Easy Access Kiln Switch Box
Copyright (c) 2001 by Beverly Howard, Austin, TX, USA

Some Tips on Rebuilding the Electrical Components on a Studio Potter's Electric Kiln.

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.

The traditional electric kiln switch box design is a practical approach to building a new kiln.  In general, it holds all of the element switches facing away from the kiln and the mounting box also provides a safety enclosure to insulate the supply and connecting wires away from anyone working at or near the kiln.

In the manufacturing scenario of a brand new kiln, the entire switch/wiring enclosure is built separately and populated with switches and connecting leads.  When the kiln chamber is ready and the elements installed, the leads from the completed switch box are attached to the heating element pigtails protruding through the kiln wall, the wires stuffed inside, and the switch box (or boxes) are screwed to the exterior kiln wall directly over the exposed element pigtails.

That efficient production design is not, however, the best when it comes time to replace a defective element or to rewire a kiln.  Due to the high temperatures kilns are subject to, the wires, connectors, insulation and switches quickly age and become fragile.  Corrosive gasses attack the metal box structure and fasteners leading to the case where attempts to repair any electrical components can easily lead stressing and breaking other connections resulting in yet more problems.

The kilns in the pictures are old, the younger of the two is fifteen years, the older over twenty, and both have been rewired at least 10 times each indicating the fact that they have been constantly active in a production studio that fires only oxidation and uses only these two overworked puppies.

This first picture shows my first switch box rebuild that has now been in use for about two and a half years.  All of the materials used for the rebuild are standard aluminum stock and screen which should be available in any good hardware store.  My personal construction philosophy in projects like this is to make something that will get the job done and not necessarily look good, hence the rough edges you will probably spot.  The instructions are also not 100% complete, but should be obvious when working with the components from a production kiln... i.e. how to mount the lead coming from the kiln sitter.

The primary component in the revised structure is a piece of 2 1/2 inch aluminum angle cut to the height of the kiln.  All of the switches will be mounted in this piece and this piece, in turn, will be mounted, as shown, well to one side of the element pigtail exit holes in the kiln wall.  I used aluminum "U" channel to mount the angle about an inch away from the kiln surface to provide a cooling channel behind the aluminum switch mount.

You have probably already noticed that the switches shown are simple toggle switches in place of the standard oven type "Variable" controls mounted on most kilns.  These "variable switches" can be mounted in the same holes.  (The kilns pictured are controlled by a computer driven main switch that is not in the picture, so variable controls are not necessary)

By mounting the switches off to one side, the path from the element pigtails to each switch is both direct and free from any interference from the wires feeding the other element switches.  The supply wires from the contact block mounted at the bottom of the angle are bundled and routed between the switches and the aluminum angle.  These supply wires are the original high temperature wires supplied with the kilns when they were new.

I elected to mount the switches facing the kiln sitter to shield them from accidental tripping, but they could be mounted on the other side of the elements as well as long as you take into consideration the fact that you will probably need to provide a longer connection from the kiln sitter.

In this first box design, I stayed with the traditional concept of running wire from the switches to the pigtail leads connected with screw down contact blocks, but in these pictures you can see that I ran the pigtails directly to the switches and connected them with blade connectors crimped directly to the element wires... almost, since I had wound the coils before this job, the bottom elements wouldn't reach, so they have wire lead connections and are not in sequence... sigh.

In the traditional box design, the box itself provides the safety cage around 220 volts of potentially life threatening "gotcha" but at the cost of rendering maintenance access difficult and dangerous.

In this design, all components remain mounted during any maintenance access, so the safety cover is a completely separate piece.  If you have access to the same steel mesh that the manufacturer used, it will provide a stiffer construct that the aluminum screen door protector mesh that I used.  The huge benefit is that this cover easily removes by removing a handful of sheet metal screws and the removal has zero impact on the wiring and components behind it.

To form the basic cage, use a length of 2x4 with the mesh on a table or floor and fold up the basic box using the 2x4 to form a square edge.  On the ends, make only one cut before folding, the use the overlap and bend the cut wires into the mating mesh to close the corners.

Since the aluminum mesh needs additional strength for safety, take three 1 1/2" lengths of aluminum bar stock and form strengtheners who's ends will also provide mounting tabs.  Place these at about the one quarter marks and fasten them behind the mesh with large headed pop rivets.  If you elect to use bolts, make sure they do no protrude far enough to make contact with the elements if someone leans on the cage and deflects it.

Note that I only used two mesh stiffeners in the first box, but elected to go for the additional stiffness and safety of three in the second.

A bonus discovery this time... the kiln shown needed to have the insulation plates replaced.  This design was so old that it had individual (probably asbestos) squares held in place by porcelain buttons, and I didn't have time to order a replacement.  It happened that we were mounting some bathroom tiles and I guessed that "Hardy Board" tile backing might work.  I took a welding torch to a piece and it didn't seem to care.  I took an ohmmeter to it to confirm that it wasn't going to conduct electricity and when it passed that test, I cut a 1/4" piece to size and drilled the element holes and it's doing great.  Note, also, you can see the aluminum screen door protector mesh that will be used to build the protector in the background.

Beverly Howard... Responses, implementations, comments and suggestions appreciated.  Email me at Bev@BevHoward.com

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