The electrical data plate, which is mounted to the side of the switch box on most kilns, lists the kiln's rated amperage. As the heating elements age, they pull fewer amps. Measuring the amps is one way to determine if the elements are beginning to age.
However, a low amperage reading does not always indicate worn out elements. The low reading could also be due to low voltage. To correctly interpret the amperage reading, first take a voltage reading of the circuit that powers the kiln.
Here is a useful formula:
Voltage tested with a voltmeter while the kiln is firing divided by the circuit's rated voltage = ratio of loss
Ratio of loss multiplied by the kiln's rated amps = expected amperage of a kiln fired at this new voltage
Example:A 240-volt kiln is rated at 45 amps (10,800 watts). The 240-volt circuit gives a voltmeter reading of 240 volts. If the voltage reading drops to 235 while the kiln is firing, then
235 divided by 240 = 0.979
45 amps x 0.979 = 44 amps
44 amps is the normal amperage of a new 45-amp kiln fired on the 235-volt circuit.
44 amps x 235 volts = 10,340 watts. The normal wattage for this particular kiln on 240 volts is 10,800, but because of low voltage, the kiln will draw only 10,340 watts.
This example shows how low voltage affects the amperage reading. This is why a voltage reading should be taken before the amperage reading. Wattage is directly proportional to the maximum temperature that can be obtained; i.e., lower wattage results in a lower maximum temperature.
