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#42559 09/22/04 09:58 PM
Joined: Apr 2002
Posts: 914
What causes some fluorescent fixtures to not work until they are tapped/touched. I get this question from time to time and never know what to say. On 1 fixture, I replaced the the ballast and the bulbs - twice. The bulbs were making good contact, but most of the time the fixture wouldn't fully come on unless it was touched, why?

#42560 09/22/04 10:22 PM
Joined: Mar 2004
Posts: 947
twh Offline
I had that problem on an 8 foot fixture and solved it by reversing the sockets on one end. That doesn't make a lot of sense, so it was probably a bad wire connection on a socket.

#42561 09/22/04 10:22 PM
Joined: Dec 2003
Posts: 886
Some will say that it is because there is a problem with the equipment ground to the fixture. I don't subscribe to that.

I'll bet this is a 2 "U" tube fixture.

The first thing to do is to make sure that the proper lamps are being used. Check them against the list on the ballast label. While you are there make sure everything is wired correctly and the sockets are in good shape.

I had this problem awhile back. No way could I get the fixtures to work. Some wouldn't light, some would do what yours does. I installed new ballasts, new tubes, checked the sockets and yes, I checked the grounds.

Out of frustration and just because it's easier to work, I removed a ballast wired to the sockets from one of the fixtures that wouldn't light and brought it all back to the shop. I placed them on a metal cart and stuck a couple of new lamps from our stock in the sockets. Wired a 2 wire line cord to the ballast and guess what- the damn thing lit just fine! (Goes to show also that a ground is not necessary for the fixture to light.)

Long story short, the problem was the lamps. Sure, they were the proper ones, Phillips, brand new right out of the box that the customer supplied. Ours were GE- also brand new right out of the box.

I replaced all the customer's lamps with GE's and they have been working ever since.

Go figure!


#42562 09/22/04 10:28 PM
Joined: Dec 2003
Posts: 524
... Had the same problem,..and yes, it was a "U"-tube... when I lowered the lens down,and just lightly touched the bulb, came on,..shut it down,and tried to turn it back on,..nothing,..put my fingertips to the bulb,and VOILA,let there be light,...very strange..could it be a stray static electric discharge phenomenonmenem??

.."if it ain't fixed,don't break a Licensed Electrician"
#42563 09/22/04 11:29 PM
Joined: Jul 2004
Posts: 129
From my experience if allelse is in order the problem is grounding.To confirm if gounding is the problem temporarely place a jumper between the neutral and the fixture case.If the fixture becomes more reliable then you know grounding or lack of is your problen. Fluorscent bulbs need to be within 1/2"of a grounded surface to establish operation once they are lit they no longer need the ground.With that being said I have seen identical fixtures and ballasts some would work fine without grounding some had to be grunded. I replaced a ballast in my shop I thought the ground was OK the fixture was fed with BX the fixture worked fine it would burn for weeks on end sometimes when t turned it off the fuse would blow.After about 6 months of this I ran a seperate ground the fixture works fine now.Thank goodness that this happened in my shop and not on a customers premace.

#42564 09/23/04 12:30 AM
Joined: Dec 2003
Posts: 886
could it be a stray static electric discharge phenomenonmenem??

More like the capacitance of your hand next to the lamp. Why that is different than the metal reflector I don't know.

I think all these problems are due to the energy saving design of both the ballasts and lamps we have nowadays, possibly the low mercury content also. Seems to have started when these became required. Looks like the starting on these things is very marginal. Years ago when nobody cared how much a fixture consumed or the mercury content they seemed to start much more reliably.

When instructions say that the lamps must be within 1/2" of the grounded reflector they are saying that the reflector must be connected to the ballast case not an equipment ground. Many people have this misconception. Of course the NEC requires an equipment ground, but it is not required for the fixture to light. Plenty of shop light fixtures out there with 2 wire cords.

Anybody with finicky fixtures should consider what I said above. Nobody thinks of trying another manufacturers lamps but that may be what the problem is.


#42565 09/23/04 07:12 AM
Joined: Apr 2004
Posts: 55
I have had similar problems on both 4' and 8' tubes. We have recently been forced into using the new "environmentaly safe" tubes. We have used the Phillips and Sylvania versions, and I must say the lifespan of these tubes is abysmal.

We are already replacing the "green" tubes, and we aren't even close to phasing out the old types.

I have also noticed that they are often quite slow to light off. Once they warm up they do pretty well, but that first time is often slow.

Another aspect that causes most fluorescent lamps to be slow to start is temperature. We have a few locations that are unheated, and we have taken to leaving the lights on during the winter months. I had one fixture that took over 2hours to heat up enough to light. I had actually gone for a ladder to tear into it. It lit off about the time I set the ladder up.

#42566 09/23/04 05:24 PM
Joined: Aug 2004
Posts: 186
I dont understand the whole possibilty of it being a ground problem only for the sake that 90% of the time i do tap a bulb to get it to fire it is with one hand and im standing on a fiberglass ladder. Where would the ground be? I dont have a clue what cause's it but i dont feel its a ground issue. I think it has something to do with moving the gas within the tube or a bad tumbstone.

#42567 09/23/04 06:53 PM
Joined: Nov 2001
Posts: 273
i had the same problem with the fixtures at my parents house,touch'em & they would come on. but turn then off, & that was it. so i bought 2 new ballasts, same problem. so i called the ballast manufacturer. they had no answers either.some one said that if the bulbs didn't start together they would not start at all, they jut glowed on the ends of one. so as a final idea i bought 2 brand new bulbs & now they come on every time.this house was built in 1965 so there are no i would say it is not a grounding issue, just maybe some bad ballasts or bulbs. when i wired my shop lites temporairly i used a 2 wire cable & they come on just fine.of course i put up permanent plugs to plug them into.

#42568 09/23/04 07:33 PM
Joined: Dec 2003
Posts: 886
I think this is a poor design issue on both the ballast and lamp manufacturers part. They are so marginal that anything slightly off due to manufacture or aging and they won't light. This is born out by my problem with one brand of lamps working and another wouldn't. I also remember one time when I was replacing fixtures with energy saving ones that used T8 lamps. I had to go through cases of new lamps to find ones that would light reliably in the fixtures.

We bang our heads against the wall trying to get these fixtures to work when all along they really weren't designed to work in the first place.


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