ECN Forum Forums General Topics of the Trade General Discussion Area Kiln Killin' (Near-miss)

A General Contractor's wife inherited her grandmother's pottery kiln. I was called in to provide a feeder for it, and replace the cord.

125/250V 50A originally, 3-wire, no ground.

Nameplate says 36A, so 50A it is...

The old three-wire cord looked bad, burnt from loose receptacles, or similar...

I decided to replace the cord, which was a range-type cord, with a four-wire, since I was providing the receptacle too.

I checked for neutral to chassis continuity on the kiln, but there was none. Parallel neutral paths were not a concern. While removing the old cord, I found under the brittle black electrical tape uncrimped crimp-type lugs, with a very small dab of (cold) solder on the tip to, uh, "hold" the wires in... sheesh!

I used split bolts with a layer of varnished cambric and Scotch 130C. I drilled into a conveniently thick part of the chassis, and tapped it out to 10-32, and scraped the paint off for the EG screw.

Closed the cover and fired the baby up... one switch OK, two switch, OK three switch BAM!

OK... turn circuit off, unplug Kiln, remove cover.. no sign of damage... OK, remove panel cover for rotary switches, and Aha!

Apparently at one time, a switch became a problem, or maybe a pilot light, when the switch panel cover was replaced, a terminal was bent backwards and made contact with the chassis. Dead short.

So, the chassis had been becoming hot when the lower element was used. Luck was the only thing protecting her grandmother.

The current owner has the kiln in her garage on a concrete floor, and potters like to go barefoot. You must touch the frame (the safety switch has to be held on, it's metal) when the rotary switches are moved.

Plus, the husband told me that she's very sensitive to electricity...

I think it was $100 well spent...

Grandmother must have always worn shoes.
Fortunately you got there before a plumber hooked it up for them. Another good save!

electure,

What does a plumber hook up on a kiln?
(or was that a joke?)

Bill

Nothin' like a little fault current to make an impression eh?
To this day, I turn breaker, switches,etc on @ arms length, finding a solid hand placement first, and looking away before activating......

I think I'm going to start that habit...

>What does a plumber hook up on a kiln?
Yeah, it was a joke - or a slight.
It's an inside joke among us all now, is it not?

Plumber's light pole was a recent installment.

Is this a timed-bake machine? What are the neutral loads?

OK,

I'm on track now!

Bill

Dspark,

Two upper elements were on one 120V leg, each with its own switch, the lower element was on the other leg. The rotary switches had "HI" "MED" "LO" and "OFF" positions. It ws really a multiwire setup rather than a true 125/250V.

There was a gravity type thermal cut-off safety switch that had to be held into place to turn the unit on, and a thermal coupling to a temp guage with a switch to choose upper or lower probes.

No timer, very lo-tech. (read old)

Other than the obvious problems, it seemed in very good shape.

The conductors were insulated with a waxy paper looking fiber, very easy to strip, but in good condition. The only things in bad shape were the work of various "handymen" through the ages.