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Electrical Question on Fluorescent Lamps (not antique)

Reed Engine

Subscriber
Last Subscription Date
07/10/2019
I have a florescent tube fixture in my shop. It has two 8 ft tubes and they needed replacing so I bought new and when installed they wouldn't light up properly so I assumed it was the ballast and bought a new one. The old had 4 wires, black, white, red and blue. The new has 5 wires, black, white, red and two blue. I was told to just cap off one of the blues and did.

Here's my problem, when I turn the light on it comes on bright but immediately goes dim and flickers. I did try other tubes from another fixture that work, they do the same. What's wrong?
 

MarkBillesbach

Registered
Last Subscription Date
07/01/2018
Reed, you have to wire it differently than the old ballast. On the new ballast, the 2 blue wires will go to one end of the fixture and each will land on a single tube socket. The red will go to the other end of the fixture and will attach to both of the other socket ends (you will need a jumper wire between the 2 sockets on that end). The black is the hot wire and the white is the neutral wire and will attach to the incoming power supply wires for the fixture. Hope this makes sense, Mark

---------- Post added at 01:31:09 PM ---------- Previous post was at 01:26:24 PM ----------

Also make sure your using the right bulbs for the ballast. If the new ballast is a T8 ballast, you must use T8 bulbs, don't mix T8 with T12. Also make sure the ballast isn't a HO ballast. Mark
 

len k

Subscriber
Last Subscription Date
12/12/2018
Got to wire it as new ballast says.

On a smaller length light ( ~ 3ft) when I replaced the old balast with a new store bought one I had to ground the metal fixture to get the bulb to initially fire off and light. But your problem sounds different.

I cheated , house wiring didn't have a green safty ground , so I added a cap from the neutral to the fixture metal instead. I calculated the cap to limit current to ~ 2 mA at 60 hz so GFI would not trip ( at 5 mA), salvaged cap from input filter stage of a VCR power supply. Not sure if the cap's voltage rating is right , but it worked.
 

Frank DeWitt

Subscriber
Last Subscription Date
12/17/2019
Another approach for next time. I had a collection of old and very old 4 ft fluorescent fixtures. As ballasts failed and bulbs got more expensive I bought 10 4 ft LED bulbs and went through and rewired them all. 120 vac 1 wire to each end, no ballest. I like. It.
 

Radiomike

Registered
There should be a schematic on the new ballast, follow this. What rating are your tubes?

8 foot tubes are usually T12 (1.5''); as long as the ballast is rated for T12 and 8 foot tubes all should be well. LED replacements are out there, some work with the old ballast some do not. It is just price that will decide. Two 4 foot LEDs could and should work nice. You will even have a choice of colour from 2700°K to 6500°K, as you have with fluorescent tubes.

https://electrical-systems-lighting.knoji.com/how-to-replace-fluorescent-light-ballast/

Mike
 

len k

Subscriber
Last Subscription Date
12/12/2018
If you use an old ballast look it over and see if it has a class P rating. Some very old ballast don't. The P rating means protected, it has a thermal protector inside it. We have had old ballasts without that rating that overheat, leak out the tar filler and catch fire if you leave it on for good portion of the day. So throw out the ballast if it doesn't have P rating.

Because of this overheating issue I like to mount fixtures with an air gap to wood, like in an unfinished garage or cellar. I mount to a 2x4 spacer , located far from the ballast.
 
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slip knot

Subscriber
Last Subscription Date
12/27/2019
follow the schematic on the ballast. Also be aware that the common ballast sold in the box stores are not residential rated. not a big issue unless you like to listen to radio while the lights are on. They create lots of interference on FM radio.
 

Railroads

Registered
Got to wire it as new ballast says.

On a smaller length light ( ~ 3ft) when I replaced the old balast with a new store bought one I had to ground the metal fixture to get the bulb to initially fire off and light. But your problem sounds different.

I cheated , house wiring didn't have a green safty ground , so I added a cap from the neutral to the fixture metal instead. I calculated the cap to limit current to ~ 2 mA at 60 hz so GFI would not trip ( at 5 mA), salvaged cap from input filter stage of a VCR power supply. Not sure if the cap's voltage rating is right , but it worked.
Len, The SMPS VCR supplies have 200V caps in the ones I've worked on. But since these are electrolytics I am a bit surprised they worked out on AC.

I would have thought you would need a AC motor run or a old 0.76uf from one of those throwaway specials from Wally World. Microwave caps are similar to a AC motor cap in construction.

Robert
 

len k

Subscriber
Last Subscription Date
12/12/2018
I used a cap before the electrolytic cap. The caps I used were the small rectangular EMI type filter caps that go right across the AC power line before the power gets rectified and dumped in the Main 1-st stage DC power storage cap of the VCR switching power supply ~ 180VDC. Since the peak of the 120 line is ~ 180 V, I'ld guess the EMI caps were rated 300 V. But I've seen DC power storage caps of a VCR that was only rated for ~ 180 VDC.

I think the balast just gives one quick spike to start the arc in the light, so likely don't need a run cap. In fact before I added the cap when it wouldn't light off initially I just momentarily touched a ground wire from the sink to the fixture and bulb lit. Bulb stayed lit after I Removed that ground wire from fixture, untill I shut it off . Then needed to repeat the process.
 

Radiomike

Registered
There is a class of capacitors for safety applications, class X and Y. These have the relevant safety certification, VDE - UL and CSA. Class X is for use between phase and neutral, class Y between phase (or neutral) and ground. Class Y2 is probably the most common for consumer electronics between phase and ground.. These are designed to fail open circuit.

http://www.justradios.com/safetytips.html

Mike
 

len k

Subscriber
Last Subscription Date
12/12/2018
Yes I think the ones I used were the X and Y type. They were located after the main 120V fuse and either before or after the EMI choke coils, and definitely before the rectifier section.
 

Railroads

Registered
Ok Len, That makes sense then. I've used the orange tear drop type across AC mains with no issues. The yellow square type caps from PC PSU's are my next go to option.

Interesting they won't start without the earth connection present. Did you try connecting the earth and neutral lines together?

Robert
 

len k

Subscriber
Last Subscription Date
12/12/2018
Interesting they won't start without the earth connection present. Think balast even says fixture MUST be grounded.

Did you try connecting the earth and neutral lines together? No safty ground (earth) wire going to fixture.

My problem is house is ~ 58 years old, no green safty ground wire in house wiring. Only a hot and a neutral. That's why I had to add a cap to the neutral to simulate ground. Likely the balast zaps bulb with a spike and capacive coupling to fixture ionizes gas in bulb. Likely same idea as a Xenon strobe bulb's 3-rd lead.

I suppose I could have tied the fixture directly to the neutral , but I didn't like that idea since the first fixture I did this to was on the bathroom ceiling. It would have worked but if the neutral back to the breaker panel opened up then the fixture would be hot. Besides doing that is against (modern) code, they did stuff like that up till ~ 70's (ovens stoves, driers).
 
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Reed Engine

Subscriber
Last Subscription Date
07/10/2019
I ask the city electrician about this and he just happened to have an old ballast that was exactly like the one removed. he gave it to me I wired it in and the lights are on. The new one is setting on the shelf.
 

Buzzzz

Registered
If its a rapid start ballast (lamps will have two pins on each end) then there should be grounded metal close to the lamps to ensure reliable starting.

It sounds like the OP has F96T12's commonly referred to as "slimlines" they have one pin on each end. They are not rapid start.

The new ballast he got was likely an electronic ballast rather than a magnetic like the original. They need to be wired differently but it's easy to figure out just by looking at the diagram provided on the ballast label.

On a side not if your using energy saving lamps, get rid of them. They can really shorten the life of ballasts. The full wattage lamps can be a little harder to find but it's worth it. Full wattage F96's are 75 watt, 60 watt is energy saving lamps. Full wattage F40's are 40 watt, 34 watt energy saving.
 
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