Kiln wiring difference between 208 volts and 240 volts

[Nancyk]

I have an Olympic Kiln Model 2827H that I believe went to the original owner wired for 240V. She had a fire in the electrical box on the kiln and replaced it and the control box with refurbished boxes. I believe that she also converted to 208V because the instruction manual has 240V crossed out and 208V handwritten next to it.  She was in a commercial building so I think that is why she changed. Now I have the kiln in the basement of my home and it is plugged into a 6-50R receptacle on a 60 amp breaker with a 240V residential box. 

The kiln has been firing ok for a year or so, but now is not getting to temp and erroring out. I'm wondering if I have to convert the kiln's electrical box back to 240V and if so, what the wiring might look like. I will call Olympic on Monday, but I wondered if any of you have any input that would help. I don't fully understand electrical issues, but my husband does and could rewire it for me if we knew what the wiring should look like.  Then again, will getting new elements for 240V fix the problem?

I'm trying to learn as much as I can to understand the situation better. 

Thank you!

[Dick White]

Your issue is not in the electrical box, but in the elements. The resistance of the elements must be matched to the voltage to generate the same amount of heat. Elements designed for 240V but run on a 208V circuit will never generate as much heat, and likely not get past bisque temperatures. Aside from whatever caused the fire, that is why she installed elements appropriate for the 208V location. Now you have moved it back to a 240V location. The 208V elements are going to overheat and wear out sooner. The overheating isn't a big problem, as the electronic controller will call for only as much heat as needed to raise the kiln temperature according to the program. But the elements wearing out sooner could be the reason it is now not reaching temperature and throwing errors. Everything in the control box will be the same whether running on 208V or 240V, so there is nothing to change there.

[Nancyk]

Thank you so much!

[Bill Kielb]

I would double check the control transformer and make sure the it is configured for 240 v. Many transformers will have a reasonable working range and some will have a jumper or multiple taps to configure for 208v service. Just a precaution to check so your control transformer lasts a long time at 240 v in the event it was tapped at 208v previously. There will be some labeling on the transformer as to which leads should be connected.

A kiln tech, electrician or someone reasonably handy with electrical wiring could help confirm. In the example below the red wire is used for 208v service and the orange for 240v. Running it on 240 v using the 208 v tap will reduce its lifespan and put out more voltage to the controller than needed also potentially reducing the life of the control. All unused taps on the transformer get electrically capped   and taped neatly so the bare wire of that tap does not touch anything metal.

 

[Dick White]

Another possibility for the control transformer used in many kilns is a 120V -> 24V double tapped (i.e., 2 @ 12V) transformer. These operate on one leg of the 208 or 240 main power, which will always be 120V to ground regardless of the voltage across both legs powering the elements. The Bartlett and Orton control boards need two 12V power leads, hence the need for the double tapped transformer.

[Bill Kielb]

42 minutes ago, Dick White said:

These operate on one leg of the 208 or 240 main power, which will always be 120V to ground regardless of the voltage across both legs powering the elements.

Yes, makes sense, the transformer I picked above was just to illustrate the different primary voltage taps. Most kilns will have a 24 v center tapped secondary.  Most kilns don’t use a neutral anymore though so I think a good thing to just double check and make sure the primary is tapped at 240v in this case.