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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Jamin Lynch on September 05, 2014, 06:27:49 pm

Title: Voltage issue
Post by: Jamin Lynch on September 05, 2014, 06:27:49 pm
I was helping a band at a local club when their Furman power conditioner suddenly shut down. The display showed "OL" overload. I unplugged everything and metered the outlet. 139 volts. Another outlet metered 109 volts. We ended up finding enough outlets that all metered 109 volts and everything went OK.

I went around and metered a few others and found most were 109 volts but 2 were 139. What could be the problem?

Thanks
Title: Re: Voltage issue
Post by: Tim McCulloch on September 05, 2014, 06:50:25 pm
I was helping a band at a local club when their Furman power conditioner suddenly shut down. The display showed "OL" overload. I unplugged everything and metered the outlet. 139 volts. Another outlet metered 109 volts. We ended up finding enough outlets that all metered 109 volts and everything went OK.

I went around and metered a few others and found most were 109 volts but 2 were 139. What could be the problem?

Thanks

Floating neutral.  They need an electrician, pronto.
Title: Re: Voltage issue
Post by: Jamin Lynch on September 05, 2014, 06:57:49 pm
Floating neutral.  They need an electrician, pronto.

OK.

Just for my own information, what specifically would the electrician do to correct a floating neutral?
Title: Re: Voltage issue
Post by: Tim McCulloch on September 05, 2014, 07:03:24 pm
OK.

Just for my own information, what specifically would the electrician do to correct a floating neutral?

That's a trade secret.  If I tell you.....

Seriously, it means that somewhere between the PoCo's transformer and the outlets, the neutral connection is loose, corroded, or otherwise not maintaining it's bond to the grounding electrode network.  In a typical split (single) phase system with a bad neutral, whichever leg has the higher load will have lower voltage.  The voltage can swing back and forth as loads come on line or go off line.

If you found this at multiple outlets my guess is that the problem is in the bar's breaker box, at the meter base, or possibly upstream at the PoCo transformer.  Are there other adjacent businesses and are they reporting problems?  If no probs, I'd say its in the bar's box or meter base.
Title: Re: Voltage issue
Post by: Jamin Lynch on September 05, 2014, 07:12:39 pm
That's a trade secret.  If I tell you.....

Seriously, it means that somewhere between the PoCo's transformer and the outlets, the neutral connection is loose, corroded, or otherwise not maintaining it's bond to the grounding electrode network.  In a typical split (single) phase system with a bad neutral, whichever leg has the higher load will have lower voltage.  The voltage can swing back and forth as loads come on line or go off line.

If you found this at multiple outlets my guess is that the problem is in the bar's breaker box, at the meter base, or possibly upstream at the PoCo transformer.  Are there other adjacent businesses and are they reporting problems?  If no probs, I'd say its in the bar's box or meter base.

Got it.

Sounds like a job for superman
Title: Re: Voltage issue
Post by: Tim McCulloch on September 05, 2014, 07:18:32 pm
Got it.

Sounds like a job for superman

Or a licensed electrician.  Leave the Kryptonite at home, just in case.
Title: Re: Voltage issue
Post by: Jamin Lynch on September 05, 2014, 07:23:23 pm
Or a licensed electrician.  Leave the Kryptonite at home, just in case.

We mentioned the issues we were having that night. We got the typical I don't care owner response. "None of the other bands have a problem."

If we can't get it fixed, would a voltage regulator do any good? Is there potential for equipment damage or injury?
Title: Re: Voltage issue
Post by: Stephen Swaffer on September 05, 2014, 07:47:17 pm
The last floating neutral I dealt with was reading something like 60 volts on one side and 180  on the other and since the ground wasn't done correctly either, the furnace and appliances were showing hot with a NCVD.  As Tim pointed out the voltage can swing and if it is a loose or corroded connection can you guarantee the connection just won't? completely open up?

IMO, if you use it again, only take along gear you consider disposable, but that's just me.
Title: Re: Voltage issue
Post by: frank kayser on September 05, 2014, 07:53:35 pm
Tell 'em to fix it or find someone else.   Hell, call the fire marshall/building inspector.
Just my opinion...
frank
Title: Re: Voltage issue
Post by: Tim McCulloch on September 05, 2014, 08:23:41 pm
We mentioned the issues we were having that night. We got the typical I don't care owner response. "None of the other bands have a problem."

If we can't get it fixed, would a voltage regulator do any good? Is there potential for equipment damage or injury?

The nights the other bands have played, there could have been different loading of the electrical service and less voltage swing.  A lack of other complaints could also mean the other bands knew that mentioning it would get no response.

When his frozen drink machine quits or the ice machine stops making ice, enjoy the schadenfreude.

And yes, Virginia, there is an Electro-Claus.  He's off killing some VooDoo Labs pedal power box right now... or worse to anything without "universal PSU."
Title: Re: Voltage issue
Post by: Ray Aberle on September 05, 2014, 08:42:51 pm
The nights the other bands have played, there could have been different loading of the electrical service and less voltage swing.  A lack of other complaints could also mean the other bands knew that mentioning it would get no response.

Alternatively, the other bands are idiots and didn't have any problem because they didn't even know enough to look........

-Ray
Title: Re: Voltage issue
Post by: frank kayser on September 05, 2014, 09:04:39 pm
Alternatively, the other bands are idiots and didn't have any problem because they didn't even know enough to look........

-Ray
The way I understand a floating neutral problem is sometimes you get lucky, and sometimes you don't. If folks happen to plug in in a  way that keeps both legs +/- 10v, no one is the wiser.  But that can change mid-set when something in the kitchen or an air conditioner kicks in or out. 
frank
Title: Re: Voltage issue
Post by: Mike Sokol on September 05, 2014, 09:30:12 pm
The way I understand a floating neutral problem is sometimes you get lucky, and sometimes you don't. If folks happen to plug in in a  way that keeps both legs +/- 10v, no one is the wiser.  But that can change mid-set when something in the kitchen or an air conditioner kicks in or out. 
frank

You'll always remember your first open neutral.  ;D  That's because you'll be paying for the repairs for a  LONG time. Seriously, I've seen entire back-lines taken out when the voltage climbed to 180 volts.

A slightly different cause can be from an undersized neutral in a club that was previously wired for 3-phase industrial power. Many times the POCO would use a smaller neutral to save copper since 3-phase motors don't produce any neutral currents. But in a club with a lot of single-phase loads such as lighting, I've been able to pull the neutral around by 10 or 20 volts just by changing the lighting load on the other phase. If that's indeed the case, then it requires more than tightening a few loose screws, it will need an upgrade by the POCO. You can get an electrician to check for this neutral problem by opening the main service panel and inspecting the incoming wire gauges to make sure they're all sized the same. Don't do this yourself unless you're authorized by the club owner and licensed to open up the panel. There will be live wires inside that also have arc-flash current capabilities. You need to be really careful with this stuff.
Title: Re: Voltage issue
Post by: Jamin Lynch on September 05, 2014, 09:45:00 pm
You'll always remember your first open neutral.  ;D  That's because you'll be paying for the repairs for a  LONG time. Seriously, I've seen entire back-lines taken out when the voltage climbed to 180 volts.

A slightly different cause can be from an undersized neutral in a club that was previously wired for 3-phase industrial power. Many times the POCO would use a smaller neutral to save copper since 3-phase motors don't produce any neutral currents. But in a club with a lot of single-phase loads such as lighting, I've been able to pull the neutral around by 10 or 20 volts just by changing the lighting load on the other phase. If that's indeed the case, then it requires more than tightening a few loose screws, it will need an upgrade by the POCO. You can get an electrician to check for this neutral problem by opening the main service panel and inspecting the incoming wire gauges to make sure they're all sized the same. Don't do this yourself unless you're authorized by the club owner and licensed to open up the panel. There will be live wires inside that also have arc-flash current capabilities. You need to be really careful with this stuff.

Me no touchy  ;D

This is not a very large place. I believe it was a convenience store previously.
Title: Re: Voltage issue
Post by: Stephen Swaffer on September 05, 2014, 10:36:35 pm
Then Mike's suggestion of an undersize neutral might be very possible.  A high percentage of a convenience store's power is refrigeration and commercial refrigeration is often 3 phase, their single phase loads would be relatively light. If it is a small place, a competent electrician should be able to find the problem (and fix it, if it is just loose/corroded) in an hour or 2 at the most-that would be far less costly than replacing gear.

Perhaps if everything is running on universal power supplies it might be ok-but depending the relative locations of the "problem" and the ground/neutral bond it could be a serious safety issue as well.
Title: Re: Voltage issue
Post by: Tim McCulloch on September 05, 2014, 10:53:58 pm
Me no touchy  ;D

This is not a very large place. I believe it was a convenience store previously.

I'm liking Mikes undersized neutral hypothesis, especially with Steve's comments added in.
Title: Re: Voltage issue
Post by: Tom Bourke on September 06, 2014, 09:57:58 pm
Or a licensed electrician.  Leave the Kryptonite at home, just in case.
Make that a competent licensed electrician. First time I ran into a floating neutral it had burned up a fuse panel.  I had to explain to the kid they sent out how a burned panel could make some lights glow brighter!  It was a four-plex apartment building and the original install had a #14 wire running threw all 4 panels! :o
Title: Re: Voltage issue
Post by: Jonathan Johnson on September 07, 2014, 01:55:48 am
If we can't get it fixed, would a voltage regulator do any good? Is there potential for equipment damage or injury?

There is potential for equipment damage. Too high of voltage could case internal arcing or damage to wiring or circuit traces. That in turn could lead to a hot skin condition on equipment. Personnel could receive an electrical shock. (OK, so this is worst-case scenario.)

If you can't get it fixed, you could argue breach of contract -- if your contract specifies electrical requirements. A rider might include something to the effect of "band may require electrical systems to be tested and inspected prior to connection by a licensed electrician at the venue's expense. Any deficiencies shall be corrected at venue's expense prior to connection."
Title: Re: Voltage issue
Post by: Jeff Bankston on September 07, 2014, 05:11:35 am
Tell 'em to fix it or find someone else.   Hell, call the fire marshall/building inspector.
Just my opinion...
frank
exactly
Title: Re: Voltage issue
Post by: Mike Sokol on September 07, 2014, 10:55:05 am
I'm liking Mikes undersized neutral hypothesis, especially with Steve's comments added in.

Any time you see a 3-phase industrial service panel that's been re-purposed for single-phase lighting and amplifier loads, that's the time to be suspicious that the neutral might be sized too small. The POCOs used to do this all the time and it's caught me unawares a few times.