[WarehouseShelly]

Hello! I've recently purchased a warehouse formerly inhabited by a carpenter. He installed what initially appeared to be a functional electrical system with a well-labelled breaker box. At some point, I noticed a hot dimmer switch and quickly realized that all the overhead dimmer switches heat up when all the lights are on. Turns out he's got 18 100W bulbs on one 20amp breaker and 24(!) 100W bulbs on another 20 amp breaker. The breakers have never blown, of course- just the wires getting hot.

All the lights are set in clusters of threes- six lights per dimmer. The wiring is all external (no walls in here) and encased in metal conduit (well fastened to the brick).

I'm hoping that I'll find 12 gauge in there, and I was thinking that we could add two breakers and run new 12 gauge to some of these branches... but I wanted to ask first. Is two enough to add? I'm wondering if we should switch the original breakers to 15amps... how many 100w bulbs we should allow for on each breaker... and if there are any considerations that I'm missing. Also, we're planning to switch to more efficient fluorescent lights- does this at all impact our load concerns? How worried should I be about other cables in the conduits having melted insulation due to the overhead lights?

Thank you so much for your help!
-Shelly

[bhayne]

Switching to 25W dimmable compact fluorescent bulbs will solve your problem with no rewiring nescessary(~$16 each).
You should look into a compact fluorescent that have plastic covers so they appear like normal bulbs (thus, not affecting the fixtures' looks).

[WarehouseShelly]

Switching to 25W dimmable compact flourescent bulbs will solve your problem with no rewiring nescessary(~$16 each).
You should look into a compact flourescent that have plastic covers so they appear like normal bulbs (thus, not affecting the fixtures' looks).

I thought that might be the case, but wanted to be on the safe side! What do you think about possible melted wire insulation, though?

[bhayne]

Heating will be most intense in the junction boxes where there are crowded wires, connections, terminations and dimmers (resistive elements). Actually, as you've already discovered, the dimmers are the weak link. The conductors are protected by the breakers.

Even a 20A breaker can supply 20A+ depending on breaker temperature (the trip unit is a heater). Just like conductors can supply more power when cool. If the conductors were getting hot enough to melt the insolation, you'd smell it (especially at the panel were conductors are bent and terminated) (at the dimmers you may smell the resistive element. Don't confuse that with the conductor insulation).

[tkrussell]

While I absolutely agree with converting to all CF lamps, just want to let you know that heat is to be expected.

Keep in mind that every incandescent dimmer will get warm, sometimes hot, and this is stated in the instructions of most dimmers. 600 watt dimmers have an aluminum plate designed to radiate the heat created by the dimmer's functions.

Larger dimmers have exposed radiator fins.

This is explained briefly at Lutron's FAQ and here. Lutron is a popular dimmer manufacturer.

A 20 amp circuit can handle and is rated 2400 watts, or 24- 100 watt bulbs, but needs #12 copper.

But more circuits will be a very good move. Most electricians would not put that much load on a circuit. Most of us derating even residential wiring 80 %, just to be sure there are no problems.

[WarehouseShelly]

Thank you both so much! Do either of you have a recommendation for which dimmable CFL brand to go with?

Cheers,
Shelly

[bhayne]

I was at a light symposium and GE had a good fixture. It was dimmable, had a plastic cover over the element so that it looked like a standard bulb and cost about $16 CAN.

I expressed my worries about the high price but if it saves you from rewiring, over-heating plus the energy savings (1/4 of the electric usage) as in your case, I would go for it. You may want to shop for a cheaper one.