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Author Topic: 3 phase distro carrying hot over to other legs  (Read 2694 times)

Thomas Marshall

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3 phase distro carrying hot over to other legs
« on: May 01, 2015, 03:37:51 am »

Hi,

So I was just doing some organizing and taping what legs carry over to my 50amp and 30amp outs. In the process, I realized I had a ton of voltage crossing over between the hot legs. For testing, I had a 110 drop cord with the ends on it stripped just sitting in the cam ins, I was doing the soley for metering which outputs connect to which legs. There is a volt meter on the top of the distro and if I disconnect it from the voltage sources, the voltage "cross talk" seemed to drop in half but I only tested between a few legs. Attached is an image of the voltages I was getting metered between the cams. The red tape at the top indicates which leg hot the hot wire attached to the cam.

Any ideas why I'm getting this? :/

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Thomas Marshall

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Re: 3 phase distro carrying hot over to other legs
« Reply #1 on: May 01, 2015, 03:39:23 am »

Attached are two more pics and you can see how I was testing the distro
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Michael Ardai, N1IST

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Re: 3 phase distro carrying hot over to other legs
« Reply #2 on: May 01, 2015, 01:47:10 pm »

You are seeing capacitive coupling.  Use a Wiggy or some other meter that presents a load, or stick nightlights (incandescent bulb types) in the Edison outlets (one per phase).

Make sure there's no way for those bare ends to pop out of the cams; otherwise you may be in for a shocking experience
/mike
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Thomas Marshall

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Re: 3 phase distro carrying hot over to other legs
« Reply #3 on: May 01, 2015, 07:18:19 pm »

Ok, thanks!! Does it need to be something with a current as small as night light or can it be a 575watt ellipsoidal? I'll look into purchasing a wiggy too.

Is the capacitive coupling something to be concerned or worried about, or is it somewhat normal?

Is it being induced by the lines bundled together and just noise? Or is it coming from the built in volt meter PCB?

I've used it for a couple shows but just noticed this.
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Mike Sokol

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Re: 3 phase distro carrying hot over to other legs
« Reply #4 on: May 01, 2015, 07:31:59 pm »

Ok, thanks!! Does it need to be something with a current as small as night light or can it be a 575watt ellipsoidal? I'll look into purchasing a wiggy too.

Is the capacitive coupling something to be concerned or worried about, or is it somewhat normal?

Is it being induced by the lines bundled together and just noise? Or is it coming from the built in volt meter PCB?

I've used it for a couple shows but just noticed this.

A night light bulb should be just fine for this test. And I would guess that it's due to capacitive coupling from the lines being bundled close together. Old VOM meters didn't have this ghost voltage problem since they loaded the line to a few hundred k-ohms. But modern DMMs have an input impedance of meg-ohms so the voltage will drift up to whatever it feels like. But the current available is probably in the micro-amps range so it's typically not dangerous. However, if you assume it's a ghost voltage but turns out to be a new low-impedance source, that's when you get into trouble. 
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Mike Sokol
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Scott Holtzman

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Re: 3 phase distro carrying hot over to other legs
« Reply #5 on: May 02, 2015, 03:55:57 am »

Mike - I really don't like those IDC connectors on the metering control panel. 

History has shown they don't survive maintenance.

What do you think?

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Scott AKA "Skyking" Holtzman

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ProSoundWeb Community

Re: 3 phase distro carrying hot over to other legs
« Reply #5 on: May 02, 2015, 03:55:57 am »


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