3 way switch

5 Posts
Oct 16, 2006 02:07 pm
3 way switch

I have a 3 way light for my stairs. The power comes in at the switch. The light is in-between the 2 switches. I have followed the illustrations/instructions from a Handyman how-to book that gives instruction in AC wiring. My problem is only one side of the system works.If one of the switches is in the on position both switches work but if that one switch is in the off position no switch works. Can you give a helping hand with setting up these switches for DC ?
 
30 Posts
Oct 16, 2006 04:31 pm
Re: 3 way switch

Hi Bruce - it doesn't matter if the power is AC or DC, the wiring of a 3-way circuit is the same.  I'm guessing you've checked and double checked your wiring to the diagram you are using (I don't know, but perhaps the book has it wrong). If you post an email address I can send you a wiring diagram to try.  I would caution you that using inexpensive, readily available 3-way switches commonly used in the AC world could be a problem. They typically aren't rated for DC use. To be safe, I would recommend using a commercial grade switch and limit (by limiting the number of lamps and their current rating) the switching to a couple of amps.  The problem is that arcing in switches (happens in all of them), particularly when breaking contact, is typically quenched as the voltage passes through zero (in the AC cycle).  In a DC circuit, this doesn't happen.  Generally this means that the life of the switch will be shortened vs. AC use.  In extreme cases, it could be a fire hazard.  So limit the DC current you are trying to switch to well below the rating of the switch.  Anyway, let me know if I can help you with your wiring circuit problem.

Regards -

Tom Hardy, PE
HVTA, Inc.
 
5 Posts
Oct 16, 2006 05:07 pm
Re: 3 way switch

Thanks for the reply Thomas. I am using DC rated switches and suppose one of them may be bad. I have blown enough fuses configuring different ways to connect 2 3 ways and 1 light. I would appreciate your diagram. About the DC switches. I am going thru a person that deals from this site and tells me most folks are using AC switches cuz they are more available  and cheaper. Says AC will work but with a shortened life. Are DC swathes still being made ? E-mail basmith @ cablemt.net
 
578 Posts
Oct 16, 2006 07:35 pm
Re: 3 way switch

dc switches are getting very hard to find.  I think we still carry one that I went out of my way to source for a cabin guy.  That one was only a two way switch.  let me know if you need one, or if you think we should have it on the website.

oh yeah, T rated switches will also work to the best of my knowledge.  the one we carry is  a surface mounted T switch, and it is ugly and brown, but safe for 12v dc situations. 

If I could avoid it, I would not use an ac switch for dc loads. 

Also, good ole square d "QO" circuit breakers are dual rated for dc usage up to 48 volts total.  for battery apps 12 or 24vdc is okay, for solar, we stick to 12vdc nominal only because of the possibility of going over the 48v rating.

- james Alt-E staff

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Fax: 877.242.6718  or +1.978.562.5854
« Last Edit: Sep 26, 2008 12:54 pm by James Cormican »
 
5 Posts
Oct 17, 2006 09:42 am
Re: 3 way switch

Thanks for the reply James. Don't know if the site needs the switch but if it did I would buy 4 Ea. single switches. I am setting up a 24vdc system. All my lights are DC. About 12 lights on 5 diff. circuts with the Edison base adaptor for the Halogen 2 prong 50w.bulb inside and 20w outside. With what is not working with my 3 way I will assume one of them is bad and use an AC switch to check before I need to order a 3 way.Electricity sucks when all I know is new batteries make my Flashlight work.
 
351 Posts
Oct 17, 2006 01:59 pm
Re: 3 way switch

Bruce:

I don't think its the switch. It sounds to me like you are cross wired, most probably in the light box. But check the wiring at both switches and the light.

Your switch that always works should be the one where the power source is. The power enters this switch box with 2 wires which I will call black (hot) and white (Neutral). The black should connect to the pole near the bottom of the switch. You need three wires from this point. The red and black (Both will be Hot)should be connected to the 2 upper poles. Connect the two white wires with a wire nut.

In the light box, both the the red and black wires should be connected to the red and black that run to the switch at the far end. Connect the white wire (From the first switch box) to the white wire off of the light. Take the white wire that is going to the switch at the far end and wrap some black tape around the insulation (Or use an indelible black marker) as a "Hot" id. This w/b wire is the hot return from the far end switch, connect it to the black wire of the lamp. (from this light box to the far end switch, there is no neutral. all three wires are considered hot.)

At the far end switch The red and black should be on the upper two poles of the switch. The white wire should also be marked with black tape or ink and this wire should connect to the bottom pole of the switch.

Hope that helps.

Ken

 
Oct 29, 2006 02:22 pm
Re: 3 way switch

It sounds as though you might have a "traveler" wire mixed up with a line or load wire. 
One way is - positive and negative would enter one switch box. The pos. (line) would terminate on that switches common screw. Two travelers would terminate, one each on the other two screws. The travelers along with the neg. would then go to the light box. This is where the neg. would terminate on the screw for the outer threaded ring of the lamp holder. The two travelers would then continue to the next switch box and terminate the same as before. Then pos. (load) would come off of that switches common screw and go back to the light box and terminate on the screw for the center pin of the lamp holder.

Even though the wires may be run differently from house to house the principle is the same. For example; pos. and neg. may enter at the light box but there only needs to be three conductors going to each switch box. Two travelers and line to one switch, two travelers and load to the other switch.
 
With the circuit dead and all wires separated at each box use a meter that can "ring out" continuity and identify each wire at each box with colored tape. Make pos. red and neg. black. Make one traveler blue and the other orange. Once everything is identified I think it will be an easier task for you to figure it all out. Easier said than done I know. (One of my money making skills is troubleshooting industrial motor control wiring at places like, but not limited to cotton gins.) You will need a Length of wire and maybe some help to accomplish this. If the common screws on the switches are not identified by the manufacturer you can use that same meter to find out which is common because only one screw will "ring out" to the other two depending on how the toggle is positioned.

On a side note - what clarified 3-way, 4-way switching for me was hearing the words, "you can have as many 4-ways as you want as long as there is a 3-way at each end."

 Knowing your travelers from line from load is the key.
 
Oct 29, 2006 02:29 pm
Re: 3 way switch

Something I neglected to tell you was that sometimes positive and negative are "Daisy chained" form one box to another box continuing a branch circuit that is supplying power for other needs throughout the house.
 

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