John Rodgers on sun 19 oct 08
This discussion about the above subject is one everyone should get a
grip on. Not having this right could cost a load of pottery, a kiln,
your studio, your house, your life.
I was going to write a lengthy essay about this - BUT - I found the link
below and I can't even come close to what is presented in such a
coherent way. Since this subject of electrical power is so important to
us as citizens, and particularly as potters using electric kilns and
other related equipment, I would like to encourage every one of us to
read this article on the internet. We DO NOT need to take the issue of
electrical power lightly. We need understanding to protect ourselves.
So please read the entire article at the link below. It will explain
much and it worth knowing.
http://science.howstuffworks.com/power2.htm
One comment. Electrical power is supplied to your house via three wires
- two "legs" of 120 volts each, and a neural or ground. The house
service panel is usually limited to 200 amps. There should be a 200 amp
breaker on the panel somewhere. When all else fails, you can trip that
breaker and turn the power off to the entire house. When the power is
attached to your breaker panel one side of the panel gets one leg, the
other side gets the other "leg", the neutral grounds the whole thing.
When the electrician installs your kiln outlet for which to power your
kiln, he connects one hot "leg" to one pin in the receptacle, and a
second hot "leg" to the other pin in the receptacle. He connects the
neural or ground to the third pin. So you have two sides of the box -
120V on each side, each connected to a common ground, and totaling 240V.
The engineers, in designing your kiln, took into consideration all the
operating parameters of the materials in the kiln, and they marked the
current demand for all that somewhere on the kiln - usually on the data
plate along side the voltage. If a circuit breaker is installed that is
properly mated to the kiln, then any short in the kiln or anything else
which tends to draw more current than that of the design parameters,
will cause the circuit to heat to the point the circuit breaker trips
and shuts off the power. If the circuit breaker is over- rated, or rated
two high, the shorted kiln will just pull more and more amps, and
components will get hotter and hotter, until something catches fire or
melts. Very bad news. And ironically the fire may not be in or around
the kiln - it may be inside the house in a wall somewhere, thus setting
the house on fire.
So, fellow Clayfolk, getting this electrical business down pat, and
having a good understanding of it, is as crucial if not more so, than
having and understanding of how to work clay with your hands. It could
mean your life.
Now a story -
I had a kiln I wired up, and I had to jury-rig a connection set-up
because of where I was located, and to get from the breaker panel to the
kiln, I had to make up a big hairy extension cord that would carry the
voltage and the amperage. When I would fire, I would un-roll this power
cord, plug the kiln plug in to the receptacle box on one end, and then
the other end to the cord into a receptacle mounted directly to the
circuit breaker panel box. Now granted this is not the best nor safest
was to do things, but I was disparate to do clay, right? Well, add to
that the fact that the three wire cable I was using was one designed to
be buried under ground, where temperatures would remain constant. Plus,
it was a cable I had salvaged from going to the scrap yard when some
construction work was being done. Well, everything was working great. I
was throwing and firing pots of my jury-rigged set-up and threw and
fired pots all spring. Daily I would un-roll my power cord and lay it
out on the sidewalk over to the power panel to plug it in. I was pleased
with myself. The days passed, and the days got longer and hotter. And
then one day, right in the middle fo a firing, I heard the breaker trip.
At first, I sat right upright "What was that?" I was almost afraid to
ask myself. I went to the breaker box - the breaker was tripped. Hmmmm!
I thought. I reset the breaker, a few minutes later, the breaker tripped
again. Drat - beaker is worn and won't hold ( that does happen). I
disconnected the kiln, popped open the box, pulled the breaker, and
raced to the electrical supply house. bought another breaker - paid the
man his $50 bucks, and sped back to the breaker panel. Installed the
breaker in record time, Plugged in the kiln and continued the firing. It
worked great. It was afternoon, beginning to cool off, my workspace was
not in the sun - and the kiln was firing. Two days later, I got ready
to fire another load. I started early. Sun was approaching zenith over
my shed when I put the last piece in the kiln, and turned on the power.
I went to work on throwing more pots, and the kiln just hummed right
along. At about 3 hours into the firing the kiln was pulling full power,
and "CLICK" I hear that brand new breaker trip. I ran out in the sun
and re-set the breaker. In just a few minutes - "CLICK!". breaker
tripped again. Three times I tried. Then for some reason, I reached down
and grabbed the power cable. That sucker was hot!! I was really puzzled.
Why would the power cable be hot. Everything had been working. I even
had a new breaker. I stood there, sweating in the summer heat. The light
dawned!! The cable I was using was a number 6 underground cable -
adequate for cool stable temperatures. But lay that cable in the sun and
get it hot - and the resistance in the cable goes way up - increasing
current draw. And combined with that of the kiln it was enough to trip
the kiln breaker every time during the hottest part of the day. I went
and got me a number four cable which lowered the resistance and it has
worked ever since. I still use that cable on occasion. When I need to
run two kilns at once I just plug that cable into a special receptacle
on my power pole and have at it. Works great. There are hazards though.
Like the time my neighbor got drunk, and in a fit of generosity when I
was having severe sciatica and could not cut my own grass, he took it
upon himself - without even asking - and in the middle of an absolute
downpour of rain, right at dark when not one soul see squat, he decides
to cut my grass with his riding lawn mover and runs right over my power
cable and cuts it in half - $350 worth of number 4 rubber cased outdoor
insulated copper wire. It was a wonder it didn't kill him. But
fortunately it was my habit to pull the plug a the pole end when there
was no firing taking place. So he survived, fortunately. He was very
chagrined the next day. .
John Rodgers
Chelsea, AL
KATHI LESUEUR on mon 20 oct 08
On Oct 19, 2008, at 8:46 PM, John Rodgers wrote:
> This discussion about the above subject is one everyone should get a
> grip on. Not having this right could cost a load of pottery, a kiln,
> your studio, your house, your life.
>
> I was going to write a lengthy essay about this - BUT - I found the
> link
> below and I can't even come close to what is presented in such a
> coherent way. >>>
John,
Thanks for taking the time to post this information. There are lots
of repairs I'm willing to do around my home and studio rather than
hiring someone. Electrical work is not one. It scares the hell out of
me. Other than changing the plug on a 110 outlet or a switch to a
light I call the electrician. I have one who has become very
knowledgeable about kilns. There are lots of them in Ann Arbor. I
just don't think it's worth risking my life for something I don't
have any competence in. Gas-now that's a different story. I've piped
every kiln I've ever built. I don't think any book is going to teach
ME how to do electric. It might help me understand, but this is one
place where I'll spend the money for a pro.
Kathi
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