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Author Topic: Odd voltage readings  (Read 3072 times)

Stephen Swaffer

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Odd voltage readings
« on: May 01, 2017, 12:24:44 pm »

Quote from Church Sound:

"Hey Eric
I could give you a few,
This is one we just finished a few weeks ago and is power related. We did a full AVL in North Georgia.

They had three phase power coming into the building and split out to three old dimmer panels that had been converted into straight power panels. The church didn't tell us or the electrician's that a DIY relay system had been installed in the 80s, that was wired into another panel in another closet, all of the outputs from each of these breakers in the old dimmer went to this relay system.

After the electrician got us outlets at all of our points we started powering audio gear and hanging lighting fixtures, changing the load on this 1980s diy system caused the relays to fail and to close whenever load was added to them and in turn sending 360v to each outlet, the only time it would show 360v is when there was load on the circuit (multi-meter read 120 until load was added)and the electrician only provided single outlets so it took some time to figure out.
The pastor later informed us that he knew about the relay issue and they had similar issues in other places and didn't tell us because he knew that it wasn't up to code and the whole campus was done that way by his brother 20+ years ago.
8 lighting fixtures, 1 dmx splitters, 1 Jands CL controller, 2 power amps and a Protea fried."

I have to ask-how did failed relays place 260 volts on the receptacles?
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Steve Swaffer

Benjamin Gingerich

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Re: Odd voltage readings
« Reply #1 on: May 02, 2017, 12:46:14 am »

Quote from Church Sound:

"Hey Eric
I could give you a few,
This is one we just finished a few weeks ago and is power related. We did a full AVL in North Georgia.

They had three phase power coming into the building and split out to three old dimmer panels that had been converted into straight power panels. The church didn't tell us or the electrician's that a DIY relay system had been installed in the 80s, that was wired into another panel in another closet, all of the outputs from each of these breakers in the old dimmer went to this relay system.

After the electrician got us outlets at all of our points we started powering audio gear and hanging lighting fixtures, changing the load on this 1980s diy system caused the relays to fail and to close whenever load was added to them and in turn sending 360v to each outlet, the only time it would show 360v is when there was load on the circuit (multi-meter read 120 until load was added)and the electrician only provided single outlets so it took some time to figure out.
The pastor later informed us that he knew about the relay issue and they had similar issues in other places and didn't tell us because he knew that it wasn't up to code and the whole campus was done that way by his brother 20+ years ago.
8 lighting fixtures, 1 dmx splitters, 1 Jands CL controller, 2 power amps and a Protea fried."

I have to ask-how did failed relays place 260 volts on the receptacles?

Hey Stephen
This is what we believed happened. We did not take back to shop and confirm on a bench though.
There were very old 6way relays bolted to plywood in a homemade panel.

Each relay had 3 hot wires coming in from the converted dimmer panel and 3 wires going out to what used to be their old house lights and a 6pair multicore wire that went to two different control locations 
Our thought is that as we started changing the load on these relays they didn't know what to do and closed all three incoming circuts to a single output with the most load. 
I could be wrong. But when the electricans removed the relay system from the chain, everything worked as expected.
They also ended up replacing the old panels, but not for another 2 weeks.
 
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Benjamin Gingerich
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TJ (Tom) Cornish

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Re: Odd voltage readings
« Reply #2 on: May 02, 2017, 06:54:43 am »

Hey Stephen
This is what we believed happened. We did not take back to shop and confirm on a bench though.
There were very old 6way relays bolted to plywood in a homemade panel.

Each relay had 3 hot wires coming in from the converted dimmer panel and 3 wires going out to what used to be their old house lights and a 6pair multicore wire that went to two different control locations 
Our thought is that as we started changing the load on these relays they didn't know what to do and closed all three incoming circuts to a single output with the most load. 
I could be wrong. But when the electricans removed the relay system from the chain, everything worked as expected.
They also ended up replacing the old panels, but not for another 2 weeks.
Is that a peak hold reading, or was that a sustained measurement?  I'm with Steve - 360v isn't a number relays should be able to cause. 120, 208, 240, 277, 480 yes; 360 no. Were the dimmers some kind of autotransformers that somehow got back-fed?  Some weird HID lamp ballast that got back-fed?
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Benjamin Gingerich

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Re: Odd voltage readings
« Reply #3 on: May 02, 2017, 10:34:20 pm »

Is that a peak hold reading, or was that a sustained measurement?  I'm with Steve - 360v isn't a number relays should be able to cause. 120, 208, 240, 277, 480 yes; 360 no. Were the dimmers some kind of autotransformers that somehow got back-fed?  Some weird HID lamp ballast that got back-fed?
Sustained reading, fluctuations of just a few volts. One of the electricans made the same point though.
His thought was there had to be another issue somewhere.
I may be wrong on the contacts causing the issue, however, once the contacts were gone all voltage issue went away, weeks before they changed the dimmers to normal panels
Here is the only pic I could find of the old dimmer panels.
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Benjamin Gingerich
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Benjamin Gingerich

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Re: Odd voltage readings
« Reply #4 on: May 02, 2017, 10:42:51 pm »

Pic
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Benjamin Gingerich
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Tom Bourke

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Re: Odd voltage readings
« Reply #5 on: May 03, 2017, 01:35:28 am »

Is that a peak hold reading, or was that a sustained measurement?  I'm with Steve - 360v isn't a number relays should be able to cause. 120, 208, 240, 277, 480 yes; 360 no. Were the dimmers some kind of autotransformers that somehow got back-fed?  Some weird HID lamp ballast that got back-fed?
One thought is 120 + 240= 360  Also 480 -120 = 360.  If multiple transformers are in play and a neutral and a hot are crossed without proper bonding then you could have one transformer acting as a buck or boost transformer.  Depending on how the wires are crossed and how the relays get activated it may take a load on one part of the system to energize another.
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Daniel Levi

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Re: Odd voltage readings
« Reply #6 on: May 03, 2017, 02:29:47 am »

Like others I'm thinking (with my little knowledge) that 240v + 120v 180 out of phase on the other side (either L1+L2 or L1+N RPBG) would give 360 P-P or the same but with 120v + 480v 0 out of phase would produce 360 P-P. Or could the supply being for some reason 90 out of phase produce the extra 120v needed.
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Mike Sokol

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Re: Odd voltage readings
« Reply #7 on: May 03, 2017, 05:34:12 am »

Something is very strange about this. Unless there's additional transformers involved, there's just no way to get 360 volts out of that panel. Was there some sort of step-up or step-down transformers in the relay system? Even if there was power somehow input from a second panel, there would need to be a transformer feeding it with a floated and stacked neutral on top of one of the first panel's hot legs,

Now I have seen meters go a bit crazy at time with a triac dimmer in the circuit. That's not the true voltage, just the meter reading the peak instead of translating it to RMS. But I'll have to think on this more. 
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John Roberts {JR}

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Re: Odd voltage readings
« Reply #8 on: May 03, 2017, 09:51:42 am »

Something is very strange about this. Unless there's additional transformers involved, there's just no way to get 360 volts out of that panel. Was there some sort of step-up or step-down transformers in the relay system? Even if there was power somehow input from a second panel, there would need to be a transformer feeding it with a floated and stacked neutral on top of one of the first panel's hot legs,

Now I have seen meters go a bit crazy at time with a triac dimmer in the circuit. That's not the true voltage, just the meter reading the peak instead of translating it to RMS. But I'll have to think on this more.
Just a WAG but low battery voltage in the meter could cause a low reference voltage that could overstate the reading...  or something else completely different.

JR
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Stephen Swaffer

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Re: Odd voltage readings
« Reply #9 on: May 03, 2017, 12:42:49 pm »

I assume they were using the same meter-so 120 VAC no load to 360 VAC loaded?

Normally a phantom voltage or a goofy triac reading should smooth out and be more accurate under load.

I doubt there was any 480 in the building.

Perhaps if the dimmers had isolation transformers and somehow got cross connected?

I'm also curious what kind of lighting was in there before that was easier on the relays and/or survived this kind of a wiring scheme?  Obviously, whatever modifcations the electricain's made in adding outlets was based on some incorrect assumptions.  (perhaps assuming that white was neutral?).  If adding a load caused the relays to close, the relay coils must have been in series with the load-if they were chattering instead of just closing this voltage might have been created?

People fuss about requiring electrician's for jobs-but this is one reason why my inspector's don't want non-electricians changing out the type of light fixture-of course, electrician's make mistakes, too!  At least it was only equipment and not people that was damaged.
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Steve Swaffer

ProSoundWeb Community

Re: Odd voltage readings
« Reply #9 on: May 03, 2017, 12:42:49 pm »


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