How do single-pole wall switches work, and how can they fail? Read on for all the details.
Speaking of misbehaving power toggles, a few weeks back (as I’m writing this in mid-December), the kitchen wall switch that controls power going to our garbage disposal started flaking out. Flipping it to the “on” position sometimes still worked, as had reliably been the case previously, but other times didn’t.
Over only a few days’ time, the percentage of garbage disposal power-on failures increased to near-100%, although I found I could still coax it to fire up if I then pressed down firmly on the center of the switch. Clearly, it was time to visit the local Home Depot and buy-then-install a replacement. And then, because I’d never taken a wall switch apart before, it was teardown education time for me, using the original failed unit as my dissection candidate!
Diagnosing in the dark
As background, our home was originally built in the mid-1980s. We’re the third owners; we’ve never tried to track down the folks who originally built it, and who may or may not still be alive, but the second owner is definitely deceased. So, there’s really nobody we can turn to for answers to any residential electrical, plumbing, or other questions we have; we’re on our own.
Some of the wall switches scattered throughout the house are the traditional “toggle” style:
But many of them are the more modern decorator “rocker” design:
For example, here’s a Leviton Decora (which the company started selling way back in 1973, I learned while researching this piece) dual single-pole switch cluster in one of the bathrooms:
It looks just like the two-switch cluster originally in the kitchen, although you’ll have to take my word on this as I didn’t think to snap a photo until after replacing the misbehaving switch there.
In the cabinet underneath the sink is a dual AC outlet set. The bottom outlet is always “hot” and powers the dishwasher to the left of the sink. The top outlet (the one we particularly care about today) connects to the garbage disposal’s power cord and is controlled by the aforementioned wall switch. I also learned when visiting the circuit breaker box prior to doing the switch swap that the garbage disposal has its own dedicated breaker and electricity feed (which, it turns out, is a recommended and common approach).
A beefier successor
Even prior to removing the wall plate and extracting the failed switch, I had a sneaking suspicion it was a standard ~15A model like the one next to it, which controls the light above the sink. I theorized that this power handling spec shortcoming might explain its eventual failure, so I selected a heavier-duty 20A successor. Here’s the new switch’s packaging, beginning with the front panel (as usual, and as with successive photos, accompanied by a 0.75″/19.1 mm diameter U.S. penny for size comparison purposes). Note the claimed “Light Almond” color, which would seemingly match the two-switch cluster color you saw earlier. Hold that thought:
And here are the remainder of the box sides:
Installation instructions were printed on the inside of the box.
The only slight (and surprising) complication was that (as with the original) while the line and load connections were both still on one side, with ground on the other, the connection sides were swapped versus the original switch. After a bit of colorful language, I managed. Voila:
The remaining original switch on the left, again controlling the above-sink light, is “Light Almond” (or at least something close to that tint). The new one on the right, however, is not “Light Almond” as claimed (and no, I didn’t think to take a full set of photos before installing it, either; this is all I’ve got). And yes, I twitch inside every time I notice the disparity. Eventually, I’ll yank it back out of the wall and return it for a correct-color replacement. But for now, it works, and I’d like to take a break from further colorful language (or worse), so I just grin and bear it.
Analyzing an antique
As for the original, now-malfunctioning right-side switch, on the other hand…plenty of photos of that. Let’s start with some overview shots:
As I’d suspected, this was a conventional 15A-spec’d switch (at first, I’d thought it said 5A but the leading “1” is there, just faintly stamped):
Backside next:
Those two screws originally mounted the switch to the box that surrounded it. The replacement switch came with a brand-new set that I used for re-installation purposes instead:
Another set of marking closeups:
And now for the right side:
I have no clue what the brown goo is that’s deposited at the top, nor do I either want to know what it is or take any responsibility for it. Did I mention that we’re the third owners, and that this switch dated from the original construction 40+ years and two owners ago?
I’m guessing maybe this is what happens when you turn on the garbage disposal with hands still wet and sudsy from hand-washing dishes (or maybe those are food remnants)? Regardless, the goop didn’t seemingly seep down to the switch contacts, so although I originally suspected otherwise, I eventually concluded that it likely ended up not being the failure root cause.
The bottom’s thankfully more pristine:
Those upper and lower metal tabs, it turns out, are our pathway inside. Bend ‘em out:
And the rear black plastic piece pulls away straightaway:
Here’s a basic wall switch functional primer, as I’ve gathered from research on conceptually similar (albeit differing-implementation) Leviton Decora units dissected by others:
along with my own potentially flawed hypothesizing; reader feedback is as always welcomed in the comments!).
The front spring-augmented assembly, with the spring there to hold it in place in one of two possible positions, fits into the grooves of the larger of the two metal pieces in the rear assembly. Line current routes from the screw attached to the larger lower rear-assembly piece and to the front assembly through that same spring-assisted metal-to-metal press-together. And when the switch is in the “on” position, the current then further passes on to the smaller rear-assembly piece, and from there onward to the load via the other attached screw.
Snap, crackle, and pop
However, you’ve undoubtedly already noticed the significant degradation of the contact at the end of the front assembly, which you’ll see more clearly shortly. And if you peer inside the rear assembly, there’s similar degradation at the smaller “load” metal piece’s contact, too:
Let’s take a closer look; the two metal pieces pull right out of the black plastic surroundings:
Now for a couple of closeups of the smaller, degraded-contact piece (yes, that’s a piece of single-sided transparent adhesive tape holding the penny upright and in place!):
Zap
Next, let’s look at what it originally mated with when the toggle was in the “on” position:
Jeepers:
Another black plastic plate also thankfully detached absent any drama:
And where did all the scorched metal that got burned off both contacts end up? Coating the remainder of the assembly, that’s where, most of it toward the bottom (gravity, don’cha know):
Including all over the back of the switch plate itself, along with the surrounding frame:
Our garbage disposal is a 3/4 HP InSinkErator Badger 5XP, with a specified current draw of 9.5A. Note, however, that this is also documented as an “average load” rating; the surge current on motor turn-on, for example, is likely much higher, as well as not managed by any start capacitors inside the appliance, which would be first-time charging up in parallel in such a scenario (in contrast, by the way, the dishwasher next to it, a Kenmore 66513409N410, specs 8.1A of “total current”, again presumably average, and 1.2A of which is pulled by the motor). So, given that this was only a 15A switch, I’m surprised it lasted as long as it did. Agree or disagree, readers? Share your thoughts on this and anything else that caught your attention in the comments!
—Brian Dipert is the Principal at Sierra Media and a former technical editor at EDN Magazine, where he still regularly contributes as a freelancer.
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