Light switch wiring on old (1926) house


Old 07-24-16, 09:19 AM
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Light switch wiring on old (1926) house

Help! I'm trying to add a the monoprice zwave dual relay module ( to two light switches in my house. Of course, my house was built in 1926, which means nothing here is ever easy.

Here's my problem: I opened up the outlets, and the wiring doesn't make much sense to me.

Switch one (far right, first photo below) has four wires - a red and black at the bottom, and two whites going to the same screw at the top. This is a 3-way switch. From what I've read, these relay modules can be installed on some 3-way switches, so I wanted to try it here.

Switch two (middle of three outlets in photos, second photo below) only has two wires: A black and a white. And the white is coming from switch 1 (one of the two wires at the screw at the top), not the wall, which really confuses me.

Right now, here's my best guess: Black wire on both switches is live, white wire on both switches is the load (and these two switches share a load - not sure if that's actually possible), and red wire goes to the other switch for the 3-way. And the wiring is just old enough that there is no ground.

Does this make sense? Any other explanations? Is it possible to use the monoprice relay without a ground, or am I screwed?

thanks, Josh

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Last edited by pcboss; 07-24-16 at 09:46 AM. Reason: Switch was outlet for clarity
Old 07-24-16, 09:58 AM
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That module does not appear to need a ground, but it does need a neutral, which you may not have in these boxes.

I suggest you call switches switches, to avoid confusing folks who are used to calling receptacles outlets...

I also suggest you obtain an inexpensive analog multi-meter, if you don't have one, so you can identify which wires are hot, neutral, and switched.

The general convention is that white wires are neutrals but with switch wiring, white wires are often used as hot or switch hot and this is confusing to many; hence the need for a meter. White wires connected to a switch the ways yours are, are not neutrals. White wires used as hots or switched hots are supposed to be marked with black or colored tape or paint to indicate they are not neutrals, but this was not always done. Some of yours appear to be marked, but they also may be taped to repair old insulation.

You need to be gentle with those old cloth covered wires; the insulation gets very brittle with age and can easily crack or crumble. Heat-shrink tubing is handy for repairing failed insulation within the box.

A sketch showing all the switches, showing which control the same load, and with wire connections shown and labeled will help us guide you....
Old 07-24-16, 10:17 AM
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I don't know where you read something about connecting to three way switches but it's not shown in the wiring diagram.

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Will you have enough room for the module ?

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