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Author Topic: Pulling power for ONE PA, from two different sources?  (Read 18024 times)

Thomas Metz

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Re: Pulling power for ONE PA, from two different sources?
« Reply #10 on: June 21, 2014, 02:43:28 pm »

Another reason not to pull power from different houses in a neighborhood is the potential for VERY high voltages between houses.  A failure in the power company system could put thousands of volts between houses. Get one of the good inverter type of generators and bill them for the rental.

Can you elaborate on that?

I am not making a connection between the houses except they would be feeding equipment that share a copper signal line and a chassis ground.... How in the world could a 220V house service equal "thousands of volts between the houses"...?

Lets say one house somehow loses power... There is no way for the equipment to feed power from one house to another... well, not with out some sort of unrealistic scenario where I had a complete meltdown of a power supply at the exact same moment. And even if somehow, the equipment melt down and fused the hot to earth with out blowing a fuse, and it did connect... the other house would throw a breaker... no problem..

Back to reality, if, there was a ground differential, noise in the system and MY equipment should be the only thing at risk here... unless I am missing something... and I may be...

If you want to help me "please explain why it is a bad thing" don't just give me the cookie cutter response....

I am not opposed to renting a genset, but I am not going to shell out the money for that unless there is a "real danger" of damage of harm.

MY primary concern. House one has a crappy earth ground. One with a large level of resistance between earth and the ground buss. I connect all the equipment, and the ground in house two is fantastic. The crappy ground in house one may find the ground I am using to/from house two... aka, if my connections between the houses equals less resitance on ground, house ONE may try to find ground through my gear and IN house two....

That sounds so confusing... does anyone know what I am talking about?

I am concerned about my cord from house two, hits chassis ground in my rack along with the ground from house one. AND a potential of current dissipation between the houses on the GROUND.

Kind like, when you have a service in a home, and you want to add a sub panel... the way it grounds is very different depending on the relationship between ground and neutral in the main panel. If you start by sharing ground and neutral you can just add another ground rod for your sub panel... it would create two different impedance on the ground/neutral plane...


And Chris, You would think... but "obviously" I have not been able to make that happen.

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Kevin Graf

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Re: Pulling power for ONE PA, from two different sources?
« Reply #11 on: June 21, 2014, 03:22:12 pm »

I must be missing something. These appear to be nearby homes in a quite residential neighborhood. Most likely serviced by the same power company 240V output single phase transformer. Very little difference than powering your system from different circuits in the same building.

Tony Waldron writes about audio systems in large multiple buildings, multiple power source studio complexes.

"Tony Waldron's Audio & EMC ranting and ravings"
http://www.fragrantsword.com/twaudio/

Measurements from one home to the other with a long extension cord using a DMM and a Non Contact Probe could be made this weekend.
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Tom Bourke

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Re: Pulling power for ONE PA, from two different sources?
« Reply #12 on: June 21, 2014, 03:37:07 pm »

Can you elaborate on that?

I am not making a connection between the houses except they would be feeding equipment that share a copper signal line and a chassis ground.... How in the world could a 220V house service equal "thousands of volts between the houses"...?

If they happen to be on the same transformer then the voltage will stay around 220V max.  However the power company distributes power at much higher voltage.  Around 13KV at my last house.  There have also been instances of very high voltage buried cable (tens of KV) leaking stray voltage due to degradation of the insulation.  This is then picked up as a difference in ground potential.  If each house does not share a common electrical ground this can reach high voltages.
http://en.wikipedia.org/wiki/Electric_power_distribution  Also do a search on stray voltage.
« Last Edit: June 21, 2014, 03:44:25 pm by Tom Bourke »
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Ray Aberle

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Re: Pulling power for ONE PA, from two different sources?
« Reply #13 on: June 21, 2014, 03:39:49 pm »

The other advantage of using a small generator is that if a breaker trips in your distro, it's right there and easy to reset. If a breaker trips in one of the houses, you would have to run inside, find their panel, find the right breaker, and reset it =\
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Tim McCulloch

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Re: Pulling power for ONE PA, from two different sources?
« Reply #14 on: June 21, 2014, 03:45:28 pm »

I am not opposed to renting a genset, but I am not going to shell out the money for that unless there is a "real danger" of damage of harm.

Get the pryo guys to rent it and include it in their price.  Really.  The HOA is spending several thou for a shoot and want to get pissy over a genset rental when their members won't/can't up safe, suitable power?  "Intercourse" them.  They're penny wise and liability foolish.

Quote
MY primary concern. House one has a crappy earth ground. One with a large level of resistance between earth and the ground buss. I connect all the equipment, and the ground in house two is fantastic. The crappy ground in house one may find the ground I am using to/from house two... aka, if my connections between the houses equals less resitance on ground, house ONE may try to find ground through my gear and IN house two....

That sounds so confusing... does anyone know what I am talking about?

I am concerned about my cord from house two, hits chassis ground in my rack along with the ground from house one. AND a potential of current dissipation between the houses on the GROUND.

Kind like, when you have a service in a home, and you want to add a sub panel... the way it grounds is very different depending on the relationship between ground and neutral in the main panel. If you start by sharing ground and neutral you can just add another ground rod for your sub panel... it would create two different impedance on the ground/neutral plane...

And Chris, You would think... but "obviously" I have not been able to make that happen.

The bolded text illustrates the issue.  Go back and look through some of Mike Sokol's posts on "reversed polarity, bootleg ground" circuits and what that can mean for signal grounds.  While you're unlikely to encounter one of those, the various differences in power distribution and quality of wiring in general should make you very leery of the possibility of audio pin 1/shield becoming a common ground between houses on different transformers, with your gear in between.  Given that you know there are problems with household circuits/wiring you're expected to use, I'd decline and insist on getting "real power" from another house or generator(s).

I just read Kevin G's reply.  I'll agree that long extension cords, meter and other accessories can make for an educational afternoon.  I'd add that a load should be applied (flood light, toaster, something that draws 1000w) to each circuit and measurements taken to compare with unloaded measurements.  And I'd still want a generator, but maybe that's just me.

Thomas, I understand that we're pretty much dependent on our client's willingness to accept our recommendations, but this is one of the cases where potential safety decisions are being made based on being cheap asses.  Here's what I'd do:  I'd require the HOA to have me listed as an additional named insured on THEIR liability policy as part of my contract, and also require "absolute indemnification for any and all claims arising from any services provided by Thomas Metz."  If they won't do that you can say, "a generator rental is only $300."
« Last Edit: June 21, 2014, 03:48:01 pm by Tim McCulloch »
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Thomas Metz

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Re: Pulling power for ONE PA, from two different sources?
« Reply #15 on: June 21, 2014, 03:54:58 pm »

If they happen to be on the same transformer then the voltage will stay around 220V max.  However the power company distributes power at much higher voltage.  Around 13KV at my last house.  There have also been instances of very high voltage buried cable (tens of KV) leaking stray voltage due to degradation of the insulation.  This is then picked up as a difference in ground potential.  If each house does not share a common electrical ground this can reach high voltages.
http://en.wikipedia.org/wiki/Electric_power_distribution  Also do a search on stray voltage.


THIS... is exactly what I do for a living. LARGE scale production sound/ lighting install. It is not uncommon to have several parts of ONE system fed from different panels and or switch gear in a single building.

BUT.... (see next response)
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Thomas Metz

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Re: Pulling power for ONE PA, from two different sources?
« Reply #16 on: June 21, 2014, 03:57:29 pm »


The bolded text illustrates the issue.  Go back and look through some of Mike Sokol's posts on "reversed polarity, bootleg ground" circuits and what that can mean for signal grounds.  While you're unlikely to encounter one of those, the various differences in power distribution and quality of wiring in general should make you very leery of the possibility of audio pin 1/shield becoming a common ground between houses on different transformers, with your gear in between.  Given that you know there are problems with household circuits/wiring you're expected to use, I'd decline and insist on getting "real power" from another house or generator(s).



THIS... is exactly what worries me and that's why I wrote it...  Thank you for adding some detail!
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Thomas Metz

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Re: Pulling power for ONE PA, from two different sources?
« Reply #17 on: June 21, 2014, 03:59:35 pm »

However the power company distributes power at much higher voltage.  Around 13KV at my last house.  There have also been instances of very high voltage buried cable (tens of KV) leaking stray voltage due to degradation of the insulation.  This is then picked up as a difference in ground potential.  If each house does not share a common electrical ground this can reach high voltages.
http://en.wikipedia.org/wiki/Electric_power_distribution  Also do a search on stray voltage.

This I understand. Thank you.
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Thomas Metz

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Re: Pulling power for ONE PA, from two different sources?
« Reply #18 on: June 21, 2014, 04:07:37 pm »

Ok...

I was worried about it because i do understand that there is the potential for problems. With more insight added I feel that my concerns are warranted.

LOL, the professional pyro... he ALSO live in the neighborhood. lol, they are not getting paid either.... lol.

They project what "donations" will come in to pay for the fireworks and this year they ended up about $1500 short on funds.

Everything else... (labor, sound, food, etc...) is all free volunteer work. Cops and Fire department show up as part of the permit acquisition process.


Looks like I am renting a Genset...

Thanks guys...(or gals)



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Jonathan Johnson

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Re: Pulling power for ONE PA, from two different sources?
« Reply #19 on: June 21, 2014, 04:12:34 pm »

I'm with the others; I don't think this is a good idea. But if you're absolutely determined to go ahead with the plan, I would recommend that all signal lines between the equipment on different circuits be connected via isolation transformers with ground lift.

The potential for ground voltage differential between the systems is high; you don't want your signal line shields to be the balancing factor. To do so not only could introduce hum, but if a significant enough voltage is present, it could damage things and present a shock hazard.

And a warning: ensure that the equipment on different circuits is at least 10 feet physically separated. This will prevent you or anyone else from touching the chassis on two pieces of equipment that are at different ground voltage potentials.

You could also create a grounding grid that bonds the grounds of each house AND the chassis of each distro with a ground rod driven at the equipment location, but the cost of doing that would be more than the cost of renting a generator (which, by the way, should be bonded to a driven ground rod; look here for a discussion).
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Re: Pulling power for ONE PA, from two different sources?
« Reply #19 on: June 21, 2014, 04:12:34 pm »


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