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My kilns have recently stopped firing and it need new elements. I have to buy elements for specific voltage/phase combination. I didn't install the kilns - it was done by my studio mate before they left - so I am trying to sort it out. They are hard-wired into a breaker box, each of which has 3 breakers ganged up. The panel has other circuits on it that are standard outlets, so I am trying to establish if the kilns are 208 single phase, 208 three phase, or 240? I am ruling out 240 because of the fact that there are three breakers -- it seems more likely that it is 208 3 phase. Any thoughts?

To complicate matters, one kiln has '208 single phase' written on it and the other has '240 single phase' written on it. However, these kilns can be rewired and I don't know their provenance, so I don't trust the labels (thanks old studio mate for not writing the wiring down!). I will also contact the manufacturer but that could take weeks.

The kilns are Skutt km1227 and km10247.

This is in a shared studio that was historically a commercial space.

Here's the panel -- it looks like it says 3 phase, 4 wire, 120V - so that makes me think it is 208V 3PH?

Sadly I am at home now an don't have a picture of the breakers, themselves. That would have been a good idea.

The wiring is thick black shielded cable, one cable for each kiln.

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Thanks for any insight.

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    Any of the following may help to figure this out: Model # of kiln; picture of breakers; picture of wiring going into kiln – manassehkatz-Reinstate Monica Oct 17 '18 at 0:31
  • Can you measure voltages as well? – ThreePhaseEel Oct 17 '18 at 0:34
  • @ThreePhaseEel Because the kilns are hard wired, and the breaker box is closed up, I don't have access to the power. – Steven Oct 17 '18 at 0:38
  • @Steven -- do you have access to receptacles fed from more than one circuit in that panel? – ThreePhaseEel Oct 17 '18 at 3:48
  • @ThreePhaseEel I don't recall seeing anything that a standard 120V outlet. I will check next time I am there. – Steven Oct 17 '18 at 23:34
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Shut off the breakers, and open the access panel on the kilns, and then examine what is connected to what, with great care, and a kiln manual in hand. Skutt has good manuals, in my experience.

Since they can be wired in many different ways, and may no longer match the "as shipped from factory" condition or the "as Sharpied by someone, sometime" condition, you have several options. As you are presently in a studio with 3-phase power available, unless you anticipate moving to a studio without three phase power available, it would be an ideal time to wire them as 3-phase when replacing the elements, if they are not presently so wired. If they currently connect to triplexed breakers in a 3-phase panel, odds are very good that they are already wired that way - but examining what is connect to what will tell the truth.

You could also check the labeling on the kiln-sitter and/or fancier computer control unit, if so equipped. The original factory voltage/phase configuration should be stamped into a steel plate on the kiln itself, as well.

Finally, if in doubt, hire a competent electrician or kiln technician (your ceramics supplier will either have one or know one) if you are not confident of getting it right yourself. Being sure is worth it on something this critical, and it sounds like you let "your old studio mate" handle this in the past without being directly involved yourself. Pay attention to what they do, and why, and document anything that needs documenting.

If the "time to element failure" is not quite a few years, also review the kiln operators manual and be sure that you are conforming to good operating procedures for best element/insulation lifetime. They should last quite a long time.

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  • Thanks for your answer. Next time I'm at the studio I'll have another look inside the controller. I had it open to measure the element resistance today but didn't know exactly where the power came in - I guess now it was behind some fiber insulation. – Steven Oct 17 '18 at 3:05
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That panel is 208/120V 3 phase 4 wire for sure. If it were 240/120V 3 phase 4 wire, the circuit count would be 40/80 instead of 42/84 because you lose a couple of pole spaces in the B phase restrictions. If breakers are 3 poles and ganged, it is a 3 phase feed. But even so, if your Kilns say they are single phase, someone could have just USED a 3 pole breaker because it was already there and only used 2 of the 3 poles. Nothing technically wrong with that.

If you are sure that the kilns only need single phase, you can use 2 pole breakers. If you are replacing the elements, use 208V elements if you want fast response, because 240V elements will run with less heat and take longer to get to temperature. But if you want them to last longer, use 240V elements.

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  • I'd think you'd lose more than 2 spaces to not being able to use the B-phase for single-phase loads, or maybe you could explain that more? – ThreePhaseEel Jun 18 '19 at 0:26
  • I used to work for Siemens, but it's been a while so I'm going by memory here.It has to do with how their breakers plug into the bus and that in a 240/120 3 phase 4 wire "High Leg" delta panel configuration, you cannot use a single pole breaker on B phase. So in a 42 space panel, you have 14 pole spaces per phase, but 14 is not evenly divisible by 3, so you can only use 12 spaces on B phase for 3 pole breakers, but if you mix 2 pole and 3 pole, you will not come out right. So Siemens restricts you from using the top and bottom pole on B phase if it is High Leg delta, thus 40 poles vs 42. – JRaef Jun 18 '19 at 20:06

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