Electricity is LETHAL! The following information is provided for those who are knowledgeable, experienced and comfortable working with and around 240 volt ac electrical systems and high temperature ceramic kilns. If you are not, please do not attempt to implement any of the following suggestions without the help and assistance of a licensed electrician.
In addition to the electrical dangers, electrical and firing problems can easily lead to accidental fires that can destroy structures not to mention the possibility of killing or injuring people. While the author has executed the following modifications and those modifications are currently in use in a full time pottery studio at the time of this writing, the author does not accept any responsibility for any injury, damage or other losses that may result from attempting to implement any of the suggestions and designs shown in the following page. The use and implementation of these suggestions are at your own risk.
I have spent my life working with electricity and electrical circuits. Some of my most vivid childhood memories are of being jolted by a full dose of house current. Even so, the first time I looked at the wiring on a kiln I was intimidated. I can see how the idea of rewiring an electric kiln could be overwhelming to most potters, but, as I found out, it is not as difficult as you might think. When you have been through it once, the lessons learned can reduce subsequent rewiring times to the point that element and switch replacement can be thought of more as regular maintenance than as a major project.
In addition to replacing the worn-out elements, the kiln can also be upgraded with some of the improvements that you now find on the newer models. A Kaowool blanket can be placed between the switches and the kiln wall to increase switch and wire life. Old style element connector posts can, and should, be replaced with the newer screw clamp types. Ceramic guide straws can be inserted through the kiln wall to make future wirings easier and protect the firebrick.
Before the disassembly begins, it is best to have the elements, and any other components that you know will have to be replaced, on hand. Also have information on where other replacement parts can be quickly obtained. In addition to having the ceramics suppliers and kiln manufacturers as a source for the elements and other replacement parts, knowing alternate sources for parts can save both time and money.
Specialty companies will supply standard and custom-wound elements, and the variable switches used on most kilns are standard items that are used on electric stoves and heaters, available at appliance supply houses. The push-on type connectors have been standard for two decades. The same holds true for the supply wire and wall outlets, which are available at any wholesale electric supply.
When ordering the elements, have both the model number and the electrical data available to assure getting the correct elements. The heating elements for any kiln design are available for either 110 volts or 220 volts. The manufacturer may design a kiln using only 110-volt elements so that with simple switch wiring changes, the kiln can be set up for either voltage. Crusader, for example, uses pairs of 110 volt elements wired in series to make one 220 volt heating unit. Wiring a 110 volt element directly to 220 volts will produce spectacular but disastrous results.
For replacement switches and other components, it is best to take one of the original components with you while you shop as the part number used by the kiln manufacturer will be different from the component's part number.
The Right Tools
Good tools will make the job easier and safer. Here is the minimum you will need;
Volt/Ohm Meter The Volt/Ohm Meter has two important uses for the potter. The first is to detect and measure voltage and the second is to check resistance which will confirm a connection when testing a dead circuit. The simplest (about $8) will work, but the resistance of a heating element will be on the order of 20 ohms (very little) so having a digital meter (about $30) set to the 2-k/ohm scale will help the troubleshooting process greatly.
Diagonal Wire Cutters These should be big enough to to allow you to clip the twisted ends off the elements easily. Too small and the extra effort and movement required to cut the elements may cause damage to kiln walls or asbestos cover plates. End- or plier-type cutters will not allow you to cut wire in confined spaces like firebrick slots.
These are necessary to make a good electrical connection between the push-on connector and the high temperature wire. Crimping electrical connections with pliers will not make a good connection.
Screwdrivers, pliers, and a Crescent wrench will be necessary.
The screws that you remove will not be reusable, but replacements should be available at any hardware store. If there is a marine supply nearby, replacement with stainless hardware will help the next time around. The contact blocks are the only electrical component that will be hard to find locally, and the best source may be your kiln manufacturer.
Stripping The Kiln
The first step is to disconnect the kiln from the power supply. If the kiln is wired directly to the box, turn the breaker off and padlock the breaker box closed. Electricity is a life and death matter and it is foolish to rely on verbal cautions or paper notes to others. First, inspect the plug. If it is discolored or burned, both the plug and wall receptacle should be replaced. Cleaning the prongs will provide only a short term solution because the spring tension in the wall receptacle has probably been lost due to the heat generated by the poor connection.
Next, remove the box covering the connections to the elements. Make either detailed photographs or a diagram of the connections. On a kiln with infinitely variable switches, each switch will probably have four connectors (Figure 1). Two of these will lead to the ends of an element or element pair, and the other two will be connected to the power source, usually coming from the Kiln Sitter box. The wires from the power cord are connected to the posts marked L1 and L2, and the heating element(s) to H1 and H2. There may be another post (P) for a pilot light. If there is no pilot light, it doesn't have to be connected.
If wires are broken or break as you remove the box, look carefully at the location of the broken wires before you disturb them further. The heat normally sets their shape and they will remain close to the location where they broke.
After you have a record of the wiring, use a pair of cutters and cut the old element wire at each place where it exits the kiln. Use large enough cutters and brace your hands on the kiln to avoid damage to the firebrick and asbestos cover panels. Keep the clamp-type connectors unless they are badly corroded.
If the connections are made at the kiln wall with a nut and 28 bolt arrangement, they will probably not be reusable and care must be taken not to break the asbestos mounting blocks. By trying to remove the nuts with a wrench, the bolts will probably shear flush with the bottom nut and can be left in place. Once the wires have been cut, you can place the switch box to one side.
Next, take a pair of heavy diagonal cutters and, from inside the kiln, cut the element free at the last coil. Remove all the coils, but keep at least one intact to use it as a length measurement for stretching the new coils. Use caution as you work to keep from breaking the ledges cut in the firebrick, particularly at the bottom of the kiln. The cut off leads should be easy to remove through the kiln wall.
Inspect the high-temperature connecting wires in the connection box. These are covered with a high-temperature insulation and cannot be replaced with wire covered . with anything less. If the wire can be pulled out of the push-on connectors, the connectors should be replaced. The connecting wires will generally be much longer than necessary. If the connector needs to be replaced on either end, cut off about half an inch arid strip about a quarter inch of insulation.
Replacement push-on connectors are available at appliance supply houses as well as at automotive, electronic, or hardware stores. Take an old connector with you to avoid lengthy descriptions. These connectors are "crimped" onto the end of the wire. (Again, don't use pliers for crimping.)
Replace any switches, wires, and other parts as needed at this time. If you are new at wiring, replace one component at a time to reduce the chances of wiring mistakes. Replacement switches may have an extra post for connection to a pilot light that can simply be ignored. Look for burned or loose contact posts by comparing the old switches to a good one. Any switch that makes a "sizzling" sound at any time during a firing should be tossed out.
If you wind your own elements, be sure to twist two strands of heating wire together at each end of the coil to connect the pigtails. By twisting two element wires together, the resistance is lowered and the heat produced in the pigtail will be halved, reducing the stress on the element-to-wire connection.
Stretch the new coils slightly longer (1 to 3 inches) than the old coil length. This will take several tries as the coil will slowly shrink back a couple of inches after each stretch.
Using The Volt/Ohm Meter
The only tool used during the reassembly and checkout procedure that is likely to be unfamiliar to most potters is the Volt/Ohm Meter. All of the checks described below are made with the meter set as an ohmmeter at the most sensitive setting. At this setting with the test leads not touching anything, the reading will show a high resistance, and when they are touched to each other, the meter will show contact by registering 0 ohms.
To use the meter to check an element, for example, the leads are touched to opposite ends of the element. If the element is good, the meter will show a low reading. If the element is broken at any point, the reading will be high, the same reading as with the leads touching nothing.
With this meter, it is then possible to check for the correct wiring before the power is connected. It is also possible to check for any short circuits before sparks have a chance to fly.
Putting It Back Together
First, insert the twisted leads through the ceramic straws or wall openings. Starting on one side, carefully replace the new coils in the brick slots and move around the kiln. There will be a bulge of coil left, so start back in the other direction, gently compressing the coils to work the bulge out by the time you get three quarters of the way back to the starting point.
Gently seat the coils into the grooves. Because the coils have been stretched long, the tension will hold them in place until after the first firing, after which the seating should be checked again. Continue until all the elements have been installed.
If the coils were wired in pairs, the next step is to connect the pairs.
Check with your photos or Figure 2 to confirm the correct wiring. If you
have any tendency toward dyslexia, as I do, making mistakes here is easy.
Hold the element lead with a pair of needlenose pliers where it exits from
the kiln, and bend the element ends to be connected
together neatly so they lie as close to the kiln wall as possible.
Make the connections with screw clamp contact blocks then clip off any excess element wire. The results of your wiring should be symmetrical with the last coils connecting just like the first. With the ohmmeter, check to make sure there is no connection (no change in the meter reading) between each element and the metal parts of the kiln. If you have a digital meter, make a reading of the resistance of each coil or pair.
The readings should all be equal. If not, check the connections again. Place the old (or new) Kaowool blanket over the protruding element ends. With the switch enclosure supported on a box or stool to hold it close to its mounted position, begin to connect the wires from the switches to the element ends as close to the blanket as possible. Work slowly and methodically, starting at either the top or bottom and connect only one switch at a time.
Clip off any excess element wire after the connection is made. After each switch is connected, use the photos or diagrams to confirm the wiring. Once all of the connections have been made and double checked, carefully move the switch enclosure into place.
Check up and down the entire height for connecting wires that may be pushed against a hot surface like the kiln wall or the ends of elements. Check also for contact blocks or bare wires that may be too close to or in contact with the connectors on the back of switches. Also check for contact blocks touching the side of the enclosure or wires pinched between the switch box and the kiln.
Mount the enclosure with new screws top and bottom.
1. Turn all of the element switches to "Off and the Kiln Sitter "On.'
2. Using an ohmmeter or continuity checker, check first between the two supply lines or prongs on the plug, then between each supply line and the ground line. The meter should show no connection between any of the wires or prongs.
3. Check to confirm that there is a connection between the ground line and the kiln or switch enclosure casing. (Ground is the green or bare wire.)
4. Connect the ohmmeter to the two supply lines. Turn each switch on and off to confirm that each makes a connection. If you have a digital meter, the resistance should equal the reading you made before connecting the switches.
5. Turn all switches on and confirm that there is no connection between either supply line and ground.
6. Trip the Kiln-Sitter to "Off and confirm that there is no connection between the two supply lines. Check again that there is no connection between either line and ground.
If any of the above tests fails, it's time to go back and check the wiring again. If the failure occurred in a specific switch test, it should be easy to trace it by starting at that switch. By disconnecting the switch, you can determine on which side of the switch the problem is. Don't forget that the switch could be defective even if it is brand new.
The First Power Up
When the tests all pass, turn all switches off and reconnect the kiln to the power. Turn the Kiln Sitter on and turn each switch on "High" individually. You should be able to first hear, then smell the element heating.
Turn the switch "Off and test the next one.
Replace the remainder of the switch-box mounting screws.
Assuming everything went well, be careful with your first firing using the new elements. The performance of the old elements degraded too slowly to be noticed.
The temperatures during the first firings will come up much more quickly
than you are used to and peak temperatures will be reached hours earlier.
Failure to monitor the temperature and cut-off closely could result in
a lost load or even the loss of the kiln in the event of a Kiln Sitter