The Prudential Ltg. P-43 Fixture
Towards the end of a recent, small remodel, we received an item on our punch list concerning a certain fixture: ”Dimmer and ballast may not be compatible.” Upon further inspection, we observed that when the fixture in question was dimmed below 50%, one of the two lamps began to abruptly shift between a dim and a bright state every few seconds while the other lamp in the fixture dimmed normally. The problem was showing-up in all twenty fixtures that were installed in the area. Since at least four different people had a part in the installation of different sets of these fixtures, a mis-wire was unlikely to be the cause. Because the the symptom manifested itself in all of the sets of fixtures, a bad lamp, ballast, or dimmer was also unlikely. Incompatibility seemed the most likely explanation. What was the cause and what was the fix?
The players (all for a 277V circuit):
- The Prudential Ltg. P-43 4″ x 4′ recessed fixture
- The Lutron Hi-lume 3D 28W single lamp ballast, using 3-wire line voltage dimming
- The Lutron Nova T single pole, fluorescent 3-wire line voltage, slide-to-off, 8A dimmer
- Two GE T5HO lamps
- The book of lighting submittals for the job
- Lutron technical support
The installation (shown in Figure 1 below):
- Each fixture contains two lamps.
- Each fixture contains two Lutron Hi-lume 3D ballasts, one for each lamp.
- Each Lutron Nova T dimmer controls two fixtures (or four ballasts total).
Figure 1
My first step was to verify that the lamps, ballasts, and dimmers were those specified in the lighting submittals. I am sure that many of you have seen the first problem I found from the lists above. As I removed the lens on the first fixture, I saw the 54W T5 HO lamps which I had installed as instructed by our project superintendent. I removed the lamps and then the pan which covers the ballasts. As I read the ballasts for information, namely the model number, I saw that these ballasts were rated for 28W lamps and not 54W HO lamps. ”Wow, this is going to be an easy fix,” I thought.
Next, I checked the lighting submittals book to see what was specified. The ballast was correct, but the lamping had been misinterpreted. A summary chart stated that each fixture had a total of 54W. The 54W number had been carried directly to the lamping number instead of being divided by two. As such, the lamps that had been ordered, received, and installed were wrong.
I found some 28W T5 lamps that were assigned to a fixture that we had not yet received. I had high hopes for this potentially simple fix. I replaced four lamps in the two fixtures which were attached to the same dimmer. I turned-on the luminaires to full brightness and then slowly lowered the dimmer. As I got to the 50% mark, I observed that one lamp in each fixture no longer abruptly changed between bright and dim. Unfortunately a new version of the same symptom appeared. Instead of a sudden shift in brightness, the lamp now displayed a slow oscillation, about one cycle per second, of a clean sine wave of dim to bright and back to dim again. The other lamp in the same fixture was just as before, dimming as it should. At this point, with the lamp output matching the ballast rating, it was time to move my attention to the dimmer and the wiring.
The Nova T is a simple, 3 wire, line voltage, sliding dimmer. Its capacity is 8A, so with 4 ballasts, we were no where near its maximum rating. We verified the model of the dimmer with the submittals, and they matched. We checked the wiring in the dimmer box, the outlet box in the ceiling, and in the fixture. Everything appeared to be in order.
With everything appearing to be correct, I called technical support at Lutron to enlist their aid. I explained the problem to the Lutron tech, giving him the model numbers of the ballast and dimmer. He stated that they are compatible and should work fine and also verified that the lamps should not be a problem. He had us do some routine testing to see if everything was working as it should as far as could be told and everything passed. I explained that we had verified the wiring. Next he had us spread apart the wiring and even had us move one ballast as far away from the other as possible. Nothing changed. At this point, he was at a loss and said he would forward the problem to their engineers. Once they had some ideas or found a solution, they would return the call.
In the meantime, I moved to other tasks on our punch list while I awaited for the call from Lutron. Two days later, the tech called back. He did not have any ideas for me, but asked a few more questions on behalf of the engineers. It was mostly a reiteration of what had already been said. He stated that he would contact me as soon as they found something.
The next day, our list of things to do was quite small, and I really wanted to fix this problem. I called a skilled and masterful electrician with whom I had worked in the past to see if he had ever seen anything like this before. He said that he had not, but he let me know that when he has seen odd problems in the past that manifest in multiple fixtures, it was generally one of two things: a bad batch of ballasts or the tombstones. He had seen entire batches of ballasts be defective and said that it was not beyond possibility.
The tombstones being the easier of the two to check, I focused on them. I knew that the two tombstones which belonged to each lamp in each fixture were wired to the ballast on that lamp’s side of the fixture, so I looked at the tombstones themselves. They had a good, solid connection to the wiring, but I noticed something with the ballast and tombstone wiring in general. Here is what I saw:
Why was it wired that way? I had absolutely no idea if that was the problem or not, but I was out of options. I reversed the blue and the red wires on one ballast so that the fixture looked like the following:
I turned-on the fixture to full brightness and dimmed it to 50%. I held my breath as I slowly lowered the dimmer to its lowest setting. When the dimmer hit the bottom, there was no oscillation to be found. It worked!
I do not know how or why it worked as I still do not know the technical cause of the problem. I spoke with the tech at Lutron a day or two later and explained what I had done. He did not understand it either, but said he would forward it on to the engineers. I have not since heard from them. I spent the next three hours switching the wiring on a single ballast in each fixture, and installing the proper 28W lamps.
Occasionally after implementing the wiring change, a fixture would show very slight symptoms of one lamp oscillating, but if allowed to warm-up for a slight bit before dimming, the oscillation would disappear after dimming. These lamps had not yet been on for very long (burnt-in or seasoned) which may be a contributing factor to this minor oscillation. GE’s information on burn-in is difficult to find. One piece of literature I read stated that these lamps were seasoned enough for dimming at the end of the assembly process and nowhere did I read a specific instruction to burn-in these lamps. That said, it cannot hurt, but that will be the task of those who complete the work as I have since left that job site.
Of interesting note, Lutron offers a single Hi-lume 3D ballast for two T5 28W lamps. Why that was not used over two separate ballasts I will never know unless they wanted some level of redundancy.
Summary:
- Always check your model numbers against your submittals.
- Your submittal book can be wrong, especially if they include summaries or charts of information from the submittals, or if they have not been kept up-to-date with changes. People at all levels make mistakes.
- Use the manufacturer’s or the specific part’s technical support.
- Use the resources of skilled electricians whom you know.
- Question why things are done the way they are. Although a specific installation may work in one hundred other situations, something about the current situation or manufacture may be the cause of the problem.
