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My front porch overhead light fixture has two light bulbs, each of which has a positive and neutral lead. We have a two family house, and the porch is shared. Each of us has a switch in our house that turns on one of the two light bulbs. Each light bulb is on a different circuit. This works fine, but I need to replace the fixture.

Note, these are not three way switches to a single load. There are two circuits running to a fixture which has two sockets, each socket has a discrete positive and neutral.

I'd like to maintain the ability for us to control our lights individually, which would require a fixture with four leads (two per bulb). And I could just buy another, which would be fine.

But I am wondering if there is such thing as an "OR" switch that would turn on a single fixture/load if either (or both) of our switches are turned on, and only have it off if neither of our switches are on.

I could do this easily in the 12V DC world but this is 120V AC and an outdoor location so I don't want to hack this together.

Here is a picture of the current situation, after I removed the old fixture. enter image description here

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  • Whats wrong with a two-way switching circuit so either can turn both of them on or off. Commented Jan 14, 2023 at 2:25
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    Does each household have its own electricity meter? If so then you can't "OR" them into one point to power a single load. RMSman's answer is probably the best way to go - just find a 2-bulb fixture you like the look of and decouple the bulb holders from each other.
    – brhans
    Commented Jan 14, 2023 at 2:53
  • @RohitGupta it's not the behavior I want but more precisely, I don't want to touch the existing switches in each unit, it would be a big pain.
    – Jeremy
    Commented Jan 14, 2023 at 15:58
  • @brhans yes, and thank you for pointing that out.
    – Jeremy
    Commented Jan 14, 2023 at 15:58

2 Answers 2

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Almost any fixture with a 2 bulb setup will have hot and neutral from each bulb tied together to a single pigtail for the hot and neutrals, and a ground for the body of the fixture. You will simply need to remove the pigtails and you will have your separate hot and neutrals for each bulb.

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My front porch overhead light fixture has two light bulbs, each of which has a positive and neutral lead.

There's no positive. It's AC power.

I gather you have familiarity with 12 volt DC stuff from automotive electrical and the like, and you're going "well I can merge these with a diode!" No you can't.

By the way, neutral is not ground and it is not "common"/chassis. Houses are wired as an "isolated system" with all neutrals being run with their partner hot/live wires. The neutral must serve ONLY its partner hot/live because neutrals don't have fuses. What keeps a neutral from overloading? Nothing, expect that neutral current can't exceed hot/live current when everything is properly wired.

Properly wire.

We have a two family house, and the porch is shared. Each of us has a switch in our house that turns on one of the two light bulbs. Each light bulb is on a different circuit.

OK, that's a standard setup with multi-unit properties. Each light bulb in the fixture is fed from a different light switch inside the tenant unit, and powered by the tenant's electrical service that they pay for. That way you avoid a) tenant 1 paying for tenant 2's leaving the light on, and b) having a separate meter and billing just for commons loads, as is required in the USA.

This works fine, but I need to replace the fixture.

Well. That's tricky. You need to get a fixture which supports that feature.

If you think you're going to go "tra la la" through the furniture store or Amazon and go "that one" solely on aesthetics, afraid not. Finding the "separate bulbs" feature will be paramount.

But I am wondering if there is such thing as an "OR" switch that would turn on a single fixture/load if either (or both) of our switches are turned on, and only have it off if neither of our switches are on.

Like a diode if this were 12 volt wiring in a vehicle? No. You have two big problems.

First, what do you do about neutral? If you use one tenant's neutral then when the other tenant switches on the light, current is returning on the wrong neutral. If you connect both neutrals, you have a neutral loop. Suppose one flat has a problem with their neutral connection at the utility pole. Now the whole flat's neutral current will path through your little tie-in at the light! And that wire is not rated for that, and again, it's not fused.

Second, who pays? Even if you have tenant 2's light power a 12 volt transformer that picks up a relay inside tenant 1's switch box, now tenant 1 is paying all the power and that's not fair.

I suppose you could have tenant 1's switch be DPDT and switch both hot and neutral, when tenant 1's switch is off it connects the light to tenant 2's switch. That's the only legal option I can see.

Note that if tenant 2 is supplied a different phase of power, there will be 400 volts between tenant 1 and tenant 2's line/hot. The switch will need to be rated for that.

I could do this easily in the 12V DC world but this is 120V AC and an outdoor location so I don't want to hack this together

Well, there's an option. Have each tenant's switch feed a 12 volt power supply (so two 12 volt power supplies). Getting 12 volt fixtures is not a problem, look at RV lighting.

But other than that, everything you learned about low voltage DC is wrong about mains AC. AC is complicated and all the wiring practices are different.

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  • "AC is complicated" for me, it was like another world when I started to learn about it!
    – Thomas
    Commented Jan 14, 2023 at 10:44
  • Good points. I'm going to go with a two bulb fixture and keep things as they are. For the "who pays" option, in our case it's not a problem because it's family in both units, no one will care who pays for an LED light bulb, but if we sell the house, it wouldn't be an ideal setup for the next owner and might be downright confusing.
    – Jeremy
    Commented Jan 14, 2023 at 15:57

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