There's been some talk on the forum lately about new kilns and appropriate breaker/fuse sizes, so I thought I'd share an odd experience I had today with a customer's kiln.
I was doing a checkup on an older Paragon (pre-1994) with the oldest digital controller I'd ever seen. It had an old phone pad for the buttons- only the second one of those I'd ever seen. There was no cone fire mode, only custom program, and that would only allow one step- X rate of climb to Y degrees and off. So no slow heating with a faster climb in the middle or slowing at the end or anything like that. So that was pretty neat to see.
But the main reason I'm writing is to discuss the voltage situation at the customer's house. I checked the service voltage to her kiln and it read 259 volts! It should be at 240, give or take 3 or 4 degrees. Typically when I see high voltage it's 245-248. The most I'd ever seen was 251. So this was crazy high.
This was a big deal because the electrician who wired up the outlet for the kiln put in a 50 amp breaker. If this had been a normal 23x27 kiln that pulled 48 amps at 240 volts, it would have pulled close to 52 amps at 259 volts- too much for the 50 amp breaker. The customer's kiln was rated for 45 amps at 240 volts, so at the higher amperage it would be just barely under 50 amps, but still very likely to flip the breaker.
Electrical code says that resistance heating appliances like kilns should be on a breaker that s 25% greater than the actual draw of the kiln, so a 45 amp kiln should be on a 56.25 amp breaker, which doesn't exist, so you go up to the next size which is 60 amps. 48 amp kilns also need 60 amp breakers, although I have several customers who run them on 50 amps without problem, but clearly their voltage isn't too high.
You really can't control how high the voltage is, short of calling your electrical company and demanding that they do something about it, which they most likely will not do. However, I did suggest to my customer today that she call them because the voltage is so very high, and could possibly be a sign of a problem in the system somewhere. And she needs to call her electrician and have a larger breaker put in, which could also mean larger wire if they did not use wiring large enough for 60 amp service.