Why do most smart light switches need a neutral wire?

  • Some manufacturers get around the "no neutral" problem by using the ground wire as a substitute. Such an example is the ODS10 by Leviton. The instruction manual even makes it clear that the occupancy (motion) switch WILL NOT WORK without connecting the ground wire. No ground wire connected means no power to the switch's motion sensor.
    – Tom D.
    Apr 4, 2018 at 2:54

3 Answers 3


Put simply; the smart switch contains electronics that needs power to operate, while a regular switch just mechanically cuts the load.

Regular switch:

Classic Light Circuit

Smart switch:

Switch wired with neutral

Source: http://www.vesternet.com/blog/2014/09/why-smart-switches-cant-be-used-without-neutral/

  • Good answer. Plain and simple.
    – user101687
    Jun 21, 2019 at 20:19

In order so that the switch can be 'on' to receive the RF signals, it needs a return path for itself so the 'load' isn't on all the time. Having the neutral wire present at the switch allows this to happen, and then when you command the load to turn on, it can pass through all the electricity to the load and thence back via that neutral wire to your load center.


What more important; what if you don't have a neutral and use a 2-wire module...

In those cases the smartswitch will be added to your electrical system in serial, instead of parallel. Because the smartswitch needs to be powered to be able to receive commands from the homecontroller, it cannot completely switch off, so it will always "leak" a certain amount of power. This power is not enough to be noticed on a regular light bulb (though on led lights it might show, as not being able to turn the lights completely off)

This is also the reason you see those devices (2-wire devices) only as dimmer modules, not as switches.

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