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Flickering Low Voltage lighting.

28397 Views 14 Replies 5 Participants Last post by  frank
I am working on a project installing a ton of lighting in a commercial warehouse being converted to apartments.

I have a problem with all of my AC low voltage lighting. It is flickering very noticeably. All the line voltage stuff seems fine. The problem is on at least two different circuits and moving the circuit to another phase has no effect. Shutting down the only large piece of equip. (cooling tower) has no effect. I did that because there was a time period one night when the flickering stopped.

I am thinking I have a bad neutral or ground connection somewhere in the building. I plan to do a visual inspection of all of the service equipment to look for visual signs of heating or bad connections.

Any other ideas of what it could be? Outside of a visual inspection don't feel comfortable troubleshootong this problem since it is after-hours work and I am not covered by insurance if something happens to me.

In the meantime I have instructed the owner not to use any of the low-voltage lighting for fear of damaging the transformers.

Thanks for your input!
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While a properly grounded/bonded system is important, it is HIGHLY unlikely a ground could be causing this issue. As for a loose neutral, if you had a loose neutral and the load is balanced perfectly across the 3 phases there would be little or no problem, if the load has excessive imbalance you would be losing equipment FRYING the equipment due to over voltage.

What I would do.
If the flicker is happening all the time.

1. Use a multimeter and amp clamp (3 phase high speed recorder would be best) on min max and watch each phase voltage and current at the main service. Determine if the voltage drop is evident with a current increase of the site. As noted below a dip of 3. VAC can result in noticeable flicker.
2. Verify all connections from main service to load distribution panels. Once again expensive equipment would help facilitate this (IR Camera).
3. If you have voltage dips and no current increase then the issue is upstream of the service on the utility distribution. (assuming this is not a connection issue in your establishment).
4. Have you contacted the utility?

THIS is from a post I had on another forum.
This house had an unusual number of incandescent light fixtures 150+, and 7 HVAC units. This house had a 200 amp service that was upgraded to 600 amp, appears the utility left the 200 amp triplex in use, about 150" changed to 250 AL underground 150, plus what appears to be a 30 KVA pole mounted transformer (300 feet away).

Flicker is not just load, conductor length or transformer sizing dependent, it is also end user sensitive. I have flicker but never really notice it, unless the wife says something. I have been to customers houses where it PLAIN WAS DRIVING the homeowner crazy and max VD recorded was 3 VAC. Others are just worried they have connection issues (a legitimate concern).

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Great post Brian.

My advice to Thunderpaste would be - do not worry about damaging the transformers. You just will not affect them in any way. I suspect some voltage reduction at the transformer or downstream to the light fittings . Is the low voltage lighting 12 volts? It is a critical operating voltage. If the lighting is fed via 1 single transformer per leg - did you account for the heavy current demands of the supply cable. ie 4 amps per 50 watts. Both these issues will produce the problems you describe. And lastly - 'cos it has happened to me. Does the flicker seem more prevalent in the afternoon and early evening. Also mid morning. If so check for utility over demand at critical periods. Just one final note. Do the fluorescent tubes in the property 'swirl.
Good indication of low voltage.

These aren't electronic power supplies by chance, are they, rather than a regular transformer? I've had some issues with some of the Chinese electronic low voltage power supplies.
The flickering is BAD. Anybody would definitely notice it.

The transformers are AC and they state 11.5 volt output. I measured 10.8 though. A little low but would this cause the flickering? Could it be they are on electronic dimmers? They are Lutron dimmers and must have a load in order to work properly and fully energize the circuit although there is always line voltage even when turned off, just not much current.

I measured 123 volts from phase to neutral on two legs of a 120/208 panel and 124 on the other leg. Voltage between phases was 214.

I haven't gone upstream from the panel the circuits are on yet.

Thanks for the input. Next time I am there I will report back on my findings.
Could it be they are on electronic dimmers? They are Lutron dimmers and must have a load in order to work properly and fully energize the circuit although there is always line voltage even when turned off, just not much current.
OMG!!!!! That's your problem. I never thought to ask that. Change out to a regular snap switch and see if your problem disappears. I'd bet you 20 bucks that it does go away.

Are these the magnetic rated dimmers that you're using, by the way? If you do not use a magnetic rated dimmer on the primary of the low voltage transformer, and you only use a regular dimmer, the connected load will absolutely flicker.

From Lutron's site:

Yes. Dimming is done on the primary side and a low voltage dimmer will only work. The important thing to note is that if you are using a magnetic transformer, you must use a magnetic dimmer and if you are using an electronic transformer, you must use an electronic dimmer. If you do not, there may be some humming and flickering of the lights, it will not work at all, and you could damage the dimmer."
Many thanks! I really dislike those dimmers anyway! I should have suspected them first.
Many thanks! I really dislike those dimmers anyway! I should have suspected them first.
Wait for the sticker shock when you (or your boss or your customer) sees the price on the magnetic rated dimmers. They're about 33% more in cost over the identical non-magetic rated dimmer, and there's usually a lead time on them if you need more than just a few.
I should add that I like Lutron dimmers. I think they make a fine product, and they're my only brand of dimmer. You just need to use the right one for the right application is all. Lutron had THE BEST technical support you'll ever have the pleasure to call. They even speak good english.

I don't know if they're doing any better now or not, but I had some trouble a few years back related to my dumb self and magnetic rated dimmers. I was doing a job with Lutron Ariadni dimmers. Some were regular and some were magnetic rated. I opened all the packages in mass, and laid all the dimmers out. After the dimmer was out of the pack, there was no way for me to tell which dimmers were magnetic rated for my low voltage lights and which were regular for my regular lights. I had to call Lutron tech support and they had me ohm something out to tell the difference. That's my only warning to you. I wished they would have just put a sticker on the magnetic rated one's at that time. It would have saved me from screwing myself.
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typical me over copmplicate a simple issue.
typical me over copmplicate a simple issue.
No, on the contrary. Your post was very informational, and I for one appreciate it. Everyone looks at a given problem with a certain bent.
That was definitely a great post.
That was definitely a great post.
I think need to have smoke after that one, it really did have it all :rolleyes:
Marc: One thing I tell people I am a power guy and know little and nothing about lights...also makes it easy to push off side jobs.
Never use electronic dimmers unless I have to. I like the toroidal best. They last forever and are not prone to any of the problems that have been posted above. Great post that will help lots of folks for sure.

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