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Author Topic: Just a reminder to check the power at your distro as well as the wall.  (Read 21133 times)

Tom Bourke

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Was working as an electrician on a show today.  Tied in several distros.  Then they had me add a small distro via the cam outs of one already tied in that I had not done.  Hooked it all up and then metered the test points on the new distro.  Ground was floating!  Checked the original distro and it was good.  Went to check the cams and the end came off the feeder cable!
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I have a mild form of Dyslexia that affects my ability to spell.  I do use spell checking to help but it does not always work.  My form of Dyslexia does not affect my reading.  Dyslexics of the world untie! <a href="http://www.cwalv.com" target="_blank">http://www.cwalv.com</a>

Steve M Smith

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #1 on: January 26, 2014, 03:31:15 am »

Went to check the cams and the end came off the feeder cable!

Sorry, it's probably just me being English and not aware of the term but what do you mean by cam?  We probably call it something else.


Steve.
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Tim McCulloch

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #2 on: January 26, 2014, 07:31:40 am »

Sorry, it's probably just me being English and not aware of the term but what do you mean by cam?  We probably call it something else.


Steve.

Cam-Lok®.  A trademarked name for a single pole, separable connector.

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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Mike Sokol

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #3 on: January 26, 2014, 09:29:29 am »

Was working as an electrician on a show today.  Tied in several distros.  Then they had me add a small distro via the cam outs of one already tied in that I had not done.  Hooked it all up and then metered the test points on the new distro.  Ground was floating!  Checked the original distro and it was good.  Went to check the cams and the end came off the feeder cable!

+1 on this... I know I'm paranoid, but am I paranoid enough? Cam-Locks take a lot of abuse dragging them around, so never trust anything. As a final test for back-line grounds I like to poke a NCVT at a few microphones (just one should be sufficient) and all stage amps or DI'ed instruments (musicians  are notorious for cutting off the ground prongs on their power cords). Generally any open grounds will allow the gear chassis to float up to at least 1/2 of line voltage (120/60 volts in the USA and 230/115 volts in the UK). While many of these chassis voltages will be low-current (less than a few mA), some will have much higher potential fault currents (1 to 20 amps) with 120-volts on the mics or stage amp chassis, and thus be VERY dangerous to performers and technicians.   

Every NCVT (Non Contact Voltage Tester) that I've reviewed, that was rated for 90 to 600/1,000 volts, will trigger on a large surface charged with as little as 40 volts or so. You can purchase a NCVT at any big-box store or online for $15 to $25. A standard sensitivity NCVT is also useful for testing receptacles (outlets) for proper H-N polarity. While generally not an immediate danger, a swapped Hot and Neutral hints that the wiring was done incorrectly and could have other (more dangerous) problems. Here's a video I did for RVtravel on how to use a NCVT to check outlet H-N polarity, but it's exactly the same procedure for testing back-line outlets: http://www.youtube.com/watch?v=jF3Ntoa8ab8
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Tom Bourke

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #4 on: January 26, 2014, 10:17:44 am »

Lately I have been carrying a pair of Fluke NCVT's.  One fits on my key-ring and has dual voltage (via two colors) and a flashlight.  The other is the full size 90 to 1000V unit.  I find them to be great time savers in trouble shooting lighting rigs. It is almost like you can look into the cables and see power.  You still need a full meter, but not as often.  Had one instance of a 220V adapter wired with the same phase on each line.  Tested as it should with the noncontact.  However 120V to ground on each and 0 volts phase to phase was the giveaway.  It was an interesting day.
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I have a mild form of Dyslexia that affects my ability to spell.  I do use spell checking to help but it does not always work.  My form of Dyslexia does not affect my reading.  Dyslexics of the world untie! <a href="http://www.cwalv.com" target="_blank">http://www.cwalv.com</a>

Mike Sokol

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #5 on: January 26, 2014, 10:35:19 am »

Lately I have been carrying a pair of Fluke NCVT's.  One fits on my key-ring and has dual voltage (via two colors) and a flashlight.  The other is the full size 90 to 1000V unit.  I find them to be great time savers in trouble shooting lighting rigs. It is almost like you can look into the cables and see power.  You still need a full meter, but not as often.  Had one instance of a 220V adapter wired with the same phase on each line.  Tested as it should with the noncontact.  However 120V to ground on each and 0 volts phase to phase was the giveaway.  It was an interesting day.

Of course a NCVT is not a substitute for a good voltmeter. But you are correct that it's a great tool that can help you speed up troubleshooting. The key is to use all your test gear enough to know when something just doesn't add up. I teach my basic electronics students to predict what voltage they should measure BEFORE they turn on a meter and stick in the probes. And then we discuss the implications of getting various unpredicted meter readings.

As the OP noted, it's best to measure twice and avoid getting shocked once (or something like that)...
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frank kayser

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #6 on: January 26, 2014, 02:46:06 pm »

Was working as an electrician on a show today.  Tied in several distros.  Then they had me add a small distro via the cam outs of one already tied in that I had not done.  Hooked it all up and then metered the test points on the new distro.  Ground was floating!  Checked the original distro and it was good.  Went to check the cams and the end came off the feeder cable!

I have no idea of how these connectors work, so please bear with me.  Just to clarify for me, are you stating the cam connector was still connected, but the wire had slipped out and was bare?
Is a simple yank on the wire/connector sufficient before connecting (by proper electrician).  If I owned the cables, what would be sufficient maintenance or test of these cables?
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Tom Bourke

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #7 on: January 26, 2014, 03:31:43 pm »

I have no idea of how these connectors work, so please bear with me.  Just to clarify for me, are you stating the cam connector was still connected, but the wire had slipped out and was bare?
Is a simple yank on the wire/connector sufficient before connecting (by proper electrician).  If I owned the cables, what would be sufficient maintenance or test of these cables?
Yes, the cable came out of the connector so I had a bare end of copper cable.  In this case it was a ground going to a distro with nothing on it yet so the danger was minimal.  However if I had not discovered it, then a failure of something else plugged into it could have caused a piece of equipment or even a metal support to become “live.”

As for a proper check, I should have given a tug on each end before mating it.  In use, a loose end on a current carrying line will cause heat at the connector.  The venue had one of the disconnects locked out because some one melted a line out of it.  I should have taken a pic. The scary part is that so much of the equipment we use is just rental and the people using it may not know any better.  Then when a problem is discovered it may or may not get marked.  If it is marked you can only hope the person who finds it in the shop does something about it.
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I have a mild form of Dyslexia that affects my ability to spell.  I do use spell checking to help but it does not always work.  My form of Dyslexia does not affect my reading.  Dyslexics of the world untie! <a href="http://www.cwalv.com" target="_blank">http://www.cwalv.com</a>

Steve M Smith

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #8 on: January 26, 2014, 03:58:09 pm »

I have no idea of how these connectors work

Neither do I.  If they are just a single conductor, how are they used?  And what prevents you from connecting them to the wrong place?

EDIT:  Just found this:


That seems like a crazy way to connect things.

We would use one of these:



Steve.
« Last Edit: January 26, 2014, 04:04:35 pm by Steve M Smith »
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Mike Sokol

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Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #9 on: January 26, 2014, 04:03:21 pm »

Neither do I.  If they are just a single conductor, how are they used?  And what prevents you from connecting them to the wrong place?

EDIT:  Just found this:

That seems like a crazy way to connect things.

Steve.

Yup, the colors are the only thing keeping you from making a mistake...

And NEVER pull the Neutral Cam while the circuit breaker is on and you're sending power to things. VERY BAD things will happen... I actually saw someone getting ready to do that on a gig to tie lighting into the third phase of a big generator, and I screamed and slapped his hand away.
« Last Edit: January 26, 2014, 04:36:02 pm by Mike Sokol »
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Mike Sokol
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ProSoundWeb Community

Re: Just a reminder to check the power at your distro as well as the wall.
« Reply #9 on: January 26, 2014, 04:03:21 pm »


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