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Topic: Share your worst electrical nightmare!

Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 08-08-2004 12:03 AM

quote:
While I like the looks of an operating Mercury vapor rectifier such as an 866, those big glass bulb mercury arc rectifiers scare the pants off of me! I keep my distance from those! Yikes!

Thank gods for that, since we don't want to see you with your pants off!! [Smile]

Been told by an old-time operator that some of those mercury rects made some pretty evil noises too.

Stephen: Thanks for the links, they are great!!

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 08-08-2004 01:37 AM

About the best you will see out of a xenon igniter is around 70-100 KV at a few milliamps. Keep in mind, however, that it is not DC coming out of there, it is actually an RF pulse.

RF burns really hurt and take a loooooooong time to heal.

Josh

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 08-08-2004 01:56 AM

Josh: What was the deal with the neon xfmer and salt water cap? Jacob's Ladder?

RF burns are indeed really nasty. Anything with a higher frequency than normal AC mains (50 hz or 60 hz) tends to have greater net energy. More penetrating power (Burns are deeper), etc.
It was explained to me that's why my aircraft shock threw me so far, it was 400 Hz. (Standard AC for most aircraft.)

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Phil Hill
I love my cootie bug

Posts: 7595
From: Hollywood, CA USA
Registered: Mar 2000

posted 08-08-2004 02:28 PM

Actually a Jacob's Ladder uses NO capacitor.... it relies on the hot yellowish flame of a Low Freq AC arc's heat currents to pull the arc up the ladder. A cap would make that arc very noisy and a bright bluish-white that would basically just sit there at the shortest gap.

More than likely that bad boy is for a Tesla Coil or LOUD spark noise generator?

Also, I've never seen a neon sign xmfr with a current rating more than 30 mils. I suspect JJ is putting 2 in parallel? Nasty boy! I'm referring to the transformers, not Josh... But! Hey, we can talk... [evil]

What are you using for your salt water caps? I use Miller Lite beer bottles. I would use Corona bottles, but we ALL know, corona is a bad thing for HV...it robs much-needed energy for a coil. [Roll Eyes]

C'mon Josh! Tell US! You bait us and then hang us out like last night's underwear!

quote: JJ
...will see out of a xenon igniter is around 70-100 KV at a few milliamps.

True, but keep in mind that the cap B4 the gap stores a hell of a lot of energy. In many designs without bleeders and while the voltage is not high enough to jump the gap, the cap will store the HV a LONG time and will give you a nasty bite.

>>> Phil

[ 08-08-2004, 06:45 PM: Message edited by: Phil Hill ]

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Bob Healey
Film Handler

Posts: 93
From: Milford, CT
Registered: Sep 2001

posted 08-08-2004 07:53 PM

My worst electrical disaster:
At college, I was providing lights for a Sunday afternoon jazz concert using the school's equipment. They contracted with an off campus 3rd party to provide the sound reinforcement. I didn't have to arrive for setup until 11am for a 1pm start (the lights were pre hung/focused, everything just needed to be powered on and tested.). At breakfast, around 9am, one of the people who worked with the campus sound crew saw me and told me I needed to get down to the auditorium ASAP as I had no power. He also suggested I grab the 3 phase extensions from storage.

In the auditorium, the lighting dimmers were setup to be powered off a camlock drop and the sound system was designed to use a 30A 3phase twist outlet. The outside audio company decided that they had to use the cams for themselves and that I could deal. The school electrician was onsite as our ground and neutral camlock connecters were not compatible and he had to splice ground and neutral into the box directly.

The dimmer rack was designed to be run off of camlocks or a pair of 30A 3phases lines in parallel, so I asked the electricial to hook a second twist outlet into the box to go with the one normally reserved for sound. He goes and wires it in on the box end, and I connect the extensions to the dimmers. He energizes the two breakers on the wall box. I energize first one input, then the other on the dimmers. There is a loud pop and most of the building blacks out.

It turns out that the electrician crossed the black and the blue phases when he hooked up the second outlet. The input breakers on the dimmer rack tripped, the breakers on the wall panel back stage tripped, the breakers in the panel feeding the auditorium tripped, and the breaker in the mains panel that fed that section of the building tripped. The audio guys were ready to kill me over the shock to their equipment. The electrician also discovered a breaker panel that he didn't know about when things didn't come back on after he reset the breaker in the mains panel. Didn't blow the mains, but came close.

Got everything sorted out by noon with a 1pm performance. I have reduced power, so I used less lights than normal, resulting in the corners of the stage (with no performers) not being illuminated. Expecting something to overload during the show, I had set a pair of follow spots to illuminate as much of the stage as possible, then closed their shutters.

During the show, the conductor moved over to one corners and a soloist moved to another. I went and attempted to bring up extra lights which resulted in the dimmers tripping their input breakers. I left to sprint backstage through the auditorium, and my assistant, in his haste to get the shutters open on the followspots, forgot they were on and accidently turned them off.

The dimmers at full load want about 58A of current/phase, I had 60A/phase, normally 100A/phase. Shortly after that abused the rack died, and I found out the campus electricians had also done such wonderful things to the rack as swapping a hot phase and neutral or a hot phase and ground in other temporary hookups in non-standard venues. The audio company has me pegged as a total incompetent for not keeping the lights on during the show, even though they took my power supply (only drew 5A total on all phases), and pretty much left the electricial to improvise whatever power he could for me.

Oh, and the act was the US Army Jazz band.

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 08-08-2004 11:44 PM

Bob: I can relate to your situation. I worked for an A/V company up North and camlocks and dimmers caused us the most drama. The closest call came at the end of a show when one of the crew guys decided to "help" by disconnecting the feeder to our main distro box (200amp 3-phase). He had already disconnected the ground and had twisted the neutral cam when I saw what he was doing and screamed at him. I spent the next ten minutes ripping this idiot a new asshole and told him and everyone else on the crew to keep thier f..king paws off of the feeder.

Why was I so upset? Because our entire house P.A. and stage monitor rig as well as the dimmer pack (64 channels) WAS STILL POWERED UP!! [Eek!]

Tip for those dealing with camlock power hookups:

CONNECT = GROUND, NEUTRAL, BLACK, RED, BLUE (Or Whatever colors hot legs are)

DISCONNECT = BLUE, RED, BLACK, NEUTRAL, GROUND

You don't want to be holding a live camlock breaking a loaded neutral!! It's not pretty! And yes, as any power lineman will tell you, you CAN get bit by a neutral line!

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William Hooper
Phenomenal Film Handler

Posts: 1879
From: Mobile, AL USA
Registered: Jun 99

posted 08-09-2004 03:01 AM

This thread would be interesting if it was "What did you say when you got the crap knocked out of you fooling with electricity?"

quote:
Actually a Jacob's Ladder uses NO capacitor....
[...]
More than likely that bad boy is for a Tesla Coil or LOUD spark noise generator?

My guess is a Tesla coil.

You can make an excellent spark noise generator with 110 AC, a 110v light dimmer, a doorknob cap, & a spark gap. String up an antenna, & it's a nice little thing to have if folks in the apartment next door play their stereo or TV loudly.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 08-10-2004 06:42 PM

The cap was the begining of a tesla coil that was never really finished. I just wanted to make a bad ass loud spark gap, and it worked. The sign tranny was salvaged from a jewelry store in the mall during remodeling. It may have been 60ma, I dont really recall.

as for the gap, it would run for a few seconds, then stop. used a glass gallon jug full of brine and wrapped with tin foil on the outside. Its a wonder I didnt burn the place down.

I always wanted to build a coil, just didnt have the time to build one. I do own several books on the subject, though.

The current project operates at only 3800V but can supply about 1A, and as a bonus, 1KW of FM power as well [Wink]

Josh

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Bob Healey
Film Handler

Posts: 93
From: Milford, CT
Registered: Sep 2001

posted 08-10-2004 09:12 PM

The style of camlocks we use have safety interlocks so the only way to connect them is green white black red blue and the only way to disconnect is reverse order. There are hard plastic boots over the standard cam cables and interlocks on the sockets to prevent out of order hook up/disconnects. Doesn't stop someone from trying it live though. Same dimmers as above failed a month later on me. According to a sound guy with an ammmeter, i had 40A-30A-20A flowing in the hot phases, 70A flowing through neutral, and a scary 20A of current on ground.

I'm normally the one how does hookups/disconnects, but that show was out of my hands. Incompetent administration. Hires outside company, and gives them wrong info about power, leaving me with me. Sorry, still ticked about this.

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 08-10-2004 09:20 PM

quote: Josh Jones
used a glass gallon jug full of brine and wrapped with tin foil on the outside. Its a wonder I didnt burn the place down.

Whoa!! I wonder what the capacitance of that setup would measure!!

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 08-10-2004 09:51 PM

quote: Bob Healey

I'm normally the one how does hookups/disconnects.

I, too, am the only one who does the tie-ins, except for the campus electrician. The electrician(s), the production manager and me are the only people who even know where the key to the padlock on the disconnect is.

The electrician isn't going to come to the theater on a Saturday just to do a silly tie-in. The production manager isn't going to get his hands dirty doing manual labor. Nobody else has the balls to even go into the electrical vault by themselves. That just leaves little ol' me. [Wink]

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Bob Healey
Film Handler

Posts: 93
From: Milford, CT
Registered: Sep 2001

posted 08-11-2004 07:09 PM

quote: Randy Stankey
I, too, am the only one who does the tie-ins, except for the campus electrician. The electrician(s), the production manager and me are the only people who even know where the key to the padlock on the disconnect is.

The biggest problem with that is my campus's electrician's done what it looks like you're about to do in your picture. And he energized the circuit afterwards.

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John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002

posted 08-11-2004 07:54 PM

Bob Healey writes, "The dimmer rack was designed to be run off of camlocks or a pair of 30A 3phases lines in parallel...It turns out that the electrician crossed the black and the blue phases when he hooked up the second outlet."

Is there a requirement that L14 connectors have the phasing in any particular order? I was under the impression that it was not safe for devices to assume any particular order at all.

--jhawk

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David Buckley
Jedi Master Film Handler

Posts: 525
From: Oxford, N. Canterbury, New Zealand
Registered: Aug 2004

posted 08-11-2004 08:21 PM

Camlocs in the hands of the inexperienced can lead to real disasters.

quote: Tony Bandiera Jr
You don't want to be holding a live camlock breaking a loaded neutral!! It's not pretty! And yes, as any power lineman will tell you, you CAN get bit by a neutral line

Its worse than that. Once the neutral is disconnected on a three phase rig, without the solid reference the neutral floats to some voltage between zero and the phase-to-phase voltage. The corollary of this is things connected between phase and neutral (ie all single phase stuff) will have undervoltage and overvoltage conditions imposed on them, as the neutral voltage wanders aimlessley. Things will blow up.

Happened in a computer centre I worked in once. Through poor installation and non-existent maintenance, the neutral burned out in a switchfuse. The repair bill was over 100K UKP for new power supplies for dozens of computers, from PCs to Sun E10K. Very nasty.

quote: Bob Healey
...40A-30A-20A flowing in the hot phases, 70A flowing through neutral, and a scary 20A of current on ground...

Ground current seems a bit high [Smile]

Many sparkies dont realise that non-linear loads (stage light dimmers, computers) can cause the neutral current to rise above the phase current, due to addition of harmonic currents. Time was when NEC permitted weedy neutrals on USA wall sockets, as there was this theory that the neutral current could never rise above the phase currents, but once office blocks full of PCs started burning down, that got changed.

When I was a kid I used to proud that I was always getting shocked from one thing and another. My (late) mum told me I got my first shock at age 3 from unsrewing a wall socket. Nowadays I'm happier to say I've only had one belt in 25 years, and that was 'cos I was stupidly tring to switch off a light with a security switch, like someone else did hereabouts... Only on 250V not 110V [Embarrassed]

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 08-11-2004 09:24 PM

Electricians around these parts are pretty good, actually. Both of the main guys are licensed Master Electricians in the city. I would trust them to do most anything as long as I have had a chance to meet with them in person first. That way we are both on the same channel with regard to what work needs to be done and any special conditions that need to be met. There are a couple of assistants who I don't know well enough to trust, but they never get dispached to my building because the two other guys are supposed to be in charge of anything that has to do with the main feeds to the building(s).

As to making and breaking Camlocks: I ALWAYS make bottom up (G-N-øA-øB-øC) and break top down (øC-øB-øA-N-G). Heck, it's such a habit with me I even do it that way when I'm soldering up XLR cables. Aside from any safety concerns, it's just the way I organize my work to keep things neat and tidy.

And... In case there is any question... My member picture is totally dummied up. None of those Camlocks were even connected to anything, much less energized.

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