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I have a 3-contact switch like this. enter image description here

As you can see, the switch doesn't have an OFF position, it diverts the current either between middle and left, or middle and right contacts.

Had to attach it to a wall lamp that didn't have a switch, by drilling a hole in the base of the lamp:

enter image description here

I have therefore one contact that I am not going to use and where I don't want current to flow at all. I cut it off and rolled all over the switch body in the place with 2 layers of insulating tape. The remaining 2 contacts were rolled in a layer of insulating tape as well, after connected to incoming live (middle contact) and lamp live (left contact) wires respectively.

As I drilled the hole in the base of the lamp, it turned out that the side of the switch with the spare contact may be touching the drywall a bit.

The question: since the current is supposedly trying to go from middle contact to the spare contact when lamp is turned off -- is it liable to cause problems such as heating up its insulation or similar -- simply by being live?

I am grateful and have upvoted all the three current answers, each of which provides relevant points for me. I feel that all three taken together answer the original question practically fully, but since I can only accept one, I gather I should accept the one, which most directly addresses the original question.

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    Does this lamp fixture actually bolt up to a proper junction box such as a pancake or octagon box? Is this low-voltage lighting? – Harper Sep 15 '18 at 20:30
  • @Harper this lamp is 220v fixture I connected to the 220v wire that goes under drywall to the fuse box. All the work on wiring was done by an electrician just a month ago. I am just attaching a kind of lamp that needs to have a switch near it, as I forgot to specify that there should be a switch in the wall for this wire, when the wiring work was done. The lamp itself mounts on a bracket that is attached to the wall. – Gnudiff Sep 15 '18 at 20:38
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    Wait. Latvia is in the EU. Has your country harmonized to EU electrical codes yet? Was this permitted/inspected? Or did you get some cranky old Soviet era guy who's still doing it the old way? EU codes don't exactly match North American codes, but they both agree on the major points. #suspicious of bad work – Harper Sep 15 '18 at 20:51
  • @Harper no idea on harmonisation level. Outlet for plug/switch will have a standard box, but any wires from switch to the fixture will just end in a wire coming out of the wall to be attached to the fixture which will be mounted directly on wall /ceiling. I have never seen it done differently since independence regaining either. I don't think the electrical code is required to be harmonised to that level of detail, as it is probably more of an internal issue in the country. The materials and fixtures must be EU approved though (and are mostly imported from other EU countries anyway). – Gnudiff Sep 16 '18 at 4:35
  • By wire I mean a cable of course. The outer insulation is stripped and wires exposed only at the point of connection. – Gnudiff Sep 16 '18 at 4:55
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The lamp appears to be made from metal. You need at least two insulation barriers, or protective earth, for this to be anywhere near safe or legal. The protection mechanism - and implications are slightly different.

Protective earthing means that the chassis of the lamp has a robust connection to PE of the electrical wiring, so any fault current will pass trough the PE conductor, with low enough resistance that no dangerous fault voltage will be present on the apparatus. It may additionally trigger ground fault devices, if such are fitted in the system.

Double insulation means that the chassis is not grounded, but you have two protective barriers between the user and the live current. If either one fails, there is no risk of electrocution. One device in this instance may be approved heat shrink tube over the contact terminals. The other insulation barrier may be secure fitting of the switch in such a way that it will not touch the chassis.

Electrical tape is for temporary fixes. It's not a permanent solution.

  • The lamp metal body has a factory-prepared grounding connector, which I connected to cable ground, so from that perspective I understand it should be OK – Gnudiff Sep 16 '18 at 15:16
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You can use the other contact not the common for the hot and then there would be no connection to the other contact point when the switch is in the off position but will work just fine just switch the hot to the other contact and the load to the common and you don't even need tape on the other side.

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    Ed Beal, brilliant. Hot power in one end contact, energizes middle contact when switched "ON". Other end contact never live. @Gnudiff, start un-taping. – Jimmy Fix-it Sep 15 '18 at 23:01
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The middle or spare contact won't heat up anything as long as no current is flowing, even when it is live and contacting the wall (which is usually not a conductor).

However that does not guarantee that your installation is safe and code-compliant. What I would worry is that when current flowing through middle-left contacts when the light is on, the heat generated at the contact point between your wire and the left contact would downgrade your electrical tape and compromise its insulation.

  • How is it supposed to be solved in normal cases for a switch like that which has exposed contacts? – Gnudiff Sep 16 '18 at 4:37
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    @Gnudiff Using wire connectors like this. Very commonly used in daily electronics, e.g. microwave, blender etc. – user12075 Sep 16 '18 at 17:04

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