Dimming T12's in older school

[sw_ross]

Maintenance guy from the school called today to ask about some T12's that are on dimmers. The school was built in the early 80's. I haven't encountered this before.

The dimmers are dimensionally large because of aluminum heat dissipation fins. They probably take up the space of a double yoked device. They are manufactured with 4 wires coming out the back of dimmer, black, white, red, yellow.

The fixtures have a "MagneTek" dimming ballast.

Do these use a special type of lamp for dimming?

He wants to convert the fixtures to LED. I told him the easiest way would be to use a single pole switch and not deal with dimming. He's okay with that.

Is there anything I should be aware of in this type of setup? I'm assuming that from the switch box to the row of lights is going to be a switch leg and a neutral.

I haven't been there yet, I've only seen pics that he texted me.

Thanks!

 

[GoldDigger]

Maintenance guy from the school called today to ask about some T12's that are on dimmers. The school was built in the early 80's. I haven't encountered this before.

The dimmers are dimensionally large because of aluminum heat dissipation fins. They probably take up the space of a double yoked device. They are manufactured with 4 wires coming out the back of dimmer, black, white, red, yellow.

The fixtures have a "MagneTek" dimming ballast.

Do these use a special type of lamp for dimming?

He wants to convert the fixtures to LED. I told him the easiest way would be to use a single pole switch and not deal with dimming. He's okay with that.

Is there anything I should be aware of in this type of setup? I'm assuming that from the switch box to the row of lights is going to be a switch leg and a neutral.

I haven't been there yet, I've only seen pics that he texted me.

Thanks!

Not sure about the Magnetek specifically, but magnetic dimming ballasts for T12 fixtures are generally built to accept two AC inputs. One is a switched full voltage input which is used to drive the filaments via isolation windings while the other is a controlled AC input which is reduced in effective voltage to provide the dimming. Before the age of electronic dimmers, the control was a wall mounted variable autotransformer or Variac (TM) which had a minimum voltage limit stop to keep the lights from flickering combined with a microswitch which turned off power to both the variable and the fixed AC lines when the knob was turned to the lowest position. Our church, built in the late 60's, used those, and they are still in service with no problems.
The electronic dimmers you see probably have the same range-limited voltage output and a two pole switch to turn off both outputs simultaneously.

The black and white are probably the line inputs while the white-red and white-yellow circuits are (in some order) the full voltage and the controlled voltage outputs to the ballast.

Although you may not see the qualification in the specs for tubes these days, the original dimmer design was for 40W fluorescent tubes and for whatever reason stated that energy saving (36W or lower) tubes that were designed to draw less current from a standard ballast were NOT approved for use with those dimmers. The tubes also had to be compatible with Rapid Start operation that did not require the inductive kick of a separate starter module.

If the dimming function is at all useful for church purposes, you will have a hard time finding any better way to dim linear fluorescent luminaires. But changing the luminaires to modern smaller diameter tube units or LED units will save some energy in the long run. And LED units may be suitable for simple two wire dimming operation.
Luminaires with 0-10 volt dimming avoid the need for two power sources by controlling the dimming ballast with a 0-10V analog signal line and running only full voltage switched power to the ballasts.

 

[sw_ross]

Thanks for a little historical background on this setup. I have seen this style of dimmer used in a church that I did some work into (task was unrelated to the dimmers) and always wondered about how they functioned.

In this school, the description from the maintenance guy, there are about 50 fixtures that are controlled from a bank of about 4-5 of these dimmers. I don't know anything about the layout other than that. The school is gradually converting over to led and maint. guy ran into this situation and wasn't sure what the options are. He made it sound like they are accent lighting like an up light in a tray that is below ceiling height and maybe 8' off ground.

Can the 0-10v dimming be retro-fit into older housings? I haven't worked with 0-10 yet, but know that a low voltage 2-conductor cable is required. I think that trying to get the l.v. cable interconnected through all 50 fixtures and back to the switchbox might turn out to be more costly than the school desires. That's why I asked him about whether they needed the dimming feature or not.

 

[kwired]

Thanks for a little historical background on this setup. I have seen this style of dimmer used in a church that I did some work into (task was unrelated to the dimmers) and always wondered about how they functioned.

In this school, the description from the maintenance guy, there are about 50 fixtures that are controlled from a bank of about 4-5 of these dimmers. I don't know anything about the layout other than that. The school is gradually converting over to led and maint. guy ran into this situation and wasn't sure what the options are. He made it sound like they are accent lighting like an up light in a tray that is below ceiling height and maybe 8' off ground.

Can the 0-10v dimming be retro-fit into older housings? I haven't worked with 0-10 yet, but know that a low voltage 2-conductor cable is required. I think that trying to get the l.v. cable interconnected through all 50 fixtures and back to the switchbox might turn out to be more costly than the school desires. That's why I asked him about whether they needed the dimming feature or not.

Though the 0-10 circuit is low voltage circuit, I don't believe it is designated as class 2 control circuit, and therefore can (more like must) be run as class 1 control circuit if ran separately, otherwise run those conductors in same raceways/cables as the power circuits.

Add: your old system likely already has enough conductors ran from luminaire to switching locations.

 

[sw_ross]

Even if I have the conductors needed to do 0-10 dimming is it possible to retrofit an existing fixture to this?

Do they make dimmable led lamps that could use the existing tombstones and then be dimmed by a lutron dimmer?

 

[kwired]

Even if I have the conductors needed to do 0-10 dimming is it possible to retrofit an existing fixture to this?

Do they make dimmable led lamps that could use the existing tombstones and then be dimmed by a lutron dimmer?

LED replacement lamps are dimmed by a standard dimmer (or at least one rated for CFL/LED's) in the supply line, when they are "dimmable".

The 0-10 V dimming LED's will have the 0-10V leads on the LED driver itself, you will find this option on replacement fixtures but not on retrofit lamp tubes.