I read on the internet that a Smart Switch that does not require a neutral works via a hub because that's where it stores the credentials to the wireless network. This sounds like BS because you can just store the information on EPROM. A hub sounds similar to the Cloud servers that are used for all the smart switches that don't require a hub, but do require connection to the internet.

Also, for the smart switch to respond to the hub's commands, it would still need to be powered.

So do the switches have some sort of stored power supply, such as a rechargeable battery or a supercapacitor? If not, how do they work?

1 Answer 1


Whoever you're listening to on this is spouting technobabble

I'm sorry to say, but you probably should find a better source to read, as whoever's been feeding you information is spouting total nonsense. Whether a device needs a neutral wire or not has nothing to do with any sort of IoT contrivance such as a "smart home hub" and everything to do with how the device powers itself. As you have noticed, "smart switches" have electronics inside that need power to run, and they have to provide that power somehow; the same is also true for occupancy sensors, timers, and some, more sophisticated, types of dimmers as well.

However, old-school knob dimmers and plain toggle switches don't need such, and were often wired in a way that doesn't make neutral available at the switch box (the old way of wiring a "switch loop"), meaning that you can't put fancy things there unless they cheat. Some smart-switches are naughty (but UL approved to be a bit naughty due to the low currents involved) and return their supply current through the equipment grounding wire; this means they don't work in old houses without grounding, and also can cause problems downstream of GFCIs.

Others avoid this by returning their supply current via the controlled load (light, fan, or what-have-you) instead; while fan motors and incandescent lightbulbs don't mind having a wee bit of power trickled through them while supposedly "off", this causes LED lightbulbs to play up (either flickering periodically, or simply glowing dimly) as they are much more efficient (read: sensitive) than their incandescent counterparts. It also is problematic if you want to use the smart-switch to provide a control input to another control device, such as a relay, lighting contactor, or dimming power module, that has more "grunt" than the smart-switch, or provides a capability (such as multi-way switching) that the smart-switch doesn't have on its own.

Finally, there are a few wallbox devices that are battery-powered (some Intermatic wallbox timers are this way); this avoids the difficulties listed above, but obviously requires the occasional battery change in order to keep the device up and running. All of this is true no matter what sort of "smarts" (such as wireless capabilities, programming support, or what-have-you) the device has inside it, or whether it has any use for a hub or not.

  • Just an a small addition: these devices trickle current through the load when off, as you wrote. In addition, when on, even full bright if a dimmer, it still dims the load a little. The different between full power in and the dimmed power out provides the operating power for the device. Both of these effects can cause problems for some loads, which, along with cost of manufacturing, makes devices that use the neutral preferred.
    – DoxyLover
    Jul 24, 2020 at 5:48
  • They're not naughty; they're UL-approved to return current via ground. UL requires the current be very limited, both normal current and max possible malfunction current. Jul 24, 2020 at 6:05
  • @Harper-ReinstateMonica -- well, it's still naughty in principle, even if UL signs off on it :) Jul 24, 2020 at 11:39
  • Ha ha, Harp and 3ph are playing Santa Claus, determining who's naughty and who's nice! But seriously, I thought the 2017 (or maybe 2014) NEC didn't allow ANY return current on the ground anymore. Is there a conflict between a UL listing and the NEC? How coordinated are these outfits? Jul 24, 2020 at 16:36
  • @GeorgeAnderson -- The 2017 NEC's prohibition on smart-switches returning current via ground is only for new installations (replacement/retrofit situations in finished old work are exempt), and only kicked in on Jan 1 of this year. More broadly, UL has folks who sit on various NEC committees (as is typical for most NFPA standards), and they generally are pretty coordinated between the NEC and the UL product standards. (UL will still list smartswitch devices that return current via ground, though, due to their use in retrofit work.) Jul 24, 2020 at 23:00

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