How can I protect an existing power supply?

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  • 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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How can I protect an existing power supply?

Circuit Breakers

  • Circuit breakers that have tripped and have been reset continually will be more apt to trip at a lower amperage than they are rated for. They get worn out.
  • A breaker in a small kiln room will trip sooner because of the higher ambient temperature.
  • An inductive amp meter will indicate whether the kiln is pulling more amperage than the breaker allows.
  • Remember to size it for 125% of the total amp load.

Wire Size Too Small

  • Using a wire size that is too small for the amperage draw will cause the wire and conduit to heat up and the voltage to the kiln will drop.
  • Voltage will be lost in the form of heat.  The breaker can trip from the local heat.
  • Without a properly sized breaker, the connection points can start to corrode and this may cause an electrical fire.


  • Any visible corrosion in an electrical circuit- especially on a plug and receptacle connection - will result in heat generated at that point.
  • Heat leads to corrosion, which leads to more heat and eventually the melting of the component or connection point.
  • This could start a fire if the breaker fails to trip.

Dedicated Circuit

  • The kiln should be on its own circuit. If anything else is on the circuit the voltage will drop when the other device is turned on.
  • The circuit breaker must be rated for more than the combined amperage of all the devices if the kiln must share a circuit.

Melting power cord

  • Look for the power cord melting if it is close to the kiln.
  • Look at the receptacle that it plugs into for signs of overheating; these include bulging, discolored, swollen.
  • Look for flattened insulation (like a small slice from the side of the cord). This is where the cord came up against the side of the hot kiln but for whatever reason, did not stay there long. If the cord is only very slightly melted it may be OK to use if the situation that caused the melting is rectified.
  • If the cord appears to be getting worse, or gets hot when the kiln is firing, replace it. If the insulation on the cord has deteriorated it is possible that the power wires could short out and cause a fire.

Additional Actions to Take

  1. Make sure power cord is plugged in.
  2. Reseat the plug. Pull it out of the receptacle and put it back it. This will reseat the connections.
  3. Also, sometimes the female socket and/or the male spades get oxidized (which can resist the flow of electricity). Reseating them can disturb this oxide layer.
  4. When you do this examine the plugs for any signs of burning or overheating. If the spades look oxidized you can rub them with steel wool to shine them.
  5. Make sure the plug is held firmly and that the springs inside the receptacle seem to be working.
  6. Look for any damage on the cord itself.
  7. Make sure the cord is not touching the kiln case.

CAUTION: This test should only be done by an experienced person familiar with electricity and its dangers.

  1. Unplug kiln or turn off circuit breaker if the kiln is wired direct to your power supply. If you can not physically be sure the power is disconnected (for instance is you see that the cord is unplugged you KNOW there is no power coming into the kiln) then check the voltage at the power connection pluck with your multi-meter.
  2. Open up the control panel. This will be a little different on each kiln series.
  3. Remove or open the panels that cover the element connections.
  4. Look at internal wiring.
  5. Images burned wires in a kiln

  6. Check the tightness of all connections. Do this by wiggling the connector to make sure nothing is loose.
  7. Make sure all wires are connected to their proper connection point. You may have to compare the kiln to the wiring diagram to be sure of this. This step would be particularly important if a wire has come loose.
  8. Specifically look at wires going from power connection block to the on/off switch, then to the control fuse, and finally to the control transformer.
  9. Make sure all wires inside control panel are connected.
  10. Look for any burned spots or deteriorating wire.
  11. Look for any short circuits. This might be caused by a wire losing its insulation and touching another component for instance. Typically if there are any short circuits there will be some evidence of a burn on the metal the wire touched.
  12. Look for dirt or foreign material. Some material can be an electrical conductor and could cause a short circuit. Clean out any dirt.
  13. Pull off and reseat all spade connector connections of power wires to remove oxides and ensure good connection.

CAUTION: Turn power off to kiln from the circuit breaker or unplug the kiln.

  1. Make sure the circuit breaker or fused disconnect switch is turned on.
  2. If you have a circuit breaker flip it back and forth to make sure that it is really on. Some circuit breakers, if they have tripped, will not be obviously in a tripped position. By flipping it back and forth you will reset the circuit breaker.
  3. Check voltage of your power supply at the receptacle using your multi-meter set to the next highest AC voltage above 240 (typically this will be 600 volts but may be 250)
  4. Check fuses for voltage continuity. You can do this with your multi-meter.
  5. Make sure fuses or circuit breaker are/is the proper amperage and type. See your wiring diagram for the required fuse type.

CAUTION: This test should only be done by an experienced person familiar with electricity.