Relay for 3 way switching with 2 wires

[K8MHZ]

The second switch would be added, therefore 2 or 3 or 10 conductors is not a problem for that one. The existing switch however has 2 wires only. Conclusion: first switch needs another conductor to become a true 3way switch rather than added complexities of other methods. Thanks everyone!

All you need to do is pull three wires from one switch location to the other. Two will be for travellers and one will be the common. That puts the 120 volt feed, the light leg and both commons all in the original box. In that box, connect the 120 feed to one common, the light leg to the other, and the two travellers together.

 

[K8MHZ]

Like this:

 

[kwired]

Typical latching relay still has a latch and unlatch coil, so a separate input for on and off are needed - meaning one common and two returns from switching stations.

The mentioned alternating relay would work.

Old low voltage lighting relays were essentially an "impulse relay" that reversed state every time the coil was energized, that is about what a typical alternating relay is, other then it likely has a double throw contact.

 

[K8MHZ]

View attachment 17155

I still don't see the problem.

Bob?

:happyyes:

 

[K8MHZ]

This is more like the OP's deal. Edited with MS paint.

View attachment 17156

 

[K8MHZ]

And, if the OP has the light fed and no neutral (white taped black), here is the diagram for that:

 

[justin13me]

And, if the OP has the light fed and no neutral (white taped black), here is the diagram for that:

Thx K8, you're getting off topic though. Most of us know how to wire 3ways. I'm trying/ was trying to use a regular contactor or relay w NO, Common and NC in between 2 single pole switches

 

[wwhitney]

I still don't see the problem.

Perhaps the existing light switch is very far from the light, and the new light switch will be very close to the light.

Cheers, Wayne

 

[K8MHZ]

Thx K8, you're getting off topic though. Most of us know how to wire 3ways. I'm trying/ was trying to use a regular contactor or relay w NO, Common and NC in between 2 single pole switches

Why, may I ask?

I guess I was under the impression you thought you were trying to use the relays to solve a cabling issue. What other reason would you have to want to use a relay?

 

[justin13me]

Why, may I ask?

I guess I was under the impression you thought you were trying to use the relays to solve a cabling issue. What other reason would you have to want to use a relay?

They're opposite ends of a big warehouse and the existing (LV master) switch only has a 2 wire going to it. Trying to think outside the box but our solution now will be to run a new 3 wire. Still working on the relay option though w 2 relays now. Hope to have a wiring diagram and solution up soon.

 

[K8MHZ]

They're opposite ends of a big warehouse and the existing (LV master) switch only has a 2 wire going to it. Trying to think outside the box but our solution now will be to run a new 3 wire. Still working on the relay option though w 2 relays now. Hope to have a wiring diagram and solution up soon.

So you are trying to save cable by wanting to go from new switch to light, instead of new switch to old switch?

 

[justin13me]

It's more about the theory now. Also I have an assortment of relays etc

 

[K8MHZ]

It's more about the theory now. Also I have an assortment of relays etc

One thing I did wonder was if you were trying to use a $40 relay to replace a $3 switch.

One thing to consider when designing 24 volt systems. The voltage drop on 24 volts is going to be 5 times greater than on 120 (given the same load), so switching the 120 volt side makes more sense in a large warehouse. Make sure your prototype takes any long runs of 24 volts into consideration. If it were me, I would do as Bob originally suggested and keep it simple, and that would mean switching the 120 volt side of the transformer.

 

[ptonsparky]

One thing I did wonder was if you were trying to use a $40 relay to replace a $3 switch.

One thing to consider when designing 24 volt systems. The voltage drop on 24 volts is going to be 5 times greater than on 120 (given the same load), so switching the 120 volt side makes more sense in a large warehouse. Make sure your prototype takes any long runs of 24 volts into consideration. If it were me, I would do as Bob originally suggested and keep it simple, and that would mean switching the 120 volt side of the transformer.

$28 so that helps a bit.

 

[ActionDave]

It's more about the theory now. Also I have an assortment of relays etc

Have you ever seen a GE RR relay set up. Kwired described them in an earlier post. You can control a light from one to three dozen locations with two wires at each switch.

 

[gar]

170326-1324 EDT

I have several comments on the theory part.

1. A simple two switching points 3 way circuit simply performs the logical function of a two input "exclusive or". Memory of the system state is contained in the mechanical position of the two switches.

I can keep the memory state of the system in a circuit that uses two SPST switches, one at each switch location, with the memory state being in the switches, and uses only two conductors to each switch location. This does not require a latching relay.

What is required is a two input "exclusive or" somewhere else. In other words the "exclusive or" function is divorced from the switches.

2. This can be extended to four switch locations by cascading "exclusive or" circuits.

3. I can have both switch locations on the same two wire pair by encoding the switch positions to different tones.

4. I can build a circuit using just two wires going to many switches. The two wires supply power for electronics at each location. The same two wires carry data to and from each location. Now you can do all sorts of things.

5. However in this application I might want to use a GE RR relay (latching relay). At each switch point, and there can be many on a single two wire pair. There would be a normal GE SPDT center spring return switch with two diodes. You figure out how this works, and what the rest of the circuit is.

.

 

[gar]

170326-1358 EDT

ActionDave:

The usual GE RR system uses three wires to each switch location. But many switches can be put on that same three wire bus to control a single switching point.

I have not seen what kwired wrote so I don't know if he showed a two wire approach with a GE RR.

.

 

[ActionDave]

170326-1358 EDT

ActionDave:

The usual GE RR system uses three wires to each switch location. But many switches can be put on that same three wire bus to control a single switching point.

I have not seen what kwired wrote so I don't know if he showed a two wire approach with a GE RR.

.

You are correct gar, I was mis-remebering about the third wire. I have only seen a few of the systems in use and have only worked on one of them, it's in an old apartment building here, usually just changing out a relay. I am a big fan of the system because I have seen how reliable that one is.

 

[kwired]

170326-1358 EDT

ActionDave:

The usual GE RR system uses three wires to each switch location. But many switches can be put on that same three wire bus to control a single switching point.

I have not seen what kwired wrote so I don't know if he showed a two wire approach with a GE RR.

.

Touchplate, used a relay with two coil wires and two switched contact terminals. Every time you energized the coil the switch contact changed state. It only used momentary contact switches for the control switches, but you could put as many of them as you wanted in parallel to one another and pressing any switch would change the output status of the relay.

Now that I have seen a few more responses and reread the OP again, I guess for what he wants to do he can use standard toggle switches, but needs a double throw relay to be controlled by every switch. Two relays get wired just like a traditional three way switch, but any others in between need to be double pole double throw and wired up like a four way switch. Then you could wire up as many single poles as you like with only two wires to each switch and still get 3 and 4 way type responses, but each switch needs two wires back to the relays, or multiwires between switches - which puts you back at 3 and 4 way switches costing less if you have more then just two wires available.

 

[gar]

1780326-1443 EDT

ActionDave:

I have about 40 RR relays in my home, and more switches. Reliability has been very good, partly because of the power supply design I created. My experience is over a 50 year period.

What is really great about the RR system is the simplicity of multipoint control with very simple wiring and small wires.

Back in the 50s the primary selling approach was on cost reduction. It really did not save money then, and certainly does not today. It should have been sold on its logic capability.

.