Three Way Switch Connundrum


  #1  
Old 01-23-14, 01:10 PM
S
Member
Thread Starter
Join Date: Sep 2008
Location: Canada
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
Three Way Switch Connundrum

I want to replace a three way switch with a Z-Wave switch and corresponding transmitter. I am happy with how to get everything wired up once I have definitively validated how the current three way switches are wired which brings me to my current issue:

I shut off the power to the circuit associated with the three way switches (driving incandecent lights). Without disconnecting any wires on one of the switches I checked for continuity between the hot wire screw terminal on the switch and the each of the traveller terminals. There was continuity between the hot terminal and only one of the traveller terminals.

I then flipped the position of the switch and rechecked for continuity and in this other position (I recall that one swith was "ON" and the other was "OFF"), I had continuity between all three terminals on the switch (i.e. Hot to Traveller 1, Hot to Traveller 2 and, I believe, between Traveller 1 and 2).

As noted, all wires were still connected and the breaker was turned off but for the life of me and after diagramming the switches, I cannot figure out where there would be continuity across all positions when the switch I was testing was in the opposite state as the other switch. Operationally, there is no problem with the switch as it works as you would expect a three way switch to work.

Am I missing something here?

Thank you!
 
  #2  
Old 01-23-14, 02:45 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 29,711
Upvotes: 0
Received 15 Upvotes on 13 Posts
There was continuity between the hot terminal and only one of the traveler terminals.
That is normal. Only one traveler will show continuity to the common. Which traveler depends on the position of the switch. See illustration below:

Name:  3-way-1_zps20adb6a8.jpg
Views: 319
Size:  9.9 KB

(I recall that one switch was "ON" and the other was "OFF"
As you can see from the switch above there is really no off position. Off occurs when the traveler of the common connected to the light is not the traveler connected to the common that power comes in on.

 

Last edited by ray2047; 01-23-14 at 04:40 PM.
  #3  
Old 01-23-14, 08:19 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 64,588
Received 3,880 Upvotes on 3,477 Posts
I like that Ray

When you use a meter to measure the continuity in a circuit, like you are doing with your 3 way lighting circuit, you have to take all loads on that circuit into consideration.

You are measuring resistance between the common or hot wire and your travelers. If you notice in my illustration I drew in "other loads." These would be other things on the same circuit. They could be anything... TV, lights, radio, etc.and since they are connected to the same circuit as your 3 way, they will also throw off your resistance measurements. These loads are one reason why you can measure continuity between both travelers and the common.

Name:  ll.jpg
Views: 568
Size:  14.4 KB
 
  #4  
Old 01-24-14, 01:07 PM
S
Member
Thread Starter
Join Date: Sep 2008
Location: Canada
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
PJMax - I believe that is exactly the issue (other loads on the circuit) as to why I was able to measure continuity between the hot and both traveller terminals.

I am going to print off your diagram and spend a time of time working through it. Thank you!
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: