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Author Topic: Help trouble shoot speaker voltage leak.  (Read 5341 times)

Steve M Smith

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Re: Help trouble shoot speaker voltage leak.
« Reply #10 on: November 01, 2015, 03:41:49 am »

Refresh my memory, but India uses British power voltages and pin-outs, correct. That is, 230 volts at 60 Hz

50Hz.


Steve.
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Nitin Sidhu

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Re: Help trouble shoot speaker voltage leak.
« Reply #11 on: November 01, 2015, 04:12:29 am »

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Mike Sokol

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Re: Help trouble shoot speaker voltage leak.
« Reply #12 on: November 01, 2015, 06:56:27 am »

We measure to ensure that the Hot-Neutral wires are not swapped. So...

You really need to measure ground-to-ground for each of the outlets and check for any voltage. I take a basic 100 ft extension cord with me and run it from the console power outlet up to the stage. Then I drag the end of the extension cord over to each stage outlet and meter between the ground of the extension cord and ground of the stage outlet. Anything more than 1/10th of the volt can cause ground loop hum for gear with the "pin-1 problem". If you measure around 1/2 of line voltage (60 volts in the USA and 100-ish volts in your venue) then there's probably a floating ground wire. If you measure full line voltage (120 in the USA and 240 elsewhere) then there's a direct connection between the hot and ground wires. If this is a true RPBG then connecting a 100 watt light bulb between the two "grounds" will have the bulb light up at full brightness. A true RPBG will have full circuit breaker current available so you could even light a 1,000 watt PAR light connected ground-to-ground. That's what makes it so scary.

Do not assume that your hot and neutral wires aren't reversed unless you measure it yourself. And has JJ hinted, you must have an external source to measure against. I used to run a test wire to a copper water pipe for measurements, but now that there's so much PVC pipe that doesn't work very well. So running a test wire back to the service panel ground is the best way to test outlets if you can manage it. 
« Last Edit: November 01, 2015, 06:59:34 am by Mike Sokol »
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Geoff Doane

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Re: Help trouble shoot speaker voltage leak.
« Reply #13 on: November 02, 2015, 11:38:59 am »

I know you mentioned that you have a good ground, but it sounds a lot like the venues' grounds are not actually connected to anything and are floating.  The capacitance in the windings of the speaker's power transformer will cause its chassis to float up to about half the line voltage, in your case, 100V.  There shouldn't be very much current available, but the high static voltage might be able to destroy output circuits connected to it.

GTD
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Mac Kerr

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Re: Help trouble shoot speaker voltage leak.
« Reply #14 on: November 02, 2015, 12:22:33 pm »

I know you mentioned that you have a good ground, but it sounds a lot like the venues' grounds are not actually connected to anything and are floating.  The capacitance in the windings of the speaker's power transformer will cause its chassis to float up to about half the line voltage, in your case, 100V.  There shouldn't be very much current available, but the high static voltage might be able to destroy output circuits connected to it.

And hopefully by now you understand that a ground rod or a cold water pipe is not a ground for electrical safety or circuit protection. That demands a ground safety wire run from the outlet back to the service panel to provide an alternate path for fault current to reach the breaker and blow it.

Mac
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Jonathan Johnson

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Re: Help trouble shoot speaker voltage leak.
« Reply #15 on: November 02, 2015, 12:39:02 pm »

And hopefully by now you understand that a ground rod or a cold water pipe is not a ground for electrical safety or circuit protection. That demands a ground safety wire run from the outlet back to the service panel to provide an alternate path for fault current to reach the breaker and blow it.

Mac

To expand on Mac's point, the equipment grounding conductor (EGC) must be bonded to the grounding electrode conductor (GEC; leads to the earth ground point such as a ground rod, concrete-encased rebar, or metallic underground water line) AND the neutral conductor in the service entrance. This should be the ONLY point of common bond between ground and neutral on the customer side of the utility meter.

Without this ground/neutral bond, there is no reliable return path to trip a circuit breaker or GFI. It might be argued without the bond, the system is floating, but that's not reliable either because in some utility distribution scenarios (such as is common in the United States), all secondary neutrals -- even ones from different utility transformers -- are bonded together and to ground. So while you may be missing the ground/neutral bond in your service entrance, there may be one at the utility transformer or even at your neighbor's utility transformer. So there will be a return path of some sort, though it might be high-resistance. If the resistance of that return path is higher than the resistance of the return path through a human body or through equipment, bad things can happen.
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Nitin Sidhu

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Re: Help trouble shoot speaker voltage leak.
« Reply #16 on: November 02, 2015, 02:33:58 pm »

I know you mentioned that you have a good ground, but it sounds a lot like the venues' grounds are not actually connected to anything and are floating. 

By good ground I mean a Ground-Live measurement that is within a couple of volts of the L-N difference. If the ground is floating, I have seen we measure a voltage in the Ground wire using a voltage tester..
« Last Edit: November 03, 2015, 02:05:32 am by Nitin Sidhu »
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Mike Sokol

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Re: Help trouble shoot speaker voltage leak.
« Reply #17 on: November 02, 2015, 03:49:21 pm »

By good ground I mean a measurement that is within a couple of volts of the mains. If the ground is floating, I have seen we measure a voltage in the Ground wire.

To really know if you have a low impedance ground, you need to provide some momentary fault current and measure it. So, for instance, testers such as the Amprobe INSP-3 and Ideal SureTest Analyzer work by creating a single line cycle "fault" between the line and the EGC "ground" in the receptacle. They then measure how high the ground wire voltage rose to, then calculate an impedance of the fault path. In the US I believe that code calls for less than a 1 ohm impedance of the fault return path back to the G-N-E bonding point. If that same test measures very close to zero ohms, then a bootleg ground in the receptacle/outlet itself is suspected, and some testers such as the SureTest will light up a big F for "False" ground. 
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David Buckley

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Re: Help trouble shoot speaker voltage leak.
« Reply #18 on: November 04, 2015, 06:06:11 am »

From an audio perspective, it doesn't matter if the ground works (in the electrical, safety sense) or not; what is important is that all the ground wires of every device are connected together.  So can the OP confirm that they have a proper distro setup, and that power to the console is run from the distro, alongside the multicore(s)?

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Nitin Sidhu

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Re: Help trouble shoot speaker voltage leak.
« Reply #19 on: November 05, 2015, 02:32:38 pm »

Hello!

As advised, today I metered ground-ground between all receptacles on stage. No voltage. H-N was 231v. H-G was 229, and N-G metered 0 across all. I will assume that this is a single phase distributed through the stage. And we have proper ground.

The speaker is powered up, no audio link.
The FM12 across pins 2-3 would light up my contact voltage tester (one contact neon test light), and cause the speaker to buzz.

The FM when measured with a multimeter (VOM I think for the west) measured 112v across any of the 3 XLR pins on the FM12 and the ground on the power drop. Mike says this could be because of a floating ground. Within the speaker Electronics ? (Note, across all 3 pins)

*Edit : I will ensure our IEC power cables are good tomorrow. Afterthough.

I also did a resistance measurement between the 3 audio pins and the IEC power socket of the speaker. Infinite resistance.

David, when we can, we use our distro, and ensure all is running as should be. However, in many situations, we provide additional tech and gear in venues where installs are available. And do not deploy all our gear. However, we still measure to the best of our education to ensure all is good. This concern is regarding a speaker which I suspect to be leaking high voltage and taking out our console outputs, but only in certain venues. And from our basic measurements, all venues measure well. I really need to get my hands on one of those fancy
tester that Mike suggested... Waiting for someone to take a vacation to India from the US!

Again, thank you all for your time.

Tomorrow I should verify all these measurements again.

Regards,
Sidhu
« Last Edit: November 05, 2015, 03:04:44 pm by Nitin Sidhu »
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Re: Help trouble shoot speaker voltage leak.
« Reply #19 on: November 05, 2015, 02:32:38 pm »


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