# How to connect two circuits into on light bulb with a switch in each

I am not an expert. but I have two circuits, each on is 220v and both have a switch. I want to connect the two circuits into one light bulb. what I have to follow or need to know, To make this happens?

if any one of the switch turned on, the bulb goes on. and doesn't goes off, until all switches is off.

# UPDATE

THIS DIGARM IS JUST FOR CLARIFICATION NOT FOR ACTUALLY USE.

I did this to clarify what I mean. what I need to adjust to make this happen. I don't mind major editing.

simulate this circuit – Schematic created using CircuitLab

• Why do you have two circuits? Do they come from different breakers? If so, then you cannot join them. Jun 29, 2017 at 0:15
• @TonyStewart.EEsince'75 yes from different breakers. so you say it is impossible? or it is challenging ? Jun 29, 2017 at 0:32
• What this implies is shorting both sources. You can choose A or B or none But if A then not B and if B then not A, but not both together. This implies more logic and circuit wires with relays. How about a wireless switch? or re-route to share only ONE source with two remote switches and 3 wires+gnd. SPDT toggle light from either switch. Jun 29, 2017 at 0:40

As you said yourself, you should never directly connect two circuits together. But the behavior you want could be done with a relay:

simulate this circuit – Schematic created using CircuitLab

You can expand this to as many circuits as you want, as long as they are all isolated from each other with the appropriate relay arrangement.

Of course, if the directly-connected circuit (LINE 2 as drawn here) trips its breaker, then none of the switches will turn the light on, but you'll have that problem with any safe solution. Just choose which circuit should be the direct one and use relays for the rest.

AND CLEARLY MARK WHEN YOU BUILD THIS THAT THE RELAY'S CONTACTS ARE NOT FROM THE SAME POWER SOURCE AS THE COIL!!! This is important for the next person's ability to work on it safely.

simulate this circuit – Schematic created using CircuitLab

• This is what I thought the OP meant. Jun 29, 2017 at 2:56
• it's normally how it's done. But this may not be one of those situations. Sometimes we guess what they need, rather than assume he knows what he asking for is correct, which was apparently not. Jun 29, 2017 at 3:10

simulate this circuit – Schematic created using CircuitLab

Figure 1. Two switches in OR arrangement.

I have drawn the circuit on a 12 V supply. I recommend this as the maximum voltage you should work on as your question suggests that you are not qualified - never mind an expert - to work on higher voltages which risk electrocution.

• but this is two switches on one circuit (one source). how would you do it if you had two of +12v sources? and sw on each side Jun 28, 2017 at 23:39
• It could be hazardous to try this with separate power sources - with AC, you would get a short circuit if your two circuits happen to be on different phases. Jun 28, 2017 at 23:42
• @PeterBennett what are you mean by different phases? Jun 28, 2017 at 23:45
• This might not be what he's asking. I think two SPDT switches are needed. Jun 28, 2017 at 23:51
• @MikeWaters do you have suggestions? Jun 29, 2017 at 0:32