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I've run into a bit of a delema. I plan to install 16 Halo H7 recessed lights in the ceiling of a new home. They are technically rated at 75 watts because they have medium screw base sockets and can take 75 watt incandescent lamps. Normally, if I wanted to dim them, I would need a 1200 watt dimmer (75*16=1200).

But the dimable LED bulbs I intend to use are 5 watts each, so only an 80 watt dimmer would be required. The dimmer would need to be able to dim LEDs.

But I'm having a hard time finding an LED compatible dimmer that is rated for 1200 watts. (Probably because no one needs to put 240 fixtures on a single dimmer!)

I know that using a smaller LED dimmer would be safe and work fine for my application, but since this is new construction and must pass inspection, is there a code-complaint way to handle this scenario?

Is there a rule or exception that makes using a small dimmer in this case OK? Can I write "max lamp size: 10 watts" inside each fixture to derate it? Or should I just put a toggle switch on the circuit and replace it with an LED dimmer after getting the CO?

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  • The largest medium base incandescent lamps you can buy are 300 watts but you don't have to size your dimmer to handle 4800 watts. You only have to size the switch/dimmer for the load. If someone overloads the dimmer it will be damaged and stop working or trip the breaker.
    – ArchonOSX
    Commented Dec 21, 2017 at 9:48
  • If the fixture is rated for 75 watts, that's the wattage used for calculating the load of the circuit.
    – Nick
    Commented Dec 21, 2017 at 9:56
  • Check with the electrical inspector in your jurisdiction. Make sure that if he says it is OK to use a dimmer designed for your planned load that this is not a decision another inspector in his department would call the other way.
    – Jim Stewart
    Commented Dec 21, 2017 at 10:07
  • Labeling as you say seems a good idea regardless of whether it helps pass inspection.
    – agentp
    Commented Dec 21, 2017 at 15:28

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This ceases to be a factor if you use dedicated LED luminaires which don't have sockets. LEDs are so reliable, and they don't "burn out" like bulbs, that there is no reason to socket them and a lot of reasons not to - such as this.

This also opens the door to using more robust dimming controls like 0-10V, PWM or smart dimming. (The system you are currently angling for is "the old way of dimming" that is made for incandescents, and LEDs struggle to work properly because it works the exact opposite way LEDs do.)

If you really want to use those fixtures, you can switch their sockets to something like GU24 which do not support incandescents. However GU24 screw-in LEDs are notably more expensive. Candelabra sockets are readily available in LED at no cost disadvantage, but incandescent candelabra bulbs are commonly 40W and can be found as large as 60W.

If you really, really, really want to support incandescents, then use 2 dimmers and call it a "feature". However, you have other problems. This with the dimmers consumes more than 50% of a 20A circuit's capacity, so it must be on a dedicated circuit that serves only hardwired loads and does not power any receptacles. Like any continuous load, it must be derated 125% so this counts as 1500W toward hard circuit limits of 1800W (15A) or 2400W (20A).

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  • the actual reliability of LED's remains to be seen. I've had one fail at about 5 years (It was on 24/7). Better than incandescent, but its not like they last forever.
    – agentp
    Commented Dec 21, 2017 at 21:37
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    @agentp what make and model was it? Reliability is a totally different issue than bulb life. If you really, really want to buy a cheap LED that fell off a truck in Shenzhen with an onboard driver made with plague capacitors.... there are plenty of vendors falling over each other to part you from your hard-earned. But that hardly reflects on LED tech.
    – Harper - Reinstate Monica
    Commented Dec 22, 2017 at 1:27
  • was a phillips and i ran the numbers it lasted almost exactly its projected lifetime. Read the fine print, when they claim 20 years life its based on use only a couple of hours a day. Anyway its all good for a replaceable bulb, I just dont like the idea of replacing whole fixtures when they go,
    – agentp
    Commented Dec 22, 2017 at 4:01
  • @agentp you wouldn't need to, you'd only need to replace the electronic driver. That's what failed in your Philips too. The LED emitter is going to outlive all of us. I've got a cheap Cheese LED strip being powered by a 24V GE power supply built by their ballast division. It's been going 5 years steady on, not one of the 42 triplets has failed. Nothing to fail in those.
    – Harper - Reinstate Monica
    Commented Dec 22, 2017 at 5:29

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