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Author Topic: Today's cautionary tale  (Read 5117 times)

Riley Casey

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Today's cautionary tale
« on: February 24, 2018, 10:28:58 pm »

A reminder from the Ministry of Always Meter Your Power.

Cold, dark and damp six am load in for an outdoor rally.  Generator op declares all is ready.  PD is under the back deck of the SL100 stage as there is still a chance of rain.    No one wants to crawl across the wet pavement under the stage so we take a quick look at the tally lights above the cam locks and all looks good.  Start lifting the first array and the 110 VAC half ton motor is unhappy even to run the chain.  Hmmm lets meter the Edison plug.  Whoops 460 VAC.  Turns out the generator op is nothing more than a driver, has no idea what the generator controls do, has never even used his company issue DVM.  Luckily the only casualties are the Motion Labs meter panel and a chain motor and some time spent borrowing a motor from lighting. 

Don't forget to meter your power folks.

Ray Aberle

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Re: Today's cautionary tale
« Reply #1 on: February 25, 2018, 03:57:21 pm »

Damn. I hope you're going to be able to hold the gennie company responsible for the repairs. (And one of the reasons that I appreciate owning a generator-- I know it's going to work, every time.)
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Ivan Beaver

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Re: Today's cautionary tale
« Reply #2 on: February 25, 2018, 08:08:22 pm »

A reminder from the Ministry of Always Meter Your Power.

 Hmmm lets meter the Edison plug.  Whoops 460 VAC. 
Don't forget to meter your power folks.
Long story, but I let a "volunteer who knew what he was doing" tie me in at a school.

Let's just say that a few minutes later he was nowhere to be found, and my ENTIRE system (except speakers), lights and sound was dead.  I had fuse holders blown out of the back of my movers.

He tied me into 460V.

I sent the crew back to the shop to get another system.

We were obviously running late when they got back, and the show was not as good as it should have been (light wise), but it got the job done.

NEVER AGAIN would I trust anybody to tie me in without ME metering it!
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Tim McCulloch

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Re: Today's cautionary tale
« Reply #3 on: February 25, 2018, 08:40:29 pm »

Not so much for Riley but for my memory jog around the block...

From the "back in the day" when all power was "tapped" with 2/0 or 4/0 SO to CamLocks my protocol was:

If possible, meter the LINE side of the switch (not possible with new-ish switch gear) and measure voltage, de-energize switch and measure resistance between neutral & ground.  Tap tails, close box.  Energize switch, close switch, meter voltage at Cams, open switch.  Nowadays many venues have installed CamLock connectors so hard-wiring into lugs isn't as common.  At our PAC we have only 2 services (of a dozen or so) that require bare tails and at the country arena downtown all company switch services are on Cams.  But I digress....

The next step is to WALK the entire feeder run to first distro & verify connections (color code, snugness), then inspect feeder connections to any sub-distros.  Only when all feeder connections are made up and inspected do I then connect the tails to the feeder - if tails are used, close the switch and energize the feeder.  I then meter voltage at the first distro and verify with tour crew before giving them the all-clear to energize their distro.  Ah, the old days. 8) 

With Code compliant company switches these days it is not possible to meter the line side of anything and they typically incorporate shunt trips to de-energize the load side of the switch if a connection chamber (lugs for bare wire tails OR CamLocks) door is open, and some can be fitted to require all Camlocks to fully inserted and snug or the shunt trip will open (there's a long story about WWE, Billy Joel and Elton John that I'll save for another time)...

But metering at the first possible safe place is required and it's essential that NO voltage be applied to branch circuits while doing so (this is where that main breaker in the distro comes into play) and that no down stream sub-distros have circuited loads.

TJ (Tom) Cornish has a well written article on voltage/neutral/ground measurements (linky hint, TJ).

Most of the responses are by folks who already know these things so consider it for those playing along at home.

My near-480V experience was a community festival where the sound genset was bus bar wired for 480V.  I metered the load lugs when they fired it up, turned the breaker off and told them to call the genny shop because re-strapping the bus bars was not in my job description.  Could I have done it?  Probably.  That I'm not 100% certain is already a good reason to not do it, but combined with the "last guy to touch it" liability, hell no.  Get the shop to send a tech.
« Last Edit: February 25, 2018, 08:43:05 pm by Tim McCulloch »
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Mike Sokol

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Re: Today's cautionary tale
« Reply #4 on: February 26, 2018, 06:43:20 am »

A reminder from the Ministry of Always Meter Your Power.

Yes, and that goes double for generator power. Just about every large 3-phase generator I've ever rented can be switched between 208/120 and 480/277 volts and 1-phase vs 3-phase. And one of the local rental houses uses a Japanese brand genny that has no English writing on the controls. Half the time when it's been delivered to my show site it was set for 480/277 and I have to change it. So I never let anyone else test generator power except for me.   
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Chris Hindle

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Re: Today's cautionary tale
« Reply #5 on: February 26, 2018, 01:00:46 pm »

A reminder from the Ministry of Always Meter Your Power.

last century, the "Hotel Guy" at a not-small world famous establishment wired in my 3 phase tails.
Says to me "You're good to go. Have a great show"
He follows me back to the distro, where I pull out a wiggy meter before flipping on the master.
Says to me "Dude, you know what an insult that is?"
I take 2 readings, and he heard the noise that old wiggy made.
Good thing it was rated for 600 volts....
He went white.
"Dude, you got 100K in your pocket for the gear you're going to blow up"

Seems White and Red "found" the wrong lugs, and Green fell off as I moved the feeder for a better view.
Pro's. ya.
At least he had the "decency" to tell his boss not to charge me for the tie-in.
Chris.
Ya know, even with a fresh company switch, I'm STILL going to meter. Every show, no matter how many times I've been there, it still get's metered.
That's CYA 101. No discussion. Just do it.
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Ya, Whatever. Just throw a '57 on it, and get off my stage.

TJ (Tom) Cornish

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Re: Today's cautionary tale
« Reply #6 on: February 26, 2018, 01:11:21 pm »

TJ (Tom) Cornish has a well written article on voltage/neutral/ground measurements (linky hint, TJ).
Receptacle Testing Article
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TJ (Tom) Cornish

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Re: Today's cautionary tale
« Reply #7 on: February 26, 2018, 01:21:25 pm »

Ya know, even with a fresh company switch, I'm STILL going to meter. Every show, no matter how many times I've been there, it still get's metered.
That's CYA 101. No discussion. Just do it.
I had a similar scenario last fall - an event hall room that I had been in before, and a receptacle (14-50) that I had used before.  They had done electrical work in the building since the last time I was there and had wired the neutral wire of the 14-50 to the third hot leg, so I had 208v to ground on both hots and 208v to ground on the neutral.

As to potential gear damage had I not metered - I did an inventory and the only gear on the show that would have been damaged were dimmers and lamp filaments.  Everything else was a universal power supply.  15 years ago nearly everything would have been cooked.  I'm not suggesting that this mitigates the need to test or the potential life safety ramifications, but I found that interesting. 
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Tim McCulloch

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Re: Today's cautionary tale
« Reply #8 on: February 26, 2018, 01:42:34 pm »


Ya know, even with a fresh company switch, I'm STILL going to meter. Every show, no matter how many times I've been there, it still get's metered.
That's CYA 101. No discussion. Just do it.

Yep.  Always.
I had a similar scenario last fall - an event hall room that I had been in before, and a receptacle (14-50) that I had used before.  They had done electrical work in the building since the last time I was there and had wired the neutral wire of the 14-50 to the third hot leg, so I had 208v to ground on both hots and 208v to ground on the neutral.

As to potential gear damage had I not metered - I did an inventory and the only gear on the show that would have been damaged were dimmers and lamp filaments.  Everything else was a universal power supply.  15 years ago nearly everything would have been cooked.  I'm not suggesting that this mitigates the need to test or the potential life safety ramifications, but I found that interesting. 

An unintended consequence of having fewer SKUs, I guess.  But you're right that there is still enough single voltage gear to cripple a show or at least make the day more expensive and complicated.

Best practices exist for a reason and we ignore them at our peril.
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Tom Bourke

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Re: Today's cautionary tale
« Reply #9 on: February 26, 2018, 03:53:02 pm »

last century, the "Hotel Guy" at a not-small world famous establishment wired in my 3 phase tails.
Says to me "You're good to go. Have a great show"
He follows me back to the distro, where I pull out a wiggy meter before flipping on the master.
Says to me "Dude, you know what an insult that is?"
As the Hotel Guy, after I tie some one in I offer "your meter or mine?"  I am in a building that is near 20 years old and we never know if some one went in and made a repair or upgrade.  We have many, very large electrical vaults that most on the crew have no idea even exist.  The staff that maintain the building range from very very good to that one guy I wouldn't let wire up a table lamp.
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Re: Today's cautionary tale
« Reply #9 on: February 26, 2018, 03:53:02 pm »


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