I've inherited the wiring shown below. The two dimmers on the left operate separate lights, but I notice the L1 from the middle dimmer is connected to the Com on the left dimmer. Does this mean that the middle dimmer is wired the wrong way around? Should the daisy chaining of the incoming live wire not be from Com to Com?

v-pro dimmer switch

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    I would think so, but power is AC so sometimes you can get away with it. Do the lights work? What made you open this up? Commented Jan 1, 2020 at 16:19
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    Also if anyone is spotting the bad CE logo, the company seems to be legit and one of the major UK-based builders of dimmers. Commented Jan 1, 2020 at 16:22
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    I opened it up because I'm replacing the faceplate. Lights do work, but I want to make sure I'm replicating something done correctly.
    – Tim
    Commented Jan 1, 2020 at 16:57

1 Answer 1


I do believe it is wired backwards. That would never be tolerable in a DC (direct-current) system.

However, AC reverses 100 times a second (giving 50 full cycles per second). A funny side-effect of that is that some things don't care about being back-fed, e.g. breakers.

If your dimmers are one of those, then you got lucky.

However, I would expect that such a direction-agnostic dimmer is not very LED friendly. It's really past time to upgrade to LED lighting. They have been quite good for several years now. The power bill alone will pay for the dimmers inside a year.

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