So just how hard is it to pull new wiring into a typical switch loop?

Question

I'd like to install more home automation. Unfortunately at least half my house is wired with old switch loops which have no neutral in the box. I also have ceiling fans with lights on switch-looped circuits with only one controlled hot; there are smart controls I can install into the fan housings but that's arguably a bit inelegant.

The wiring runs through an under-the-roif space that isn't even crawlable, so hand-dropping 14/3 NMC isn't a real option unless I rip open ceilings.

I'm not sure whether these are all conduit (with at least one bend between fixture and switch), NMC (ditto), or a mix.

I'm perhaps unreasonably paranoid that friction in the bends, or a staple holding NMC if that's what I'm dealing with, will make just using existing wires to pull new wires impractical, and that I'll wind up having to do surgery to recover.

Given those two possibilities; How Hard Would It Probably Be in either case to upgrade this wiring to three conductors (so I have neutral in the switch box) or four (so I have hot, two switched hots, and neutral)? Any way to make it easier?

(I know any given building may have done something unreasonable; my question is whether it's worth trying in the hope that past electricians were competent, or whether putting smarts I to the fixture really is my best bet.)

Answer 1

If you have conduit, relatively easy. But I doubt you have conduit, just statistically speaking, since you are not in Chicago or New York City. Easy enough to tell - just open a box and look at the wires. If they are clamped with a bit of sheath showing, they are cables. If they are loose coming through a pipe of some sort, they are wires in conduit.

The problem is that NM cable must be secured when installed in open walls. Since installing in open walls, and then closing the walls, is the normal building method in the US for the past 100 years, you almost certainly have staples on every cable on every stud. The exception is if the cables are added after initial construction - then you have loose cables inside walls and some (small) hope of being able to use the old to pull the new. But realistically if you want to add new cables you abandon the old cables in place.

For most homes, the options are routing cables from underneath, if you have an open basement or an accessible crawlspace, or from above, if you have an attic. Or maybe some of each. All of which can be a real pain to do.

The alternative is smart switches that don't require a neutral. Smart switches (and motion sensors and electronic timers, etc.) need power and they can get it one of a few different ways:

• Batteries - Not great, particularly with WiFi or other relatively large power needs. But can work for some situations, such as "remote" switches using low-power (not WiFi) to communicate with the master switches.
• Leak current through the load - works great with incandescent, not so great with LED or non-lighting loads.
• Neutral - as you know, this is the best way to do things but often not practical due to wiring issues
• Ground instead of neutral - this is a workable solution but only when designed appropriately and approved by UL, ETL or a similar NRTL.

Not the answer you want to hear. But the reality is that adding new cables is not always an easy task. In my house, except for kitchen renovation (walls open, panel directly underneath, so no problem) I've (my electrician really...) only run 3 new cables. Two were for bathroom heat/fan/light, done by working in the attic, which was necessary to connect the exhaust ductwork anyway. The other was for a ceiling light - up from the bathroom lighting circuit, into the attic, externally across the peak of the ceiling (which I immediately covered with molding - looks like it was built that way) and into the ceiling and down to the light fixture location. Only had to patch one chunk of drywall, so not too bad. But still not a simple task.