Testing Element Resistance

Testing Element Resistance

Click on image to enlarge

INTRODUCTION TO RESISTANCE

The most common cause of kiln slowdown, E-1 messages, and failure to reach temperature is element wear. As your elements age  they generally increase in electrical resistance. According to Ohm's Law, when resistance, measured in Ohms, increases, both Watts and Amperes will decrease, assuming Voltage remains constant. Since Amps and Watts are the measures of current and power respectively, they can be thought of as the amount of juice that your kiln has to generate heat. Obviously if you don't have enough power, your kiln will fire slowly and might not even reach the desired temperature.

INTERPRETING RESULTS

Using resistance, we can tell exactly how much power your kiln has lost over the course of your element's life. For example on an e23T that uses 240V, a brand new kiln section would read about 14.5 ohms. If you measured this same kiln section after several months of cone 6 firings let's say and the reading was 16.5 Ohms, you would know that this section of elements has lost approximately 14% of it's power (16.5/14.5=1.138, or close to a 14% increase). Again, an increase in resistance means decrease in power. A very general rule of thumb is that most people will typically begin to notice some slowdown once you've lost more than 10% of your power. It will certainly vary based on the kiln you have, your voltage, as the types of firing you do. People only doing low fire work will continue to get by on lower power than those needing to go to higher temperatures (cone 6+). As you can see, measuring your element Ohms is the best way to identify when elements need replacing.

Keep in mind that the ohms on the wiring diagram are per ELEMENT while your reading will be per SECTION. How you figure out the section ohms depends on whether the elements are wired in Parallel or Series. Most kilns are wired in Parallel except for JD230V and most 18" kilns like the e18T. For a parallel kiln you take the per element ohms listed and divide by the number of elements per section. Ex. e23T 240V 1 Phase is 28.9 Ω per element with two elements per ring = 14.5 Ω per section.   Ex. 2. JD2927 240V is 36.5 Ω per element w/ three elements per ring = 12.2 Ω per section. See this link for more info on Series vs. Parallel

Here we will show how to best measure your element resistance for two groups of L&L Kilns, into which most models fall.

EASY-FIRE, DURA-FIRE, EQUAD-PRO, LIBERTY-BELLE, DOLL, SCHOOL MASTER

In these series' of kilns a piggy-backed control panel covers up the element terminals.

  1. Turn the power to the kiln completely OFF and unplug it if possible. If it is direct wired, then you should at least turn off all power at the disconnect switch or circuit breaker.
  2. Open the outermost control panel by unscrewing it either from the element cover box in the case of Easy-Fire, eQuad Pro, School Master and Liberty Belle kilns or from the kiln body in the case of Doll kilns.
  3. Once you open up that control panel you will see the element power wire terminal strip. See the picture. It will have numbered wires coming from the element terminal blocks and wires connecting to the power relays. There are two wires per kiln section/ring, so numbers 1 & 2 are for the top section, 3 & 4 for the middle, and 5 & 6 for the bottom section on a three ring kiln.
  4. Set your multimeter to Ohms (Omega symbol Ω) and using your testing leads, place one in between the two tabs/terminals w/ #1 wires connected. There is a small circular divot that the lead fits into (see picture). Put the other lead on terminal #2 and make note of the reading. Repeat the process for 3 & 4 and then for 5 & 6. Remember that each pair of wires represents one section.
  5. Compare your readings to those on the wiring diagram in your instruction manual. Keep in mind that the ohms on the wiring diagram are per ELEMENT while your reading will be per SECTION. See above for more info on understanding the readings.

CHECKING RESISTANCE ON AN EASY-FIRE KILN

JUPITER, DAVINCI

In these series' of kilns, the control panel is separated from the kiln body and the element terminals are connected to the controls via external jumper cords or plugs.

  1. Turn the power to the kiln completely OFF and unplug it if possible. If it is direct wired, then you should at least turn off all power at the disconnect switch or circuit breaker.
  2. Unplug the first jumper cord from the control panel.
  3. Set your multimeter to Ohms (Omega symbol Ω) and using your testing leads, place one lead on each of the "hot" prongs. They will be the flat ones.
  4. Make note of the reading and move on to the next one.
  5. Compare your readings to those on the wiring diagram in your instruction manual. Keep in mind that the ohms on the wiring diagram are per ELEMENT while your reading will be per SECTION. See above for more info on understanding the readings.

See this tutorial on how to use a multimeter.