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Author Topic: Meter and test every show  (Read 9922 times)

Kemper Watson

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Meter and test every show
« on: October 13, 2013, 11:50:46 am »

Provided for a show yesterday in North Atlanta.. Stage and generator are provided by the same guy every year and I noticed he had brand new spider boxes and cabling. Just out of curiosity I metered the outlets. All was fine. Then I plugged in the polarity checker. There was a hot-neutral swap somewhere. He took apart the BRAND NEW California connectors and found not only a miswired connector but a messy job as well. He spent an hour taking apart and reconnecting his cables.. Meter and check every show..
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Mike Sokol

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Re: Meter and test every show
« Reply #1 on: October 14, 2013, 08:47:52 am »

Meter and check every show..

I agree 100%. It only takes a few minutes to meter the power, and that can save you thousands of dollars in electrical damage. For instance, I did a seminar a few years back in a gymnasium at a big church, and was told to plug in my PA and video system anywhere. Well, I found a brand new receptacle on the back of the stage which was close to my rack, so I simply plugged in. My rack had a Furman power distro feeding most of the gear, but I had recently added an extra wireless mic receiver and didn't have enough outlets on the Furman distro, so I foolishly put a power strip on the floor BEFORE the rack and plugged in the extra RF receiver. When I plugged into the outlet, I noticed two things. The Sennheiser RF receiver display got VERY BRIGHT for a few seconds and then went out. And the voltage monitor bar on the Furman distro was pegged to the right. That prevented me from flipping on the power to the rest of the rack. I then metered the stage outlet and found what appeared to be a standard 15-amp 120-volt Edison receptacle had 240-volts on it. When I complained to the church maintenance guy, he said I must have plugged into the "special outlet" he had rewired to 240-volts for the floor buffer. Yikes!!! Of course it's a code violation to wire any 120-volt outlet to 240-volts, and certainly crazy not to mark it as 240-volts. But there it was, and it blew up a $1,000 receiver in seconds. After that, I began checking voltage and grounding at all new sites I work, especially when there's a new outlet in and old building. That's a danger sign especially in a church since a lot of volunteers and maintenance guys do these outlet "upgrades" and often don't understand the electrical code or how to measure voltage. 
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Frank Koenig

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Re: Meter and test every show
« Reply #2 on: October 14, 2013, 10:37:48 am »

Metering power before plugging in is like checking the fuel quantity on an airplane before departure. Just do it, even if you "know" it's OK.

I have an observation on using a regular volt meter, as opposed to a non-contact "AC voltage checker", for verifying that grounds are not hot. I do not suggest that anyone do this as a matter of course, as it's a little non-standard and potentially hazardous, and put it out here for the amusement of folks who have more of an experimental mind set when it comes to electricity.

Get up on your rubber soles and grab one probe of the meter. You have now become a capacitively-coupled ground reference to the universe (or at least your immediate vicinity). The other probe can now be used to check that equipment grounding conductors and grounded circuit conductors are grounded, and that hots are hot. If your meter is healthy you're connecting yourself to the line through a 10 M Ohm resister, so you won't die, even if you're grounded. (Hell, you won't even trip the GFI.) The reason for getting up on your soles is in case the meter is internally shorted or you plugged the leads into the current hole by mistake.

Actually, you could make up a special lead with a, say, 10 M Ohm, high-voltage resistor in series. With triple redundancy (meter, external resistor, and dry rubber soles) this would be pretty safe.

Like I said, only by qualified personnel, laboratory use only, etc.

--Frank
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Mike Sokol

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Re: Meter and test every show
« Reply #3 on: October 14, 2013, 11:03:26 am »


Get up on your rubber soles and grab one probe of the meter. You have now become a capacitively-coupled ground reference to the universe (or at least your immediate vicinity). The other probe can now be used to check that equipment grounding conductors and grounded circuit conductors are grounded, and that hots are hot. If your meter is healthy you're connecting yourself to the line through a 10 M Ohm resister, so you won't die, even if you're grounded. (Hell, you won't even trip the GFI.) The reason for getting up on your soles is in case the meter is internally shorted or you plugged the leads into the current hole by mistake.

--Frank

While this does work, and we used to do this with a neon bulb back in the "old days", I think it's way too dangerous for the casual user (as you note in your post). Just spend the $20 and get a NCVT such as a Klein NCVT-1 or Fluke VoltAlert. I'm also an advocate for using a NCVT on a newly wired stage as a quick hot-ground check on backline guitar amps and such. Simply walk around the powered-up stage with your NCVT and touch the microphones and guitar/stage amps. If it lights up and beeps, that's the warning sign that something is not grounded properly. I've had my microphones blamed for shocking the guitar players, when in fact he had an old amp he just bought at a pawn shop without a ground pin on the plug, and he was getting shocked from his amp. But because he felt the shock on his lips, the mic (and my sound system) was blamed for the shock.

Many years ago I had the fun ??? of doing sound for Chumbawumba on the roof of a garage in Wash DC. This was an unlicensed event that supposed to get them arrested as a publicity stunt. Getting more fun, isn't it. Well there was a contractor generator down on the ground feeding our power distro up on the roof, and while metering the power I measured 90 volts between the "ground" of the PA system on the roof, and the "grounded" safety rail around the roof. Of course, we had built a stage to get the band up to the level of the safety rail, and I was worried that a guitar player getting a shock between his guitar and the rail might take a plunge off the roof to the street some 40 feet below. A little too much publicity for my taste, so I did some troubleshooting and found that the generator down on the ground didn't have a ground rod. Running out of time before the show, I found a piece of rebar, drove it into the dirt next to the generator, and used a pair of vise grip pliers to bond it to the generator frame with a short run of heavy wire. Yes, I taped the vice grip handle to make sure it didn't shake loose, and it properly eliminated the hot ground on the stage up above. But without metering the power distro, I could have been involved in something very bad with potential litigation. I ALWAYS test outside stages with generators for proper grounding. Too many things to go wrong otherwise.
« Last Edit: October 14, 2013, 11:18:45 am by Mike Sokol »
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John Roberts {JR}

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Re: Meter and test every show
« Reply #4 on: October 14, 2013, 11:43:52 am »

Metering power before plugging in is like checking the fuel quantity on an airplane before departure. Just do it, even if you "know" it's OK.

I have an observation on using a regular volt meter, as opposed to a non-contact "AC voltage checker", for verifying that grounds are not hot. I do not suggest that anyone do this as a matter of course, as it's a little non-standard and potentially hazardous, and put it out here for the amusement of folks who have more of an experimental mind set when it comes to electricity.

Get up on your rubber soles and grab one probe of the meter. You have now become a capacitively-coupled ground reference to the universe (or at least your immediate vicinity). The other probe can now be used to check that equipment grounding conductors and grounded circuit conductors are grounded, and that hots are hot. If your meter is healthy you're connecting yourself to the line through a 10 M Ohm resister, so you won't die, even if you're grounded. (Hell, you won't even trip the GFI.) The reason for getting up on your soles is in case the meter is internally shorted or you plugged the leads into the current hole by mistake.

Actually, you could make up a special lead with a, say, 10 M Ohm, high-voltage resistor in series. With triple redundancy (meter, external resistor, and dry rubber soles) this would be pretty safe.

Like I said, only by qualified personnel, laboratory use only, etc.

--Frank
This needs a strong "don't try this yourself' disclaimer.

I have done this myself and it kind of works, but on a public forum how can we be sure that the users will remember to only use voltage measurement ranges that should safely limit current to modest levels. There are too many ways to use a VOM that are not current limited to low mA levels. 

So do not do this,,,

Frank knows his way around test equipment and electricity, but another data point from last time I did some research into who actually gets electrocuted. A disproportionate number of deaths are engineers. technicians, and electrical professionals who should know better. Sometimes we get a little blasť about the risks.

JR 
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Mike Sokol

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Re: Meter and test every show
« Reply #5 on: October 14, 2013, 12:00:27 pm »

This needs a strong "don't try this yourself' disclaimer.

I have done this myself and it kind of works, but on a public forum how can we be sure that the users will remember to only use voltage measurement ranges that should safely limit current to modest levels. There are too many ways to use a VOM that are not current limited to low mA levels. 

So do not do this,,,

Frank knows his way around test equipment and electricity, but another data point from last time I did some research into who actually gets electrocuted. A disproportionate number of deaths are engineers. technicians, and electrical professionals who should know better. Sometimes we get a little blasť about the risks.

JR

Yup... DO NOT DO THIS!!! It's way too dangerous and an unnecessary risk.

We "professionals" do get too casual around live voltage. When I was a young electrical engineer working for a major glass manufacturer, there was an EE in another plant (basically doing the same job as me) who was discussing a problem with management about how an electrician had received a shock from a live 11,000 volt panel because he hadn't tested his gloves properly. The electrician lived, but the engineer didn't because as part of his demonstration to the plant manager he poked the live 11,000 volt bus with a pencil. Of course, graphite is conductive and it killed the engineer on the spot. I got really serious about live electrical panels after that incident.

That's also why I don't let anybody talk to me or distract me in any way when I'm working in a live panel out of necessity. I hate doing that, but sometimes it's the only way to get the job done. However, I then take extra safety precautions including having somebody with a cell phone close by who can call 911 and start CPR if something goes wrong. And I always use my PPE (Personal Protection Equipment). Safety glasses have saved my eyesight on more than one occasion.

There are OLD electricians and BOLD electricians, but very few OLD and BOLD electricians.
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Tim McCulloch

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Re: Meter and test every show
« Reply #6 on: October 14, 2013, 12:07:01 pm »

Mike, how about a little detour (new topic) on arc flash and PPE?
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Frank Koenig

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Re: Meter and test every show
« Reply #7 on: October 14, 2013, 02:11:28 pm »

A disproportionate number of deaths are engineers. technicians, and electrical professionals who should know better.

Wise words. I wasn't trying to cause trouble, just generate a little discussion and thinking. And I'm going to get  one of those NCVTs for my kit. -F
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Jamin Lynch

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Re: Meter and test every show
« Reply #8 on: October 14, 2013, 03:51:42 pm »

Provided for a show yesterday in North Atlanta.. Stage and generator are provided by the same guy every year and I noticed he had brand new spider boxes and cabling. Just out of curiosity I metered the outlets. All was fine. Then I plugged in the polarity checker. There was a hot-neutral swap somewhere. He took apart the BRAND NEW California connectors and found not only a miswired connector but a messy job as well. He spent an hour taking apart and reconnecting his cables.. Meter and check every show..

HHMMM? Did a licensed electrician change out the wiring or just the guy who brought out the generator? You're gonna burn the place down.
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Kemper Watson

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Re: Meter and test every show
« Reply #9 on: October 14, 2013, 04:21:07 pm »

HHMMM? Did a licensed electrician change out the wiring or just the guy who brought out the generator? You're gonna burn the place down.

It was the owner of the generator, not "some guy that brought the genny" He went through all the BRAND NEW cables he bought and straightened  the problem out.

Edit: He bought the cables from a new distributor somewhere on line. I had never had a problem with his distro's ever, in 6-7 years of working with him..Stand up guy. He will never NOT check brand new cables again..
« Last Edit: October 14, 2013, 04:26:33 pm by Kemper Watson »
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