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Author Topic: And then sparks flew  (Read 4887 times)

Theo_Christofore

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And then sparks flew
« on: July 03, 2015, 10:05:48 am »

Hi guys!

My partner recently shared a pretty scary story about a gig we had recently. I wasn't actually there to provide you with full details on what happened, but here is what I do know.
 Dubuque, IA at the Grand River Center. Pretty nice convention facility, and this would be the second time we have been there for this particular show.
 We knew that they have 50amp - hubbel marine style receptacles in their floor pockets. We planned accordingly: 4/4 wire with the 50amp marine plug > to 4 wire cam tail. The cams will feed our distro (ampshop.com) which then flows through to our dimmer rack via 50amp cali plug.

 Main breaker of the distro is in the OFF position, but the indicator light is showing current.
 He flips the main, and starts to meter through the tiny holes above the cam receptacles.
 Ground to neutral - zeros
 Ground to hot number 1 - and POP.. sparks fly

 They step back to examine what happened, shut it down and went to double check the wiring on the plug, since he had just tied the bare ends to it that day. The plug was wired properly, so he re-connected it a second time, and everything metered correctly with no modification.


 Could this be something going on inside my distro?
 I know the floor pockets had a 208, and a 120 receptacle, but I thought I remember them being slightly different connectors. So I don't think he accidentally used the wrong receptacle.



 Any thoughts on this?
 I will be riding up with him to a gig this afternoon, so if you had any detailed questions about the scenario, I would be happy to ask him.
 Like I said, I wasn't there. But Its equipment that we share, so I was a bit concerned when he told me what happened.


 Thanks for reading!
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Stephen Swaffer

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Re: And then sparks flew
« Reply #1 on: July 03, 2015, 11:08:54 am »

It could be anything-depends on where sparks flew.  "Brand new" connections are always suspect-it is a good idea to verify continuity/separation of conductors with an ohmmeter before applying power-though that step is often skipped.  My guess is a stray strand of wire that moved ever so slightly as he probed with the meter leads.  It would likely have fused and vaporized-so re applying power everything seems normal-but you still might have hairsbreadth clearance between energized parts just waiting for the best (IE most inconvenient) time to renew the spark.  Best to go over with a fine tooth comb.
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Steve Swaffer

frank kayser

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Re: And then sparks flew
« Reply #2 on: July 03, 2015, 01:56:07 pm »

That was my first guess... 
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Theo_Christofore

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Re: And then sparks flew
« Reply #3 on: July 03, 2015, 02:12:03 pm »

There wouldn't have been any stray wiring inside the connector.
The marine plug is huge and the 4 gauge wire fits all the way into the large  holes before being tightened.
Also the holes are pretty far apart, so it's highly unlikely that anything was touching.

The spark happened on the front panel of the distro right when he inserted the meter on the first hot.
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Jonathan Johnson

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Re: And then sparks flew
« Reply #4 on: July 04, 2015, 01:28:07 am »

The meter was on current, not voltage?
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Theo_Christofore

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Re: And then sparks flew
« Reply #5 on: July 05, 2015, 01:38:13 pm »

The meter was on current, not voltage?

He does claim the meter was set to voltage (200)
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TJ (Tom) Cornish

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Re: And then sparks flew
« Reply #6 on: July 05, 2015, 06:35:50 pm »

He does claim the meter was set to voltage (200)
Where the knob is is only half the story. Where were the probes plugged in on the meter?  If the probes were in the amperage jacks, the meter is effectively a dead short and would definitely make some sparks until the meter's fuse blew.
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Mike Sokol

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Re: And then sparks flew
« Reply #7 on: July 05, 2015, 08:24:14 pm »

Where the knob is is only half the story. Where were the probes plugged in on the meter?  If the probes were in the amperage jacks, the meter is effectively a dead short and would definitely make some sparks until the meter's fuse blew.
So there's only two real possibilities that can explain the fireworks. Either the meter presented a low-resistance across the probes, such as plugging the probes into the 10-amp current jacks, or somehow the sparking meter probe bridged between a hot and ground or neutral connection. As noted, the 10-amp jacks on the meter would be fused, so if that didn't blow, then the probe tip must have bridged something. Were there any burn marks on the face of the connector? 
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Jonathan Johnson

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Re: And then sparks flew
« Reply #8 on: July 07, 2015, 01:50:20 am »

So there's only two real possibilities that can explain the fireworks. Either the meter presented a low-resistance across the probes, such as plugging the probes into the 10-amp current jacks, or somehow the sparking meter probe bridged between a hot and ground or neutral connection. As noted, the 10-amp jacks on the meter would be fused, so if that didn't blow, then the probe tip must have bridged something. Were there any burn marks on the face of the connector?

Not all meters are fused on the 10-amp jacks. Or maybe I should say unfused meters will become the fuse?

(Anybody find it ironic that the verb fuse means to join while the noun fuse is something that separates?)
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Frank DeWitt

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Re: And then sparks flew
« Reply #9 on: July 07, 2015, 02:00:57 pm »

(Anybody find it ironic that the verb fuse means to join while the noun fuse is something that separates?)

So if you don't have a fuse then the parts will be fused together.  We have a strange language. I just parked my car in the driveway after a long drive on the parkway.  When we left my wife told me it was OK to go ahead and back up before saying turn left right here.
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Jonathan Johnson

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Re: And then sparks flew
« Reply #10 on: July 08, 2015, 01:38:05 pm »

So if you don't have a fuse then the parts will be fused together.  We have a strange language. I just parked my car in the driveway after a long drive on the parkway.  When we left my wife told me it was OK to go ahead and back up before saying turn left right here.

The opposite of left is right. The opposite of right is wrong. Therefore, those on the left are wrong.  :o

(Not entirely off-topic, because that statement will likely make sparks fly!)
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David Allred

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Re: And then sparks flew
« Reply #11 on: July 08, 2015, 03:20:24 pm »

The opposite of left is right. The opposite of right is wrong. Therefore, those on the left are wrong.  :o

(Not entirely off-topic, because that statement will likely make sparks fly!)

Good thing this is not in the Basement or you could be in trouble.
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ProSoundWeb Community

Re: And then sparks flew
« Reply #11 on: July 08, 2015, 03:20:24 pm »


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