Why is the amperage of a kiln higher than the rating when a kiln is first turned on?

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  • See the Sales FAQs for Frequently Asked Sales and Preorder Questions
  • The Knowledgebase is organized into a series of questions and answers having to do mostly with technical troubleshooting and understanding of kilns.
  • Although we write this for our own kilns many of these articles apply to other makes - although L&L takes no responsibility for that.
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  • Actions are specific actions for you to take during the troubleshooting or repair process.
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Why is the amperage of a kiln higher than the rating when a kiln is first turned on?

When you first turn on a kiln and the elements are cold the
amperage is higher. Once the elements heat up the resistance changes by
about 4% and the amperage goes down. That is the meaning of "Hot
Amperage" and "Cold Amperage" and "Hot Resistance" and "Cold
Resistance".



What normally matters is the "hot resistance" because the
"hot amperage" is what a kiln normally draws so this is what the electrical circuit normally
sees. The "cold resistance" only lasts for a few minutes - normally under
the time that a fuse or circuit breaker might trip.

Additional Actions to Take

  1. Look for the nameplate data. Plug the amperage and voltage labeled here into Ohm's Law to see what the resistance for the whole kiln should be. If the nameplate is missing you can email the factory to try and figure out what model it is. Measure the inside dimensions of the kiln, take whatever resistance readings you can, let us know whether it has Hi-Med-Low switches on infinite type switches and describe anything else you can about the kiln. An emailed digital picture can be very helpful.
  2. Measure the total resistance of the kiln. Unplug the kiln or turn off the power if you cannot unplug it when measuring resistance in these circuits. Now turn all switches to high, and turn the kiln-sitter on. Measure the ohms from the prongs on the main power cord–-from the two "hot" blades, not from the ground or neutral. If there is a reading, it should be within 9% of what was calculated with Ohm's Law. The resistance can only be lower than what the nameplate calculations would indicate if the wrong elements were installed in the kiln or the elements are so old that they are squashed into each corner all the way around the kiln. Look for overheated connection if low resistance continues for any length of time and replace elements immediately
  3. Measure the resistance of each branch circuit. Turn the switches OFF. The switches must be off or the meter will read all the branch circuits at once. Measure branch circuit resistance with the kiln power OFF from the two flat prongs (not the ground) of the plug-heads of each kiln section. On other kilns you want to determine how many elements are in each circuit and how the elements in each circuit connect together and to each circuit's power wires. Take the branch circuit resistance reading at the point where the power wires connect to the element(s).
  4. Determine series or parallel. Look to see if the elements are wired in series or in parallel with each other. Even in L&L's latest kilns you would still have to either take the element box off or look at the kiln's wiring diagram to determine this.
  5. Check individual element resistance. Try to get a single element's resistance reading by either calculating it if they are in parallel or by measuring it with the meter if they are in series. You may need to disconnect wires to isolate as much as possible of each element.
  6. Take a voltage reading in each branch circuit at either the element connection to the power wires or at the control box receptacles on later L&Ls. Measure the voltage at the main power supply. If there is a considerable voltage drop from the main power supply to the element connection to the power wires then there is a corrosion or connection problem. Badly corroded connections need to be replaced immediately. Both parts of the connection should be replaced at the same time. Check your plug and receptacle connections, especially the main power cord and receptacle.
  7. If the measured resistance is slightly more than 9% over the calculated resistance and this correlates with the problem (slow kiln), you should ideally replace all the elements, or at least those with readings that are too high. If you do not replace them all at once the kiln may heat unevenly (this is much less of problem with kilns having the zoned design with ungraded elements rather than with kilns that have graded elements.
  8. If all of the element resistances are fine but the resistance of the whole kiln is not, the problem must be in a branch circuit. 
  9. With the kiln on, run a voltage test on the receptacles or at the connections to each element in each branch circuit to see which is the bad one.
  10. With the power off, open the control panel and visually inspect the branch circuits. Check branch fuses if the kiln has them.
  11. Locate the two wires that begin the bad branch circuit from the bunch that come from L1 and L2 on the main power block.
  12. Follow those wires to where they connect to the first component in line, probably either a fuse block, a relay or a switch.
  13. With the power ON, and any kiln-sitters or switches on High (so that the elements would come on if they could), take a voltage reading at the point where these two wires connect to the first component in line. The reading normally should be the same as what it is at the main power block. If it is not, one of the wires between the main power block and the first component is bad and needs to be replaced.
  14. If there is voltage there then take another reading after the first component at the point where the two wires continue onto the next component or to the element connection. If there is voltage after the component then the component is working.
  15. To determine whether the contactor or the switch is bad, first follow the wires from the load side of the switch to the contactor. 
  16. With the power all on and the switch on high, take a voltage reading where the two wires from the switch to the contactor connect to the contactor. If these readings are the same, then the contactor is bad.
  17. If there is no voltage present, then follow those two wires back up to the load side of the switch and measure the voltage there. If the voltage readings are the same, then the contactor is bad.
  18. If there is no voltage present, then follow those two wires back up to the load side of the switch and measure the voltage there. If the voltage reading is the same, then one of the wires is bad.
  19. If there is no voltage present at the load side of the switch (power all on, switch on high, then be sure voltage is coming to the switch; if it is, then the switch is bad. Replace the switch and if the problem still persists then repeat the test; you will most likely have to replace the contactor as well.
  20. If there is no voltage after the first component in line and it is not a relay/contactor, then just replace it. If it is a fuse holder, just replace the fuse (usually a bad fuse means there is a short somewhere in the circuit). Use a "continuity" tester to test for bad fuses. Always check tightness of connections in a questionable circuit.
  21. If there is voltage after the first component then move along the circuit from the main power block towards the element connections, testing for voltage before and after every component until you isolate the problem. Voltage readings taken from between the elements (and from between resistors in general) give a reading that reflects voltage which is half the supply voltage with two elements in series, and either one-third or two-thirds the supply voltage with three elements in series (depending on which side of the middle element in the series the test lead is placed).

Resistance and Error 1

  • 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.
  • When resistance, measured in Ohms, increases, both Watts and Amperes (amount of power) will decrease, assuming Voltage remains constant. If you don't have enough power, your kiln will fire slowly and might not even reach the desired temperature.

What does this mean?

  • 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 many cone 6 firings 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 14%).
  • 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).

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.

CHECKING RESISTANCE ON AJUPITER OR DAVINCI KILN

See this tutorial on how to use a multimeter.

Ohms Per ELEMENT VS Ohms per SECTION (or Circuit).

  • 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 on your wiring diagram and divide by the number of elements per section.

Example #1 (2 Elements in Parallel): e23T 240V 1 Phase: Elements are 28.9 Ohms each. Divide by two because they are in parallel and you will get a reading of 14.5 Ohms per section.

    Parallel element connection for a kiln with two elements

    Example #2 (2 Elements in Series): e18S 240V 1 Phase: Elements are 9.6 Ohms each. Multiply by two because they are in series and you will get a reading of 19.2 Ohms per section.

    Series element connection for a kiln with two elements

    Example #3 (3 Elements in Parallel): JD2927 240V 1 Phase: Elements are 36.5 Ohms each. Divide by three because they are in parallel and you will get a reading of 12.3 Ohms per section.

    Parallel element connection for a kiln with three elements

    Example #4(3 Elements in Series): Doll DLH11-DBX 240V 1 Phase: Elements are 6.6 Ohms each. Multiply by three because they are in series and you will get a reading of 19.8 Ohms per section.

    Series element connection for a kiln with three elements

  1. Empty the kiln.
  2. Turn kiln on using a fast program such as FAST GLAZE (USr3) until elements are red.
  3. Open the door carefully and check if each of the elements are glowing with approximately the same brightness.
  4. This is an approximate method. The best thing to do is check the ohms on each element or circuit.

CAUTION: The power does not turn off when the lid is opened. Do NOT put your hand inside the kiln while it is on.

  1. Check your voltage at the receptacle or at your fused disconnect box. Check voltage at your panel and where the kiln is connected. Check the voltage when the kiln is firing and when it is not firing.
  2. Make sure no other large electrical appliances such as a clothes dryer or electric oven are on when you are operating your kiln.
  3. Find out from your local utility company when the end of the peak period of electrical use is.
  4. Check to see what the wire size of your circuit is. If it is very far (more than 50 feet) from your main circuit box then the wire size might need to be higher.

  1. Unplug kiln.
  2. Remove the Control Box.
  3. Using a 3/8" nut driver or ratchet wrench or adjustable wrench, remove the nuts that hold the element end onto the Element Terminal Bolt. Note that the terminal bolt head is held in place by an inset shape on the underside of the ceramic terminal block and it will not turn much.
  4. Untwist the element end from around the Element Terminal Bolt. Straighten it out as much as possible.
  5. In most cases the element can be lifted out of the holder at this point. Sometimes, if the element has really disintegrated, you need to remove it in pieces with needle nose pliers.
  6. If element is hard to get out of the holders (because of growth of the element) you can try heating up the kiln slightly so as to heat up the element slightly to just the point where element is slightly pliable–don't let it get red. This will soften the wire. Then turn off the kiln and disconnect all power to the kiln. Using heat protecting gloves and a pair of needle nose pliers pull out the softened element.
  7. From the inside of the kiln, using needle nose pliers, grab the element as close to where it goes through the brick wall to Terminal Block. Pull the element end through the hole. Be careful not to enlarge the hole in firebrick. The brick is soft and will not take much abrasion.
  8. Be sure to check for failure points for evidence of contamination on the element and the element holder. If the element holder is contaminated it will cause rapid failure of the new element. Replace contaminated holders with the new ones.
  9. Using your multimeter check the resistance of the new element.
  10. Install the twisted ends of the elements through the holes in the wall of the kiln. Element ends should be straight at this point.
  11. Pull them up tight up to the wall of the kiln by pulling from outside the kiln.
  12. Lay the element into the groove. Note that the unfired element is going to have some springiness to it before it is fired for the first time. You may need to use a screwdriver to press the element into the holder. YOU DO NOT NEED PINS.
  13. FOR KILNS WITH NON-CERAMIC TERMINAL BLOCK OR ON RETROFITTED KILNS WHERE YOU HAVE ADDED A CERAMIC TERMINAL BLOCK BUT STILL NEED BUSHINGS: Be sure to replace the insulators and spacers over the element tails.
  14. Consulting your picture or labeling, wrap the appropriate element tails around the appropriate element connection bolt, clockwise, one around and cut off the excess tail.
  15. Install the elements and hardware: Place the wires from the jumper cord or connecting wires onto the appropriate bolts and tighten with stainless steel nuts.
  16. A washer goes under the first element.
  17. Twist the first element end CLOCKWISE around the Terminal Bolt.
  18. The next element gets twisted around the Terminal Bolt on top of the first element.
  19. Another washer goes over the Terminal Bolt.
  20. Place a nut on top and tighten it.
  21. Put another washer on.
  22. Put on the Ring Terminal of the Power Lead Wire.
  23. Put another washer on.
  24. Put another nut on and tighten it. How much the nut can be tightened is dependent on how tight the element connection bolt is on the element connection board. A tight connection is very important, but if you tighten too much and twist the element on the bolt too far you could break the element, the bolt, or the insulator.
  25. Reattach the ground wires and the element box if the kiln has them. DO NOT FORGET TO ATTACH GROUND WIRES. IF EACH KILN SECTION IS NOT GROUNDED THIS CAN BE VERY DANGEROUS.
  26. Test the resistance at the jumper cord's plug head or at the other end of the connecting wires.
  27. Reattach the control box, turn on the kiln and make sure all the elements come on.

See this tutorial on how to use a multimeter.

See this video: