Relay for 3 way switching with 2 wires

[justin13me]

Other than a latching relay (with momentary pushbutton switches in parallel) can you use a (solid state/ mechanically held) NO and NC relay with 2 single pole toggle switches to make 2 3ways?

For example let's say there's a switch in a wall w 2 conductors and wireless not being an option, you'd like to turn it into a 3way with a non latching contactor/ relay. Theoretically worked out in my head but not in test application pictured.

Thanks!

 

[ActionDave]

Without a latching relay you can't.

 

[gar]

170326-0849 EDT

justin13me:

Your question is not sufficiently well defined.

Your limitations are not clear.

If you do not use the combinatorial switch logic or similar logic to an ordinary 3-way, then you need some sort of memory device in your system.

How many allowed wires between what points? Can power to the load be supplied from other than these wires? What restriction on memory devices? You have indicated a latching relay is not allowed. What is the definition of a latching relay? Is a flip-flop a latching relay? Is data stored in a memory a latching relay?

.

 

[justin13me]

2 LV wires to each switch and a relay w NO, NC & Common in between. Whether the same cct for all or LV controlling a high voltage, I don't think it works. Maybe 2 (of these) relays..? Anyways, I've decided to run a new 3 wire end to end across a big warehouse as cost wise it works out the same or less depending on the type of latching power pack, momentary pushbuttons etc. Also there's a scissor lift on site.. Still curious though, as it may be possible (?) but beyond my expertise level

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[iwire]

With only two conductors and a basic relay you cannot control both ON and OFF functions from more than one location.

 

[justin13me]

With only two conductors and a basic relay you cannot control both ON and OFF functions from more than one location.

Thanks. I've come to the same conclusion: w 1 relay, at best you get a 3 way in series /wrongly wired 3 way result: sometimes works & sometimes not, if you start mixing up turning on/off locations.

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[iwire]

Your question is not sufficiently well defined.

It is pretty clear to me and I bet other electricians as well as this is the kind of problem that comes up all the time.

He has only two available conductors run to a distant point, he would like to use those two conductors at that distant point to install a switch to control something that I assume is lights. This is in addition to at least one other switch location.

Using just the basic and readily available methods the OP has suggested will not do it.

Of course we could get into a ton of ways to make it work with just two conductors but in my experience it is often easier, quicker and more reliable to just bite the bullet and pull some more conductors.

No reason to use a sledge hammer to put in a carpet tack.

 

[iwire]

Thanks. I've come to the same conclusion: w 1 relay, at best you get a 3 way in series /wrongly wired 3 way result: sometimes works & sometimes not, if you start mixing up turning on/off locations.

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Think of it this way.

Can you wire standard three ways with just two conductors?

Changing the switching device from a 3 way switch to a relay does not change that.

 

[peter d]

Of course we could get into a ton of ways to make it work with just two conductors but in my experience it is often easier, quicker and more reliable to just bite the bullet and pull some more conductors.

No reason to use a sledge hammer to put in a carpet tack.

:thumbsup:

I always try to avoid unnecessary complexity. I especially try to avoid things that will be prone to failure down the road, like contactors and relays, if at all possible.

 

[iwire]

I have not put a ton of thought into this but if I was stuck with two wires I might go with a normally open push button combined with an alternating relay and a contactor.

But like Peter said, do not make it complicated to repair if you do not have to. At some point down the line what we do will likely need troubleshooting and if you make it odd it only cost the customer more later.

 

[ptonsparky]

I agree.

As much as I try to accommodate a customers wishes via available technology sometimes they would be better off with just a dang switch and change of attitude.

Sure is fun to over complicate things and see it work though.

 

[K8MHZ]

Can't get a cable from one switch to the other?

 

[iwire]

Can't get a cable from one switch to the other?

They can, they just wanted to avoid it if they could.

Anyways, I've decided to run a new 3 wire end to end across a big warehouse as cost wise it works out the same or less depending on the type of latching power pack, momentary pushbuttons etc. Also there's a scissor lift on site..

For instance for us if there was no lift on site that would add about $500 to the cost of running the wire.

 

[K8MHZ]

They can, they just wanted to avoid it if they could.

Let's say the OP's setup could be configured to work. Somehow, there still has to be some sort of wire, even if it's to control a relay, from the new switch location to either the old switch location or the light, correct?

 

[iwire]

Let's say the OP's setup could be configured to work. Somehow, there still has to be some sort of wire, even if it's to control a relay, from the new switch location to either the old switch location or the light, correct?

Maybe go back and read the thread.

 

[K8MHZ]

Maybe go back and read the thread.

I have, and I still have the same question.

The OP said no wireless, thus, all devices have to have some sort of wire connection to each other, do they not?

 

[K8MHZ]

I think the OP is trying to solve a problem that doesn't exist, that's why I am asking about the proposed wiring paths of the desired relay controlled configuration.

 

[iwire]

I have, and I still have the same question.

He has two existing conductors he was trying to use, it wont work, he decided to pull a new three conductor cable.

 

[K8MHZ]

​

He has two existing conductors he was trying to use, it wont work, he decided to pull a new three conductor cable.

You may have to 'splain this to me.

Right now, he has one switch with two conductors going to a light, correct? He wants to add another switch to operate as a three way, correct? For some reason, he wants to use a relay. That relay has to be located somewhere and connected to the switches somehow. Is there already two switch locations with only two wires connecting them, or is a new switch location going to be added?

Edit to add: Is he pulling a new three conductor cable from the existing switch to the light?

 

[justin13me]

You may have to 'splain this to me.

Right now, he has one switch with two conductors going to a light, correct? He wants to add another switch to operate as a three way, correct? For some reason, he wants to use a relay. That relay has to be located somewhere and connected to the switches somehow. Is there already two switch locations with only two wires connecting them, or is a new switch location going to be added?

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!