I am switching my greater than 50 amps manual kiln from 208 volts to 240 volts. What do I need to do to the kiln?

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I am switching my greater than 50 amps manual kiln from 208 volts to 240 volts. What do I need to do to the kiln?

Change Elements

  1. All the elements will need to be replaced.
  2. For example the ohms on the J2927 208 volt element circuits should be around 10.4. If you put 240 volts to each circuit it will pull around 23 amps per circuit- which is too much.
  3. Should not be more than 20 amps per circuit for the J2927 208v kiln.

You May Need To Change Relays

  1. Greater than 50 amp manual kilns were made with voltage specific relays and switches too. It is hard to say what will ultimately happen if you put 240 volts to a 208 volt switch or relay.  The switch might cycle on and off faster and probably burn out more quickly, and the magnetic field created by the relay coil would be stronger than it needed to be and probably burn out the relay sooner. The best thing is to swap these out for the right voltage if the relay coils are not multi-voltage.

  2. If you are switching from 240 volts to 208 volts you will not get to temp if you are trying to get to cone 5. Using the J2927 example- on 208 volts the 240 volt elements will make the kiln draw about 16-1/2 amps per section which is about 20% lower than it should be. Electrically this is ok, but max temp will be about Cone 1.

  3. For the relays and switches you will want to replace the relays. The switches will be ok running on 208 volts. The relays however will produce a smaller magnetic field and may not be able to completely close the relay contacts. When this happens the relay can chatter which quickly overheats the contacts and often fuses them shut allowing the kiln section to remain on High all the time, even when the kiln-sitter is off.

Check Electrical Specifications

  1. Changing voltage sometimes means pulling more amperage. Be sure to check the electrical specs for your kiln as it will be after the change- i.e. if you are changing to 240 volts look for the electrical specs your kiln as a 240 volt kiln. Be sure your breaker and wire size is large enough. Breaker size is determined by the new amp rating of the kiln, multiplied by 1.25 (125%) and then rounded up to the nearest breaker size. Wire size is tied to the breaker size:

20 amps
 12 gauge copper
30 amps 10 gauge copper
40 amps 8 gauge copper
50 amps 6 gauge copper
60 amps 6 gauge copper
70 amps 4 gauge copper
80 amps 3 gauge copper
90 amps 2 gauge copper
100 amps 1 gauge copper
125 amps 1/0 gauge copper (pronounced "one aught")
150 amps 2/0 gauge copper (pronounced "two aught")
175 amps 4/0 gauge copper (pronounced "three aught")
200 amps 250 MCM copper wire (MCM = Thousand Circular Mils)
225 amps   
350 MCM copper wire

Additional Actions to Take

Check Power Relay
  1. One way to easily check relays is to look at the kiln elements through the peepholes when the kiln is firing. If you know your elements are OK after having done an ohm test and the elements are not glowing then you should suspect the relays.
  2. Another way to check the relays (or bad elements) is to check the temperatures of each zone by pressing "1", "2" and "3" in sequence and recording the temperatures of each thermocouple at intervals over the length of the firing. If one zone is consistently firing at a lower temperature then you probably have either burned out elements or a bad relay.
  3. If the relay does not make a soft clicking noise when the kiln is turned on try turning the kiln off and on and then restarting the program.
  4. Remove panel.
  5. Set your multi-meter the approximately 24 volts AC. Check the voltage coming into the coil of the Power Relay. You can tell which wires these are because they will be the small wires coming from the control. This test will tell you if you are getting power to the relay coil which actuates the relay. Unless the relay is actuated by the control you will get no output from the power side of the relay.
  6. With panel plugged in and firing check output from Power Relay with your digital multi-meter. The meter should be set to the next highest voltage above 240 volts AC. Output should be approximately the rated voltage of the kiln when it is supposed to be calling for power to the elements.

CAUTION: LIVE ELECTRICITY IS INVOLVED WITH SOME OF THESE TESTS. This test should only be done by an experienced person familiar with electricity.

See this video:

Checking Elements

EASY-FIRE, DURA-FIRE, EQUAD-PRO, LIBERTY-BELLE

  1. With all power OFF, pace the test leads of the multimeter of the each of two of the terminals marked 1 and 2, 3 and 4, or 5 and 6 on the element terminal strip. Compare the reading you get to the reading you get from the other element terminals. Also check against the wiring diagram for the ohms listing.

JUPITER, DAVINCI

  1. With all power OFF, pace the test leads of the multimeter of the two flat prongs of each section's jumper cord, one on each prong, OR on both connecting wires, at the connection points with the elements. Compare the reading you get to the reading you get from the other jumper cords or connecting wires. Also check against the wiring diagram for the ohms.

See this tutorial on how to use a multimeter.

Examine all wiring for short circuits, bad connections, and burned areas.
  1. Check the tightness of all connections. Do this by wiggling the connector to make sure it is not loose.
  2. Examine all connections for any sign of oxidation or discoloration.
  3. Examine all wires for signs that the wire may have burned.
  4. 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.
  5. Look for any place where a wire may have shorted against the metal case or a component.

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

Replacing Elements
  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:

Replacing Power Relay
  1. Unplug kiln.
  2. Remove the control box and the insulation panel.
  3. Remove the wires to the relay.
  4. Remove the nuts from the studs that hold the relay in place. Remove old relay and replace with new one.
  5. Visually inspect the wire connectors. Do they look corroded or "cooked"? Are the wires frayed? Any corrosion on the wire itself? If any of this is questionable you should replace the appropriate wires.
  6. Reconnect all wires. Visually inspect to make sure the spade connectors are down as far as they can go and feel to see that they are tight (a gentle tug should not remove one). If they are loose for some reason remove the wire and slightly squeeze the spade connector with pliers to tighten it.
  7. See this video.

IMPORTANT: The slip on wire connectors cannot be loose or corroded. If there is a bad connection then heat will be generated and the component that they slip onto (relay, terminal strip, etc) may overheat and fail. If you squeeze the slip on terminal to make it tighter–be sure to squeeze it evenly so that one side is not tight and the other loose. If there are any doubts about the integrity of the wire or the connector replace the whole wire or harness.

Applies to these Kiln Series

Applies to these Old Kiln Series