Unfamiliar Existing Switch Wiring - Neutral Wire for Smart Switch Help Needed!

Question

I recently become a home owner and have been looking forward to start working on making it “smart”, however, it seems like I’ve ran into a blocker just as I was getting started.

I’m replacing standard “dumb switches” and got off to a good start with my first attempt. Pretty simple, black, red, white and ground all wired to the smart switch (Kasa Smart Light Switch HS200P3).

Upon starting to swap out the next switch, I found it odd that although there were “ground” wires in the box, none of them were actually connected to the dumb switch. I figured it might have been an oversight. I removed a handful of other switches throughout the house and came across the same scenario.

The ground wires would typically be ~4 for a 3 switch hookup but they were all twisted together. I did find another ~4 white, neutral, cables bundles together & thought okay - maybe they were lasy to get the ground wires but at least I have the neutral wires to use for my smart switch and the ground wires to get those connected.

I got load, line, neutral and ground hooked up to the smart switch. The smart switch does show signs of power as it lights up a wifi symbol, however, the switch when on/off simply don’t result in the lights powering on or off.

I disconnected neutral and reconnected dumb switch back to line, load, & now ground - works just as it was. Figured I might have missed something when wiring the smart switch so got it rewired - same behavior.

I’m not sure if it’s a neutral wire that may be causing the issue or anything else I may be doing wrong. I’ve wired various of the switches at my previous residence and it was a breeze…

I thought I might have a defective smart switch so tried another one - same issue.

I’m new to the home improvement community but eager to learn more even if it requires trial and error but I’m stuck on what I should check for next, attempt to determine root cause, or if there’s something I’m simply doing incorrectly.

Any feedback, whether criticizing my lack of knowledge or providing resources/tips on how to get this working would be greatly appreciated!

Answer 1

The good news is that it sounds like you do have neutral in your switch boxes. Note that switches in old houses can use white for hot instead of neutral. But current code requires neutral in most switch boxes because many smart switches, timers, motion sensors, etc. have neutral. So taking the wires step-by-step:

• Ground - green or bare

This is the easiest one, so I'll take care of it first. Many dumb switches either don't require ground or, if they are in metal boxes, ground through the yoke. As a result, you can legitimately find ground wires in a switch box but not connected to the switch. If a new switch requires ground and doesn't ground through the yoke (either because it is not designed to do so, or because you are not using a metal box), connect a ground pigtail (a short piece of appropriately sized green or bare wire) from the bundle of grounds to the switch ground screw.

• Hot - Usually black or red

It is important to figure out which wire is hot. By convention this will usually be the black wire. But it does not have to be! It can be red. It can, if wires are in conduit instead of a cable, be blue or yellow or some other color (except white, gray, green or bare). The key is that with a dumb switch there is no difference between hot and switched hot - they can flip places and the switch will still function 100% correctly. But with a smart switch (or timer or motion detector etc.) you must figure out which wire is hot and connect it correctly. If you are not sure, the way to figure this out is:

• Turn off the breaker

• Disconnect the hot and switched hot wires and cap them with wire nuts for safety and make sure they are a few inches apart

• Turn on the breaker

• Use a non-contact tester to see which wire is hot

• Switched hot - usually red or black

Same deal as hot. Usually red. Sometimes black. Other colors (except white, gray, green or bare) OK if in conduit. Figure out which wire is hot. The other one is switched hot.

• Neutral - usually white

Neutral must be white or gray. In a cable it will always be white. Older houses don't require neutral in the switch box, which often resulted in switch loops that function just fine except that they don't provide a neutral for smart switches, etc. You mentioned bundles of neutrals, so you should be fine. Add a white pigtail to the neutral bundle and connect it to the appropriate screw on the new switch.

Based on the description, the most obvious problem is hot/switched hot reversed. But there could be other problems. If carefully working through the wires doesn't resolve the problem, provide more details (and pictures) and we'll try to help.