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Author Topic: Low Voltage Concern  (Read 1139 times)

Mark Hannah

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Re: Low Voltage Concern
« Reply #10 on: June 05, 2018, 08:00:12 am »

My guess is that this is an older venue.  460 used to be common-used to even see motors rated at 440 VAC (not in my day-but in motors made back when stuff was made to last decades not years-so I've seen a few-a lot of old prints show nominal 440 or 460 supplies).  The POCO has no incentive to swap out the transformer-just an added expense for something that is already working. That's why I think the voltage issue is a mismatch with a 480-208/120 transformer being fed with 460 nominal.

There is not enough info to tell where the voltage drop is coming from.  A loaded/unloaded measurement on both the incoming service and the 120 v supply would be needed to diagnose that.

It is not an older venue.  The stage is part of a residential/commercial development near a large convention center (opened 2008).  I would share the location but I do not know if the site would be sensitive to such information.  Particularly if I ultimately find it easier to share the whole thread with them rather than compile the advice all of you have shared.

I believe the "local" panel has a higher load on it than it should.  The panel is not labeled.  I am 98.6% certain that the large, outdoor video wall, directly above and behind the stage, is off the panel.

I have no site plan so I cannot provide any details on how far the transformer is from the panel.

Between the 2015 & 2016 summer seasons, I worked with the property management to get mini-cams installed which has made our life much easier.  This allowed us to not climb down into a hot, damp service hole where the breaker panel is.  The site is next to a river, the "hole" is below grade and thus has a sump pump. 

Unfortunately, the email chain is archived in Outlook PST files.  It is on my to-do list to dust of the files and see if there might be additional & helpful information.

Other that getting a queasy feeling as voltage drops are you experiencing any failures or other issues?  I get shit from some touring personnel at one of our venues, particuarly in the summer when the grid is powering a whole bunch of air conditioning and the voltage drops.  They seem to think there is something we can do to make the PoCo flog the little rodents that turn the generators and raise the voltage but the reality is that on site, day of show, we can't do anything.


No failures or damage experienced so far.  There could be accumulative/long term damage that I would never be able to connect to working at this venue.
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Mike Sokol

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Re: Low Voltage Concern
« Reply #11 on: June 05, 2018, 08:05:25 am »

This is illuminating (no pun intended) as I'd never heard of nominal 460v service from a utility company. 
I'm with Swaffer - either there is undersized service wiring, the transformer isn't tapped in the right spot to deliver nominal 120/208v or 120/240v to the secondary, or both.

...a boost transformer, as suggested by TJ, is probably your best option.

I tend to agree with this explanation. I've installed Buck and Boost transformers many times in both my industrial jobs as well as my worship venue jobs. We used them in warehouses to drop 277 volts down to 240 volts for lighting (in buck mode), or increase 208 volts up to 240 volts (in boost mode). Exact same transformer, but to change from buck to boost you just reverse the output winding to be either in or out of phase with the primary feed. Since they're not carrying the full load, just the full current times the small voltage difference they're adding or subtracting from the main feed, they're much smaller and cheaper than what you need for a full isolation transformer carrying the full KVA of the entire load.

Don't expect residential electricians to know what they are. But any good industrial electrician should have experience with Buck and Boost Transformers and know how to install them.
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Craig Hauber

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Re: Low Voltage Concern
« Reply #12 on: July 02, 2018, 12:55:33 pm »

This is illuminating (no pun intended) as I'd never heard of nominal 460v service from a utility company.  Yes on 480 but not 460.

I've never heard of nominal "110" or "220" either, but that's what everyone asks for around here in farmville  :)
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Craig Hauber
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Mike Sokol

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Re: Low Voltage Concern
« Reply #13 on: July 02, 2018, 06:35:16 pm »

I've never heard of nominal "110" or "220" either, but that's what everyone asks for around here in farmville  :)

IIRC Edison's original spec called for 100 volts of DC which drew 1 ampere of current for a 100 watt light bulb. He soon raised it to 110 volts to compensate for the voltage drop in wiring. Later it was raised again to 115 volts (in the 60's, I think), then finally 120 volts in modern times, give or take 5% on a branch circuit under load. That's plus or minus 6 volts, so you could measure as low as 114 volts and as high as 126 volts on a branch circuit under load and still be within NEC specs.
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Guy Holt

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Re: Low Voltage Concern
« Reply #14 on: July 05, 2018, 10:58:10 am »

It is not an older venue.  The stage is part of a residential/commercial development near a large convention center (opened 2008).... I believe the "local" panel has a higher load on it than it should.  The panel is not labeled.  I am 98.6% certain that the large, outdoor video wall, directly above and behind the stage, is off the panel.

What else has changed since 2008, when the distro system was designed, has been the pervasive use of LEDs in stage lighting. I have found that a lot of LED AC power supplies are not power factor corrected (pfc). With power factors as low as .45, LEDs can draw considerable harmonic currents. The harmonic currents will cause additional voltage drop due to skin and proximity effects which cause the higher frequency harmonic currents to travel through only a narrow band near the surface of the conductor. Where more current is traveling through less copper, resistance increases and voltage drops. Recent studies in the EU have found that house distribution should be de-rated by 50% or more when powering large numbers of non-pfc LEDs.


(The Chauvet Slim Par Pro RGBA has a pf of .61 and Total Harmonic Distortion of 81%)

The manufacturers of LED Light fixtures generally do not give power factor specifications for their products. Over half of the fixtures that I tested at random (from the inventories of Boston area rental and lighting sales companies) were not pfc. With power factors ranging from .45 to .63, these fixtures generated considerable harmonic distortion (THD ranged from 75-85%.)

For those interested, I am writing a series on power quality in the age of LEDs for Protocol magazine.  If you are not familiar with Protocol, it is the quarterly publication of ESTA Ė an international organization working to raise standards, improve skills and strengthen the events, entertainment and installation industries. If you canít find the print edition of the magazine, there are links on our webpage at www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html.

Guy Holt, Gaffer
ScreenLight & Grip
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