Halloween Horror: Line Voltage on the Loose!

I hauled the Kenmore 158 sewing machine and controller to a Squidwrench meeting for some current measurements (and, admittedly, showing it off) while schmoozing. After hauling it home and setting it up on my bench again, it didn’t work: the motor didn’t run at all.

While doing the usual poking around under the cover, I spotted this horrifying sight:

Loose AC line hot wire
Loose AC line hot wire

The brown insulation tells you that’s a hot wire from the AC line and, in fact, it’s coming directly from the line fuse; it’s live whenever the plug is in.

It’s a stranded wire to allow flexing without breaking, but that same flexibility allows it to squeeze its way out of a tightly fastened screw terminal. In principle, one should crimp a pin on the wire, but the only pins in my heap don’t quite fit along the screw terminal block.

This sort of thing is why I’m being rather relentless about building a grounded, steel-lined box with all the pieces firmly mounted on plastic sheets and all the loose ends tucked in. If that wire had gone much further to the side or top, it would have blown the fuse when it tapped the steel frame. The non-isolated components on that board are facing you, with those connections as far from the terminal block as they can be.

Engineers tend to be difficult to live with, because we have certain fixed ways of doing things that are not amenable to debate. There’s probably a genetic trait involved, but we also realize that being sloppy can kill you rather quickly; the universe is not all about pink unicorns and rainbows.

In fact, the universe wants you dead.

Now, go play with those goblins and zombies tonight…

Memo to Self: Tighten those terminals every now and again. A wire will come loose shortly after you forget to do that, of course.