How can I combine two switches on two circuits on 1 timer switch?

Question

I just purchased my first house (new construction) and I got tired of remembering to switch the outdoor lights on/off every day. So, I got a Honeywell solar econoswitch, which is essentially a timer switch that knows when the sun goes up and down through long/lat.

There are 5 lights total outside, 2 connected to one normal switch and 3 connected to a 3-way switch. Each switch is on a different circuit. I have already successfully connected the econoswitch to the 2 lights on the normal switch. But ideally want all 5 lights connected to this econoswitch. I'm a new comer to DIY electricity so I'm a little nervous and want to make sure I do it right. I drew a diagram how it's connected right now-

The parts that i'm not sure on are:

1.There are two neutral lines on different circuits. Do I connect them together if I combine the switches?

2.How do I connect the three way switch? I understand I'll probably lose functionality on the other switch the 3-way is connected to and that's fine but I want to know best way to do this.

Answer 1

Since you have two circuits (i.e. two home runs from the electrical panel) in play here, you can't "combine" the switches in the manner you're thinking of. This leaves you with two options:

1. You can buy a second RPLS540A EconoSwitch and install it in place of one of the 3-way switches for the outdoor lights as per the instructions. This is the simplest approach, but leaves you with two EconoSwitches to program and the possibility that your two sets of lights will wind up "out of sync".

2. If you have a neutral in the box for the single pole EconoSwitch, this also raises the possibility of a setup using a SPDT relay in place of one of the three-way switches with its coil controlled by the existing EconoSwitch; this would require running an extra cable from the box with the single pole switch to the box with the three-way switch for the outdoor lights, though. You would also need to swap the existing EconoSwitch for a RPLS740B: the RPLS540A you have passes the power it uses to operate through the load, while the RPLS740B uses a neutral wire of its own to get its operating electricity "back home", so to speak.