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When a Kiln Slows Down

If your kiln slows down because of low voltage, turn off other large appliances while the kiln fires.


When a Kiln Slows Down

Reader Response: 15 and 20 amp receptacles

Recent Q&As: Solid state relays

A Kiln Story: Mice in the Kiln Room

Memorable Quote



Low voltage can double the firing time. If your kiln is firing too slowly, make sure the voltage listed on the kiln’s electrical data plate matches the voltage of the electric circuit. (The electrical data plate is usually located on the side of the kiln or the switch box.) Firing a 240 volt kiln on 208 volts reduces the kiln’s power by 25%.

Low voltage has the same effect as firing with worn out elements. Even a small drop in voltage can slow down your kiln. For example, we test-fired a 120 volt kiln that took 5 hours and 3 minutes to reach 2331°F (1277°C). On a separate electric circuit, the same test kiln took only 2 hours and 30 minutes to reach 2350°F (1287°C). The difference in voltage between the two circuits? Only 7 volts.

If your kiln ever slows down temporarily, do not assume that it is due to worn elements. The voltage to your building may have dropped due to peak demand. Have an electrician check the voltage under load (while the kiln is firing). Until you know the voltage, an amp reading of the kiln won’t tell you much, because low voltage also causes low amperage.

If the voltage is low during a period of peak demand, fire your kiln when the electrical demand is lower and the voltage is higher. Fire at night or early morning. Also, turn off other large electrical appliances such as a clothes dryer while the kiln is firing.

Another reason your kiln may be firing slowly is that the firing chamber may have too much moisture. Firing moist ceramic greenware or moist glass molds can slow down the kiln. Dry these materials before firing them.

For the recommended circuit wire size, consult your local electric codes and the kiln’s electrical specs at your kiln manufacturer’s website. Install the kiln within 25’ (7.62 m) of the breaker or fuse panel. For every additional 50’ (15.24 m) from the panel, increase the circuit wire size by one gauge. This helps to reduce voltage drop.

If the kiln still fires too slowly after following the suggestions above, have the power company check your voltage and readjust the transformer for your area if necessary.

A digital controller will show error messages when it has been programmed at a faster rate than the kiln is capable of firing. This can happen even when voltage is normal and the kiln is new. You may be using a firing schedule that is designed for a faster kiln. In this case, program a slower rate.



Last week’s Kiln Pointer explained the difference between 15 amp and 20 amp, 120 volt wall outlets. Tony Rodriguez of San Antonio, Texas wrote, “It would be nice to explain the reason for the difference in the 15 amp and 20 amp receptacles. If you were able to plug something that requires a 20 amp breaker into a 15 amp receptacle, the breaker would trip to the off position. The circuit wire gauge requirements are also different.”



Q. What types of solid state relays do the Sentry and Sentry Xpress controllers support?

A. The Sentry 12-key and 3-key controllers can be used with solid state relays that have a DC volt control signal input in the range of 12-15 volts DC. (Many solid state relays have an input range of 3-32 volts DC.)



From an interview with Brenda Griffith, author of “Kiln-Formed Glass: Beyond the Basics”

“I did production work for shows and had to fire 24 hours a day to get enough work done. Because there weren’t computer controllers then, I would have to set my alarm so I could get up throughout the night to change the settings on the kilns. At the time I lived in a coach house above the garage of an old house in the Kenwood neighborhood of Hyde Park. The kilns were in a little room under the stairs, so I would get up, put on a robe, and patter down the stairs to adjust the kilns, note the time and temp of each in my log books, and then shuffle back to bed to reset the alarm and do it all again.

“It wasn’t bad in the summer, but in the winter the garage under the coach house wasn’t heated, and the mice would hang out in the kiln area to keep warm. So I would often go from half asleep to screamingly awake in seconds when one would run over my foot.”

You can read the rest of the interview here:



“The most important thing in communication is hearing what isn’t said.” --Peter Drucker


We are holding a Basic Kiln Maintenance Seminar tomorrow and Saturday. We cleaned the factory for the occasion. Amidst the whining of a vacuum cleaner, the office has been bustling with students arriving early. John Hohenshelt, Sr. and David Snyder will teach the seminar.

David sat relaxing with me after his flight from North Carolina. Bright sunlight from a large window cast a warm glow in the room. I said, “Every time I attend a seminar, or even hear some of it from another room, I learn something new.”

“That’s why I’ve come back to this seminar so many times,” he said. “Every time I come, I learn something new. I pick up nuggets of gold that I take home with me.” David has attended our kiln seminars for over 20 years.

Thank you,

With best wishes,

Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd., Mesquite, Texas 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 / / /

PRIVACY NOTICE: Under no circumstance do we share or sell your email address.

Copyright 2014, by Paragon Industries, L.P.

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