208V Lighting Circuit Through Single Pole Relay

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strap89

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Say you have a 208V lighting circuit but you only have access to a single pole relay as part of a larger lighting control system. The circuit is protected by a 20A/2P circuit breaker. It seems to me like it is permissible to only control this circuit with a single pole relay because its not a lamp holder and the relay would not indicate that the circuit is "off" like a toggle switch. 420.93 seems to apply to screw in style "lamp holders" with the concern being someone flipping a local switch and thinking there are not present hot wires. Does not seem to apply to a relay panel.

I know this is commonly done for for HVAC controls, just not certain if there is something I am missing specific to lighting.

Thanks
 
You are correct. 208/240V circuits must have protective and isolating devices on both lines, but control devices don’t matter (unless like you said, it’s a lamp socket). Perfectly legal, just not a really great idea though. Good electricians know better than to “trust” a circuit control device for safety, we test-verify-test. But a LOT of DIYers do not do so. There are numerous YT videos I have seen where the poster says to simply flip a toggle switch to “make the light circuit safe”. I can foresee that kind of thing happening here.

This by the way is done all the time in heating controls. It’s even done on 3 phase devices where they only control 2 of the phases, the third is left connected all of the time. So again, perfectly legal, just not “best practice”.
 
Can you use your lighting control relay to operate a two- or three-pole contactor? As Jraef said, it's not best practice to switch only one of the hot legs in a 208V single-phase circuit, even if permissible.


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