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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Riley Casey on February 24, 2018, 10:28:58 PM
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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.
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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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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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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.
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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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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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TJ (Tom) Cornish has a well written article on voltage/neutral/ground measurements (linky hint, TJ).
Receptacle Testing Article (http://tjcornish.com/articles/power-and-electricity-artic/receptacle-testing.html)
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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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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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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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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.
Question. Way back I rented a Wacker from a local equipment rental supply company. All I was running was four XTi 4000 amps and my mixer. Outdoor concert with a couple of local bands. Nothing heavy. Recorded music was fine all day. As soon as the band came on I noticed all my amps were showing red like they were clipping and had low sound output. I was panicked as it was my first outdoor event and generator event. I knew something was wrong on the gen but I had to stay and work with what I had as the band was live. I just had no experience with generators and figured since I explained what it was for the rental place would have it ready to go. I used my own 6/4 cable and distro (those checked out OK). I posted this years ago in the Lab and people seemed to think the voltage was set too low since the XTis were known to go into that mode under those conditions. But could it have been 480/277? If it was, I suppose the amps would not have worked even for house music?
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Question. Way back I rented a Wacker from a local equipment rental supply company. All I was running was four XTi 4000 amps and my mixer. Outdoor concert with a couple of local bands. Nothing heavy. Recorded music was fine all day. As soon as the band came on I noticed all my amps were showing red like they were clipping and had low sound output. I was panicked as it was my first outdoor event and generator event. I knew something was wrong on the gen but I had to stay and work with what I had as the band was live. I just had no experience with generators and figured since I explained what it was for the rental place would have it ready to go. I used my own 6/4 cable and distro (those checked out OK). I posted this years ago in the Lab and people seemed to think the voltage was set too low since the XTis were known to go into that mode under those conditions. But could it have been 480/277? If it was, I suppose the amps would not have worked even for house music?
480/277 would almost certainly have meant smoke. Low voltage would be more likely to cause the issues you indicate.
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480/277 would almost certainly have meant smoke. Low voltage would be more likely to cause the issues you indicate.
No smoke! Thanks. Lesson learned.
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A brand new, never used before, 70KVA generator (name brand but a model I hadn't worked with) was provided by the city for my outdoor event. We were setting the stage up the day before the event and wanted to unfold and raise the roof on my portable hydraulic stage. I had checked that we had three legs of 120V and ground and neutral were good. With the roof in its down position, we unfolded the front and back roof panels so the front and rear stage sections could fold down. It takes a few minutes to get all of the legs in place and the stage leveled, and during this time we guess the generator decided to go into a "protect itself" mode for some reason with almost no load on it. The only thing running was that 2HP hydraulic pump which was just idling with no load. This "protect" mode drops the output voltage of the generator to about 40 volts, which caused the starting coil on my hydraulic pump motor to fail! The motor turns but with no usable power. We are in a fairly small town and it's Friday night at 7PM with an 11AM Saturday start time. The two local motor distributors did return my calls to their emergency numbers, but didn't have the motor I needed. Hitting every hardware store, auto parts store, lumber yard, and farm & ranch supply at 7AM the next morning yielded enough jacks and support blocks to safely raise to roof about three and one-half feet of its usual additional 8' before the band arrived. The show only started about 5 minutes late. The closest new motor I could find was four states away and the 2 day air freight (needed for my next event) was over $350.00. I purchased and now have a spare motor. Restarting the generator solved its "emergency", but not mine!
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Receptacle Testing Article (http://tjcornish.com/articles/power-and-electricity-artic/receptacle-testing.html)
Thank you for re-posting this concise and well written testing procedure!
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As for something that actually looks like it was done by a real profession was a function room in a local theatre, each socket had a coloured plate below it identifying the phase it was on and warning that it had 415V between it and any other socket, something simple but at the same time nice to see, some other sockets in the place are coloured to denote phase also.
But then again there seems to be higher general standards of wiring in the UK to what this forum has exposed to me of the US.
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As for something that actually looks like it was done by a real profession was a function room in a local theatre, each socket had a coloured plate below it identifying the phase it was on and warning that it had 415V between it and any other socket, something simple but at the same time nice to see, some other sockets in the place are coloured to denote phase also.
But then again there seems to be higher general standards of wiring in the UK to what this forum has exposed to me of the US.
There are voltage-specific color schemes and labeling conventions that should be followed. Most of the trouble comes from the fact that people screw up - electricians moving things; generator "ops" that don't know how to operate the generator and set it correctly for the load, etc. The National Electric Code uses the term "qualified personnel" in a number of places. Those people are not always available when needed.
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I think every generator that's ever been delivered to me has been set wrong, and the techs or electricians never seem to be able to figure out what I need. I can tell them to their face that I need 208v 3-phase and they'll still set it to 240 single phase or something. Yeah, that's why I gave you 5-wire tails, because I want 240. Or they can't understand why 480 won't work. It's more efficient, so it's got to be better, right? You know what, guy, just pound the ground rod in for me and I'll do the rest. I know how to work a socket wrench just as well as you do.
I never trust a generator unless I verify that it's set correctly and meter it myself. There's too much at stake to trust someone who doesn't get it.
Also, I hate the new computer controlled generators. There's too many "features" that can take down my show. Give me an old school, low-tech, rock-solid genny every time and I'll be happy.
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Yep, I ran into a similar situation again just now. Two 120v circuits/receptacles meter just fine, but a third metered at 213v. Always check the power before plugging in!
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Yep, I ran into a similar situation again just now. Two 120v circuits/receptacles meter just fine, but a third metered at 213v. Always check the power before plugging in!
True that!!!
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Yep, I ran into a similar situation again just now. Two 120v circuits/receptacles meter just fine, but a third metered at 213v. Always check the power before plugging in!
Jeff, it sounds like you have what was explained to me as "wild leg" three phase. I'm not making that up. In my home town, the third leg usually measures a full 240 volts. This is in our "older" downtown area with most of the major buildings built in the 1950's. 3 phase motors run reasonably well (at least without problems-yet), but it can kill audio gear! Be afraid. Be very afraid!
As has been stated by others, 120/208 three phase confuses a lot of generator suppliers. I've had generator suppliers come in early in the mornings of multi-day events, and not only refuel the gen set, but "correct" my 3 phase settings by changing it to single phase, and once even to 460V. I check BEFORE I fire it up and before I turn on the main breaker!
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Yep, I ran into a similar situation again just now. Two 120v circuits/receptacles meter just fine, but a third metered at 213v. Always check the power before plugging in!
Yeah, i got this exact thing last genie i worked with.
Gotta meter ALL the things...
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Yeah, i got this exact thing last genie i worked with.
Gotta meter ALL the things...
We've covered this before, but it's always good to revisit a topic that's potentially so dangerous. High-Leg Delta service was often brought into industrial buildings that needed mostly 3-phase motor power that didn't even require a neutral. But you could get 120/240-volts off of the lower pair of legs on the center-tapped winding. What really grinds me is electricians hooking into the High (or Wild) Leg, and never use a meter to confirm the correct voltage.
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We've covered this before, but it's always good to revisit a topic that's potentially so dangerous. High-Leg Delta service was often brought into industrial buildings that needed mostly 3-phase motor power that didn't even require a neutral. But you could get 120/240-volts off of the lower pair of legs on the center-tapped winding. What really grinds me is electricians hooking into the High (or Wild) Leg, and never use a meter to confirm the correct voltage.
This is exactly what I suspect happened. This is a newly installed power box (the kind you find at venues for bus/RV/trailer hookup). The two 5-20Rs are 120v as advertised, the 14-50R meters 240/120 as expected, but the TT-30R came in at 213v when it should have been 120v. I'm very involved with this particular project and know the electrician had to install this equipment prior to the utility service being connected (hence he couldn't test this himself). Good thing I did! I ensured the whole box was de-energized and locked out/tagged out until the electrician could return to correct the problem. You just can't be too careful with these things!
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The NEC requires "high legs" to be marked with orange (orange is also used in 480/277 panels). If you ever see orange in a 208/240 panel it should raise a red flag.
The other place "high" or wild leg services are found are in places that are mainly 120 volt loads, but need or want 3 phase for AC/air handling. The POCO can do a wild leg with 2 transformers instead of 3, saving them money (sometimes cost that is passed on to the customer at the time of install-so its not always the POCO being cheap).
One of the odd/annoying things is that POCO's don't play by the NEC-they use the NESC. In my area, the POCO uses blue/yellow/red to mark 480-electricians use brown/orange/yellow. The NEC requires high leg to be "B" phase, I think the POCO usually runs their equipment with it on the "C" phase. Obviously an easy place for a mistake/miscommunication to happen.