I want to control a light with two switches, but not a three way

Question

Not a traditional three way switch, but I want if either switch is on, the light comes on. Both switches have to be off for the light to go off. If both switches are on, the light should be on - but not over powered.

Answer 1

The key issue is that all current flowing in both directions (e.g., hot and neutral, but can also be hot and switched hot, etc.) must be in the same cable or conduit. With a traditional 3-way, you have two travelers, with at most one hot at any time. However, for this setup you can do the following:

• Power from panel 2-wire cable to first switch, 3-wire cable between the two switches, 2-wire cable to light - the same basic setup (but different connections) as an ordinary 3-way switch

First switch box:

• Black (hot)/white (neutral) to first box
• Black connects to both switch 1 and the black wire in the 3-wire cable
• White connects to the white wire in the 3-wire cable
• Second connection on switch 1 connects to red wire in the 3-wire cable

Second switch box:

• Black (switched hot)/white (neutral) to light fixture
• Black connects to both switch 2 and the red wire in the 3-wire cable
• White connects to the white wire in the 3-wire cable
• Second connection on switch 2 connects to the black wire in the 3-wire cable

With this configuration:

• White is always and only neutral (that is generally the case with new 3-way switch installations because of the relatively new requirement for neutral in switch boxes, but not always the case in the past)
• Black in the 3-wire cable is hot but only powers the light if switch 2 is on
• Red in the 3-wire cable is switched hot and only powers the light if switch 1 is on
• If both switches are off, the light is off
• If switch 1 is on, red becomes hot and powers the light, with red and white equal/opposite current
• If switch 2 is on, black carries current through to the light, with black and white equal/opposite current
• If both switches are on, black and red nominally carry 50% of the hot current each and white equal/opposite current. But if there is any imbalance between black and red they still balance white in total. Because all 3 wires are in one cable, this is code compliant no matter how much current is on red vs. black, similar to a double-switch fan/light.

Answer 2

Lets change the scenario to something that is a common design problem. Sometimes we have a Men's and Women's Bathroom with a common exhaust fan. Your logic be the same as your question.

• Sw1 on + Sw2 on = On
• Sw1 off + Sw2 on = On
• Sw1 on + Sw2 off = On
• Sw1 off + Sw2 off = Off

If you use 2 SPST Sw's you can run the line side of the circuit to matching posts on Sw1 and Sw2. Then run the switch leg from each switch to the exhaust fan and connect them together pigtailing it to the exhaust fan. The important part is that the fan and switches must be fed with only one circuit. In effect you are paralleling two start switches.

Hopes this helps.

Answer 3

I think everything's already been covered above, but it's very simple and you just need two 3-way plug-in wire clamps to split and combine the wiring to and from the switches:

I'm unfamiliar with the wiring color code used in the US, but for EU it would be:

• Phase up to switch: brown
• Switches to light: black
• Return/neutral: blue