Electricity - things to consider with kilns

Ok, just wanted to share some general info because more and more of us are working with the electric kilns. First, I love to use analogies because they can help explain the unfamiliar things with everyday familiar items that we can all relate to.
First thing to consider is safety. It’s not perfect but flowing water is a good analogy for electricity. There are two things we are concerned about, the first is volume (opposites would be Mississippi River and Denton creek), in electrical terms that’s voltage. The other concern is the current (think class5 white water rapids opposed to a gentle meadow brook), this is Amps in electric terms.
Most people think the hazard is the volts which is wrong, a typical static shock from carpet is 2000-4000 volts! The hazard is the current. The minimum current that can cause a fatal shock is only 150mA (milliamperes), that’s a little over 1/10th of an Amp! Now consider the max current the kiln is usually rated at is around 50A, hundreds of times the level of a fatal shock. So, whenever working on a kiln the first thing to do is unplug it!


I would word this as the minimum amount that is almost guaranteed to kill is around 150mA. You can die from as little as 10ish mA. Every human is different.

It’s the volts that jolts but the mills that kills.

I’ve had a few 120VAC shocks before. With old cooper that’s corroded slightly it’s a deceptive tingle not unlike 24VAC. With a new out of the box limit switch that you brush your hand against inside an appliance chassis it’s like a bee sting.

But those experiences were nothing like what a lawnmower can do. Was mowing the folks lawn decades ago and the mower was not staying started. Finally realized that the spark plugs wires wasn’t firmly attached. Had the presence of mind not to touch the metal contact - grabbing about ½" down the wire from there - but it wasn’t enough and that entire side of my body convulsed a couple of times before the engine stalled. Thankfully ignitions generate thousands of volts but very little current and I was otherwise unharmed.


the last component is frequency. The lower it is - the closer it approaches DC - the more it hurts. We were working on a live telephony equipment when an automatic dialer placed a call. Got zapped by the ringer voltage which is only 12v, around 10 hZ. Let me tell ya, that hurt more than any 120v 60hz zap I’ve ever gotten. So…don’t do that. cheers!

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Good point, also assumes the shock is across the heart which is going to be the case (hand to hand across the heart) probably 80% of the time.

So…don’t stick your hand in the toaster while it is plugged in?


How else do you get the toast out?


Open circuit voltage on a telephone line is 48vdc. Depending on what standard you read, ringer voltage is 75 to 110V. But yeah, it is a different type of bite.

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Was once working a troubling FIOS install late at night with an exhausted field tech at the customer prem. After finally coaxing the ONT to activate then provision I was doing some testing with the last test being a ​BORSCHT test.

Asked the tech if they were ready. Tech indicated affirmative. Asked if they had their buttset plugged in. They said they did. So I kicked off the test … about 2½ seconds into the ~5 second test the tech howled like they’d been stung - seems they’d been in contact with the leads on the buttset. Technician was far more alert during the call wrapup.


Actually, that’ll zing you but you’d really have to work on it for injury.

One Sunday morning when I was 8 or 9, my folks are sleeping in late, and I made myself some toast, which refused to come out of the toaster. I went to ask Mom what to do, and she mumbled “Get it out with a fork”. So I climbed onto the counter, and stuck a fork into the toaster. Zinged me up to about my elbow, but that was it. And now I am much more cautious about handling live electrical equipment.

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Yeah, that’s what I said :grimacing:

There are two more concepts resistance, this is the elements in the kiln and is measured in unit ohm (Ω). Back to my water analogy, resistance works like handle on your sink, turn it open for a small flow is the same as high resistance, the valve only allows a little to pass or if you open it all the way the water blasts out in a jet or low resistance to water flow.
The last one is power measured in watts (w). A simple example is a hand held hair dryer, a 600w dryer will get the job done but 1200w works much faster.
You can use these four (voltage, current, resistance and power) to express how the kiln works with a couple simple equations:

E=IR and P=IE

The (E) is volts, the (I) is the current or amps, the ® is resistance in ( Ω’s) and § is power in watts.

Use 1027 (208vac 1 phase) for example, the element resistance are 11.7 Ω and 14.4 Ω. Using the E=I*R formula, substitute in our values
208 = (I) * 11.7
208 = (I) * 14.4
Do the math and the current works out to 17.7 amps 14.4amps. This is the new elements or the peak current that the kiln will have. The element resistance goes up with usage which means the current drops off over time.
Now power the kiln will have then is:

§ = 17.7 * 208 or 3680w

So what happens to the power when the voltage is low? Hypothetically, it drops to 185vac (about 10% drop) what happens with the kiln.
185 = (I) * 11.7 ( the elements didn’t change) drops the current to 15.8 amps, this drops the power output to 2920. That represents about 20% drop in power!