to: randomtangentsrme

With 208, you are taking 2 hot legs, the white neutral leg, and the green grounding leg.

With 208 single phase, you have TWO hot legs.
With 208 three phase, you have THREE hot legs.

a reply to: randomtangentsrme

Wow you are an idiot. A first year apprentice electrician is way smarter than you . I’ve explained this 8 times and you’re not any closer to grasping it. I explained three phase but you don’t get it.
You have no working knowledge of electricity in any form.
Ill correct you one more time then after that I’ll assume you’re trolling because no one is this stupid. First year apprentices are smarter after two weeks of class

1- you can’t just tie the neutral to the ground , that’s the most idiotic thing I’ve ever heard , you bond it at the first point of disconnect .
2- you don’t need a neutral for 208, I just wired a 208 volt hand dryer in a bathroom . No neutral needed .
3- do you know what a generator does lol , it fires up when you lose power and runs your critical loads and turns back off after power is restored .

Why do my 3 phase rtus not need a neutral mostly anything 3 phase doesn’t need a neutral .
If you have a 120/208 panel than it’s obviously 3 phase . It’s pretty easy to tell because it has 3 hots. Black red blue . A 2 pole breaker is 2 hots 208 volts . Does hand dryer and heaters and stuff .it’s still 3 phase power but you’re using two legs only . If a piece of equipment is 3 phase then it probably takes 3 hots and a ground . Maybe a neutral but doubtful. Go watch some you tube videos or something

a reply to: randomtangentsrme
To get 208 you need opposite phases
A and b phase lol
A b or c phase on 3 phase
You can’t use the same two phases .

You should be off this thread . Giving wompy Jenky electrical advise is not good . If you don’t have any experience at all don’t be on here acting like you know what you’re talking about . Of the 500 people I’ve worked with as an electrician, you’re by far the biggest idiot if ever heard from . Get out of here and quit giving electrical advice

a reply to: butcherguy

Don't you mean 240 single phase (split phase) (not 208)? Typically, residential power is delivered to a residence as 240 (split) single phase. Meaning two hot legs of 120 VAC at 180 degrees out of phase with each other.

With 3 phase (let's say 208), each phase is rotated 120 degrees from the previous phase. Consequently, if you multiply 120 volts times the sq. root of 3 you get 208 volts, hence the phasing angle of each phase with respect to the others. Same for 480/277. So, if you have a 120 3 phase panel, each of the hot legs are 120 volts. To get a 120 volt circuit you tie one of the hot legs into the circuit via single pole circuit breaker in the panel. To get a 208 volt circuit you use a 2 pole breaker which attaches across two of the hot rails in the panel.

In a residential 240 volt system, both of the 120 phases are 180 degrees out from each other (hence the "split phase" terminology used in some areas). In this arrangement, a 2 pole breaker across both hot rails results in 240 volts which is typically used for ovens, heaters and dryers, etc. I honestly don't think I've ever encountered 208 volt split phase system.