We have a light switch box containing three single pole switches (no ground terminal) in the foyer near the front door. I would like to replace the light switch controlling the porch lights with the Honeywell Programmable Timer Switch RPLS740B. Given the following conditions, I could not determine any wiring combination such that all related electrical components worked.

Here is a picture of the actual timer followed by its simple wiring diagram: Programmable Timer Wiring Diagram

The light switch box consists of a switch that controls nothing, a switch that controls the chandelier in the foyer, and a switch that controls the front porch lights (in that order). Note that the first switch affects no known electrical appliance without a doubt. Whether this is due to improper or faulty wiring I'm not sure. Also, this is all the original wiring (as built).

Light Switches

The light switch box also consists of 1 "three-wire" cable (red, black, white, copper) and 5 "two-wire" (black, white, copper) cables. Note that these are also termed "four-wire" and "three-wire" respectively.

Exposed Light Switches

The original wiring setup seems rather simple in that all ground wires are tied together, all black wires are tied together, and all white wires are tied together. Each of the switches is connected to the single black wire belonging to the "two-wire" cable at the bottom of the box, which I assume to be the "line". However, since all the black wires are tied together, this appears to be inconsequential.

Exposed Light Switches Side Wiring Exposed

Simply replacing the porch light switch with the timer as expected does not work at all. Freeing particular white "neutral" wires does cause the timer to function but would also cause various fans/lights in the adjacent study to stop functioning. Is it common for a light switch box to have so many incoming cables? Why does the first switch even need a red wire if its a single pole switch?

[Resolution Edit]

I mistakenly assumed that the line was located at the bottom of the switch box when in fact it was the first cable at the top. With this knowledge I was able to determine the unknown loads as seen below (for future reference).
enter image description here

et voilà enter image description here

  • How many lights were controlled by these switches? Now that it's all ripped apart, what doesn't work (receptacles, lights, etc.)? Which switch were you trying to replace? Why did you decide to rip everything out of the box? – Tester101 Mar 24 '15 at 21:52
  • @Tester101 The middle switch controls the chandelier, the last switch controls the front porch lights. Everything is back together and everything works as before. I decided to rip things out for pedagogical purposes and to ensure clarity. – metabind Mar 24 '15 at 22:58
  • so you got the timer installed, or just back to square one? – Tester101 Mar 24 '15 at 23:03
  • @Tester101 I'm back to square one. Also, I added more info to the post that may be useful. – metabind Mar 24 '15 at 23:05
  • Where did you get acquire the cover plate? I have a similar set up with three on/off toggles but only want to replace one to control my outdoor accent lighting. I have not been able to find anything online. – brent Nov 15 '16 at 15:42
up vote 1 down vote accepted

Based on what you've shown, you should be able to wire it up like this...

Timer Wiring

However, those red Wing-Nut® twist-on wire connectors are only rated for a maximum of 6 #14 conductors. So you'll have to split up the neutrals in to two groups, and connect the groups with a pigtail between them.

  • My first attempt was precisely as you have it shown, which does not work. I suppose the error could be related to the wing-nut restriction, but that seems unlikely. Also, I was able to get it to function, but only by disconnecting the unused cables as mentioned above. – metabind Mar 25 '15 at 0:08
  • If that doesn't work, there's something funky going on that we don't know about. Could be a bad device, bad wiring, or something else. Without being able to poke around and put a meter on stuff, it's difficult to go further through the internet. – Tester101 Mar 25 '15 at 0:22
  • I will say that the white wire with the black marker on it has me slightly concerned, as that's typically done when a white conductor is used as an ungrounded conductor instead of a grounded one. It also appears that the marked wire is from the 3 wire cable, that is attached to the switch you say does nothing. – Tester101 Mar 25 '15 at 0:33
  • Did wiring it this way work? – Tester101 Mar 25 '15 at 21:22
  • Your suggestion of splitting the neutrals (and the lines) into two groups with a pigtail was also required. – metabind Mar 25 '15 at 22:27

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