what happens when 2 separate "hot" lines from same breaker get tied together

| I'm trying to wire some lights so that when either of 2 different situations | arise these particular lights operate. I have two separate switches on the | same breaker that go to their own device (one a soffit plug and the other a | motion light). What I want to do is when the soffit plug is hot I want | these new lights on and when the motion light is on I want these new lights | to be on, and of couse if both situations happen at the same time I want the | new set of lights to be on. I'm confident I have the wiring firgued out | barring this one possible glitch. When both "line" wires come into the | junction box and feed the one load wire what's going to happen?

The "glitch" you'll end up with is when either switch is turned on, then everything (soffit plug, motion light, and new lights) comes on. This is because when you join the two line wires in the junction box, you are effectively connecting it all together.

Had these been on opposite phases in a 2 pole center tapped feed, then you would have (hopefully no more than) 2 tripped breakers.

If you want a common light to indicate if any of other loads is on, then what you need to do is isolate them by having each switched circuit power a relay that has parallel contacts powering the new lights.

The other issue would be thermal heating if there are multiple neutral paths. You always want the same amount of current in the wire going out a hole in a metal box as you have returned on the neutral in that hole. Otherwise the box becomes an inductor. This might not be a problem in this installation but it is something to be aware of.

thanks,

what exactly would this relay be called if you could tell me.

John

What you need is a relay to separate/switch the circuits. This is real common in theaters and stage situations. For a show they want to shut down the exit signs, if there is an emergency they want the lights to come on immediately.

A standard ice cube would work depending on the load. Square D makes a CO3 relay that is I think 20 amp and comes with an NO and NC contact on it. Down side to this is that the coil is pulled in all the time. Eventually it will fail and you will only have one switch working. A latching relay would be better but then if there is no power you would not be able to switch from one source to the other. Go with the ice cube relay. 5 or 10 years from now you may have to replace it.

| thanks, | | what exactly would this relay be called if you could tell me.

A simple relay.

|> | I'm trying to wire some lights so that when either of 2 different | situations |> | arise these particular lights operate. I have two separate switches on | the |> | same breaker that go to their own device (one a soffit plug and the | other a |> | motion light). What I want to do is when the soffit plug is hot I want |> | these new lights on and when the motion light is on I want these new | lights |> | to be on, and of couse if both situations happen at the same time I want | the |> | new set of lights to be on. I'm confident I have the wiring firgued out |> | barring this one possible glitch. When both "line" wires come into the |> | junction box and feed the one load wire what's going to happen? |>

|> The "glitch" you'll end up with is when either switch is turned on, then |> everything (soffit plug, motion light, and new lights) comes on. This |> is because when you join the two line wires in the junction box, you are |> effectively connecting it all together. |>

|> Had these been on opposite phases in a 2 pole center tapped feed, then |> you would have (hopefully no more than) 2 tripped breakers. |>

|> If you want a common light to indicate if any of other loads is on, then |> what you need to do is isolate them by having each switched circuit power |> a relay that has parallel contacts powering the new lights. |>

|> -- |> -------------------------------------------------------------------------- | --- |> | Phil Howard KA9WGN |

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