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Most smart (WiFi remote) light switches available online say "neutral wire required". For example, this Gosund dimmer. In some older houses, this requirement for a neutral in the switch box is problematic. (I understand the NEC has been updated to require a neutral in switch boxes for new construction. Cool.)

Reading online, I found this NEC quote:

2017 Code Language:

N 404.22 Electronic Lighting Control Switches.

Electronic lighting control switches shall be listed. Electronic lighting control switches shall not introduce current on the equipment grounding conductor during normal operation. The requirement to not introduce current on the equipment grounding conductor shall take effect on January 1, 2020.

Exception: Electronic lighting control switches that introduce current on the equipment grounding conductor shall be permitted for applications covered by 404.2(C), Exception. Electronic lighting control switches that introduce current on the equipment grounding conductor shall be listed and marked for use in replacement or retrofit applications only.

My understanding of the exception above is that allows for replacement or retrofit smart switches which use a ground rather than neutral to power the electronics. Have I got that right?

Are such retrofit devices available? Listed?

P.S. I understand the listing requirement to be satisfied by an ETL listing, such as the Gosund seems to have.

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    A switch can be smart without having WiFi. Teeny tiny microcontrollers use very little power. Any radio adds some power requirements. Relatively speaking, WiFi adds a large power requirement. I don't know the specifics, but among the requirements by UL for making use of ground is a severe limit on the power sent over ground. – manassehkatz-Moving 2 Codidact Dec 6 '20 at 1:30
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    OK, @manassehkatz-Moving2Codidact, that sounds right. I found articles saying a typical WiFi smart outlet consumes about 1W. If powered from line and ground, that would be about 8mA current on the ground. A household "class A" GFIC trips at between 4-6mA. – Burt_Harris Dec 7 '20 at 18:41
  • From what I read a while back, it isn't even "one device below GFCI trigger" but actually designed so that multiple uses of ground-instead-of-neutral could be done without triggering GFCI. So we are talking about very low levels of current. That does not mean can't be "smart", but it may rule out direct WiFi. A hub of some sorts that communicates via powerline or Zigbee or similar to switches could in turn have a powered WiFi transceiver to let you have internet/intranet/smart phone/etc. control. – manassehkatz-Moving 2 Codidact Dec 7 '20 at 18:44
  • Understood. If you post it as an answer, I'll mark it accepted. – Burt_Harris Dec 9 '20 at 20:41
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I see nothing in the installation instructions that indicate that it is listed or "marked for use in replacement", the instructions show a neutral connection, and do not show what to do when the neutral is missing.

Occupancy sensors that satisfy the requirement like the Leviton ODS10 state "intended to replace a standard light switch" and the instructions show connection without a neutral and indicate it "requires a ground wire to operate".

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  • I agree the Gosound I provided is NOT mark for use in replacement scenarios only, my question is are there smart switches that are so marked. The Leviton ODS10 doesn't seem to be a smart-switch in the sense of being controlled over WiFi or similar. – Burt_Harris Dec 6 '20 at 1:04
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    Found a Leviton note saying that seems to indicate all their WiFi controlled models require a neutral: decorasmartsupport.zendesk.com/hc/en-us/articles/… – Burt_Harris Dec 6 '20 at 1:11

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