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Switching high voltages with arduino and a relay

  1. Sep 12, 2017 #1

    I came across this video on youtube where a guy was switching a lightbulb on and off with an arduino and a relay ().
    I was bothered by how he left out the phase wire (look at the image at 4 mins and 53 sec in). People mostly seem to be complaining about how he is breaking the ground wire, and I can see why that is wrong too, but shouldn't he also be using all three wires aswell? Even if he was breaking the phase wire and left out the ground wire then wouldn't it be unsafe to use this "adapter" with appliances that need to be grounded? If I were to do this then I would try to make the adapter like an extension of the wall outlet by connecting all three wires in both ends and breaking the phase wire, that way you could use it for appliances that are either grounded or not. Am I right or wrong?

    Also, I saw another video of a guy who was switching a light bulb on and off in the same way and he was using a plug that looked kind of like the 2 prong euro plug (he had wired it up himself). To do this safely, you would have to look for a lightbulb/socket that are double insulated right?

  2. jcsd
  3. Sep 12, 2017 #2


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    Didn't watch the vid, but yes, you want the phase to be the only one interrupted. Everything else should be as if this 'switch' is not even there. In the USA the neutral is NEVER EVER supposed to be interrupted. And of course the ground is the same.
  4. Sep 13, 2017 #3
    What @Averagesupernova said. The 'hot' wire should be the only one switched.

    Another thing ... the presenter stated 10 amp contact ratings at 120V and 240V AC voltage, and 10A at 28V and 30V DC. This is true for resistive loads (1), but contact rating is 3 amps for inductive loads. The small fan in the video should be low current and under the 3 amp rating, but even so, switching inductive loads reduces contact life, and it is a good idea to look closely at the SRD-05VDC-SL-C relay specifications.

    (1) For form A contacts. Couldn't make out the relay part number in the video, but it was SRD-05VDC-SL-C in a photograph I found online describing the HL52S relay board. Current rating for form C contacts is 7 amps at 240 VAC and 28 VDC.
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