So I read recently the US code is going to allow 10A circuits with 16g wire for dedicated lighting. With the lower consumption of LEDs I can see how this would make sense. Though, it would likely (IMO) mean either more used slots in the panel OR more complex circuits that spanned several rooms. Fine until you need to work on something.
Something I’ve been wondering about: Would it be more efficient to have a slot in the panel that runs a transformer and then service the lighting circuits directly with 12v (?)? AIUI, most residential lighting LED bulbs are converting the 120VAC to DC internally. I would assume it’s more inefficient to do this at dozens of individual points of use, and likely more expensive too. I would think it would also require less heat management in the fixtures if the bulbs didn’t need to have transformers running in them…? As many are probably aware, this is basically how most doorbells work.
So could you run a whole house on one or a few 12VDC circuits and then eliminate the need for transformers in every fixture? Would this be more or less efficient? Other thoughts on this? I believe low voltage wires require less care from a fire protection perspective as well (for instance, I don’t think boxes are required)
You’re not nuts, but it’s probably pretty impractical. This would make more sense in an off-grid home, and in fact it’s commonly done. The problem with doing it in a conventional house is the vastly smaller choice of lamps and fixtures that will run on 12V DC. You might be surprised to know that most “A” base LED lamps (the standard screw-in type) don’t run on 12V internally. For better efficiency, they run on much higher voltages, like 30-65V or more. So trying to power them with 12V isn’t going to work.
In my house, built in the 1950s, the ceiling lights run off a single circuit and wire loop, while the wall panels in the bedrooms run off a single circuit and wire loop. I don’t see why running a 10 amp loop for ceiling and other built-in lights would be any more complex.
My (limited) understanding is that low voltage requires larger wire sizes and generates more voltage drop/distance. Hence Tesla’s push for 48 volt architecture where the wiring harness can be ribbons like you see in a printer. I’m happy to be educated, however. Given the cost of copper, any increase in wire size is pretty expensive. There’s a reason the rest of the world is on 240V and standard overhead power is 14.4KV.
Yes, Tride has it right: dropping the voltage from 120V to 12V would require increasing the copper wire to 10 times the size to provide the same wattage. The increased cost of the copper wire would likely wipe out any savings. To say nothing of the increased cost to have electricians install 2 sets of wiring, 120V AC & 12V DC, running thru the whole house.
Regarding proposed #15 wire being allowed for lighting circuits, this could cause some increased risk. It assumes that those circuits are used only for low-wattage CFL or LED lightbulbs. But what if the resident is out of them, and dig deep into the closet and finds an old incandescent 100-watt bulb? And because they don’t want to sit in the dark, they install that in the #16 lighting circuit. There should be enough safety factor in #16 wire to handle this, up to about 7 or 8 incandescents, but it is an increase in risk. And what about someone using a light socket adaptor to plug an extension cord into that circuit? (A neighbor currently has one in use, to plug his Xmas lights into his porch light.)
I sort of, kind of did something like this at my last house, where I lost power several times a year and was looking for an alternative to a generator and transfer switch. I was gifted a couple deep-cycle lead acid batteries, which I set up in the bottom of my utility room closet with a float charger. I then installed three 12 VDC outlets in the house using 12 AWG NM cable. (As I recall, the 12 VDC receptacles, which had standard cigarette lighter outlets, were surprisingly expensive. At least, the nicer ones were.) I put in-line fuses for each outlet.
When my power went out, I just pulled out my 12 VDC lights, which included LED drop lights and a few other types, and plugged them in. I also had the usual portable TVs with lighter adapters, USB chargers, and even a 12 VDC fan intended for an RV.
The biggest advantages to me were that this avoided the losses associated with using an inverter and that I didn’t have to worry about the inverter shutting off when the batteries dropped to some magic number. Most of the time, everything continued to work down to about 8 VDC. Given time, I might have permanently installed some discreet 12 VDC RV light fixtures, but I ended up moving when I got married.
(Yes, I had a small fan for the closet. Not much, but likely enough.)
This is true as far as it goes, but is IMO irrelevant.
Right now, whole house wiring for incandescent illumination of a good-sized US house requires wiring sized to handle thousands of watts of total load. The same house lit only with LEDs would be dozens of watts. You could damn near wire the whole house with telephone gauge wiring. Which would be a massive reduction in volume of copper and wiring cost. Not an increase.
I expect the eventual end state is we have a lower voltage lower wattage distribution system in houses for lighting. None of which has a lamp base that a 120V incandescent will fit. Kind of like how we now have 120V electrical outlets that include 5v USB ports. There’s no way to plug a 120v incandescent bulb into the USB. And there’d be a separate 120/240v distribution to only the kitchen, the garage, and a GFCI in each bathroom for e.g. hairdryers ; nothing else.
But it’ll be the work of 20 more years to make that common in new construction, and we’ll be dealing with legacy 120v Edison base fixtures and hence bulbs for a long time.
If you think about it, the current crop of CFLs and now LEDs are themselves hermaphrodites designed for backwards compatibility into fixtures designed for 120v high wattage incandescents. They could be smaller, lighter, cheaper, and run cooler and longer if they didn’t each have to have that big screw-in base and that disposable power supply installed in their base.
Likewise all the labeling of bulbs as e.g. “100w equivalent”. It’s almost time to start labeling CFL/LED bulbs primarily, or only, in terms of lumens, not backwards-compatible watt-equivalents.
In the UK (with 220 volts) we have always had a separate 5amp circuit for lighting. Until relatively recently, it didn’t even need an earth. The standard is 1mm² (18awg) two-core-and-earth cable, but particularly long circuits can use 1.5mm² (16awg) cable.
When I was a student I lived in a one-room flat where the landlord charged high rates for metered power. The single ceiling light was free though, so I bought an adaptor to plug into that and I could run a 1kw heater or and iron that way.
We used to run old fashioned 60watt and 100watt bulbs everywhere, and in my house now, I have ceiling fans in all three bedrooms and two on the ground floor.
As an aside, it is now normal for all wall outlets to incorporate one or two USB power sockets.
Besides wiring a transformer will be necessary to use the AC supply. Transformers inside an electrical box at the light switch might be the place to do it. Existing wiring could be used for the low voltage on dedicated lighting circuits to retrofit existing homes. Most homes already have some type of voltage reducing transformer for doorbells, outdoor lighting, and thermostats. The lower voltage AC available from those could also be run with lower gauge wiring out to inverters closer to the lighting. The options are there, and I’d expect before long residential lighting circuits will be wired for low voltage DC, and common AC outlets will have USB type connectors for lamps and battery powered devices.
I think you’re all underestimating the time it takes in practice to actually change over a system like this.
In new construction, knob and tube wiring was replaced 75 years ago. Yet we still have millions of homes in the US with knob and tube wiring installed, and working every day. It’s being pulled out and replaced as homes are renovated & remodeled, but that is a slow, long-term process. Much of it happening as homeowners age and move into retirement or nursing homes, and their houses are sold – the new owners (or their insurance companies) demand that this wiring be updated. It takes decades for that process to be completed.
We may move to newer wiring systems in houses, but it won’t be a speedy change. (Also depends on all the makers of CFL/LED lights, portable appliance chargers, anything that uses a wall-wart agreeing on a standard outlet replacing the Edison screw socket.)
We used these throughout our house. Easy, cheap, good. No bulbs. I see this as the new normal. 10.5 watts each, so a 16AWG circuit would be just fine. Switchable color temp–what’s not to like?
Not going to work. Doorbell and HVAC 24V AC transformers typically have a power rating of 15-30VA (volt-amps, roughly equivalent to watts). One could power maybe one or two 60W-equivalent LED lights after subtracting what the doorbell/HVAC needs.
LED lights will always have to have a constant-current driver co-located with the diodes - you cannot just hook up the bare diodes directly to a DC supply (they’ll fry). Possibly they’ll get more efficient when run from DC, but IMO the main improvement will come from not having to cram them into an Edison-base bulb shape. Waste could be reduced if drivers were standardized somewhat so they could be more easily swapped out when they fail, instead of having to replace the entire light.
Sorry, meant a transformer like that, providing lower voltage AC, could be used to distribute to inverters closer to the lighting. However, I’m not sure there’s any real advantage to that now.
I wrote that we might have low voltage wiring installed in new construction in 20 years. That does NOT equal “there will be no legacy 20v lighting installations remaining”.
As you say, there are lots of knob and tube installations remaining 75 years after the last new one was installed. But from the date that non-knob and tube became the standard until new houses were being built with that new standard was just a couple of years.
Said another way, you’ve given a correct answer to a question nobody was asking.
Note that dedicated 12V lighting is already commonly in use both in landscape lighting (where the 12V power cable can be buried in a shallower trench than needed for 120V power cables) and in track lighting.
My go-to reference on DIY home renovations, the Holmes on Homes series, tells me that there are plenty of unqualified amateur electricians out there who are willing to overlook basic code requirements. As a result, wiring with lower-capacity wires invites those who disrespect codes to add to a circuit unaware that it would not support the same basic power levels as current homes. (Not just those using cheaters to feed appliance power off the lighting sockets)
As I understand my house wiring, a room may have the lights and outlets both fed off the same circuit - so circuits are area-specific rather than use-specific (except GFCI runs). Is there really that much savings of copper volume in running all the lighting on a separate smaller wire? That then means two, not one, separate run back to the breaker panel. (Although several rooms may be doubled up, as pointed out) Worse, pop one breaker and all the lights go out.
I agree though, I suspect as LED tech evolves there will be a standard separate connector and wiring for those devices.
However, the rule of thumb for anything has to be that it presents a significant jump in something - convenience, productivity, price - over existing. Quadrophonic was slow to catch on, because stereo worked fine. DVD replaced VHS because it was a huge step up in convenience; DVR features replaced VHS too because of convenience. Streaming/on demand so far is replacing DVR and DVD. Flat screen replaced tube for video because it was bigger, better, (and now) cheaper.
So what’s going t be the appeal for a dedicated LED circuit system? Will the wiring (in new homes and renvoations) be cheaper? Will the bulbs themselves be significantly cheaper? (Also note that the lifetimes of CFL and now LED mean much less turn-over in replacing existing bulbs…)
If I had to guess, what’s going to be a major innovation would be integrating whole home control into the circuits - with features like Google or Apple’s home control programs being able to control down to the individual element, monitoring as well as controlling. “hey Siri, turn on the deck lights and show me on the basement TV what’s crawling around in my yard…”
Filament-style LED bulbs run at close to line voltage; 120 or 240 V. They do so by just having dozens of tiny LEDs in series.
12v is a terrible idea for lighting. As andrewm said, you still need a power supply in the bulb, or at least a current limiting device. These also get cheaper as the voltage goes up.
Whatever overall wattage you have, it’ll be cheaper and more efficient to run at a higher voltage. If someone was going to come up with a lighting-only power distribution system with custom and deliberately incompatible connectors, they should go with 240v, not 12. And probably stick with AC.
