Pottery Kiln

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nizak

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I have a small electric kiln that my customer would like hooked up.

Nameplate is 1P 90A 240V

The unit is quite old and has no operating manual or any instructions.

Owner has 208V available . Can it be safely operated at the lesser voltage?
I made him aware that the temperature output would be less.

Any help appreciated.
 
It can be operated but does the label state 208-240 volts?
The kw will be reduced.
Simple solution is an auto transformer
 
A lot of customers with kilns prefer the lower voltage, and have me install a buck/boost transformer to drop the voltage. It is because the heating elements supposedly last longer, but it does take longer to heat up.
 
90A is hardly a small kiln. The "workhorse" size pottery kiln commonly used in schools and similar situations is 48A.

Most manufacturers have 240V and 208V heating elements available and it's just a matter of swapping elements when changing from one supply voltage to the other. I know a few years ago, the conductor material used to make the elements was one of those supply-chain items that became near-impossible to get, and the kiln vendors pushed out the lead times significantly. This was a problem because the elements are wear items that must be replaced once enough metal boils off and their resistance becomes high enough that they stop heating effectively.
 
BarryO said:
90A is hardly a small kiln. The "workhorse" size pottery kiln commonly used in schools and similar situations is 48A.

Most manufacturers have 240V and 208V heating elements available and it's just a matter of swapping elements when changing from one supply voltage to the other. I know a few years ago, the conductor material used to make the elements was one of those supply-chain items that became near-impossible to get, and the kiln vendors pushed out the lead times significantly. This was a problem because the elements are wear items that must be replaced once enough metal boils off and their resistance becomes high enough that they stop heating effectively.
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I don’t know if different voltage elements are available for this kiln.

I believe the manufacturer went out of business in the mid 80’s.
 
If it’s that old, it may be all mechanical, so it probably has a multi tap control transformer that only needs the tap moved to change the voltage. The elements are not that picky.
 
My baby sister has one that I ran a 100 amp feeder down to the syrup mill for. She bought it new about 15 years ago, and has never used it! She is an elementary art teacher. At least I got power to my gate out of it. LOL!
 
When he said old, I was picturing my mother's 1930 something kiln with its cloth covered cord and strange looking 240 volt plug
 
I think this is what you meant, but it is the heat output that will be less. Thermostat controlled, so the temperature will be the same, just that it will take longer to get up to temp.
 
Jim Reizner said:
I think this is what you meant, but it is the heat output that will be less. Thermostat controlled, so the temperature will be the same, just that it will take longer to get up to temp.
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Yes longer to heat up and fire. I had wired a killed at a senior center. It was 240 on a 208 V supply and we got a lot of complaints about how long it took. We get a question often on this formum about using 208 on 240 and 240 on 208, electricians understand that, but others don’t.
 
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I did a calculation multiplying the 90 amps by 80% = 72 amps @240 volts single phase & 17,280 watts. At 208 volts it would be 62.4 amps & 12,979 watts. It has been many years since I had to run a line to a Kiln but it was always under 60 amps. So at the reduced 208 volts it would only produce 75% of the BTU'S of heat. Reduced voltage will never damaged a purely resistive load. Even if the customer had a 400 amp service if a 72 or 90 amp load was energised I would think all the lights in the building would blink. Cannot remember the KW size that kicks In requiring at least two banks of heater elements in say electric unit heaters. The shops that I installed kiln power would turn them on just before closing then set a timer and by morning timer timed out so guessing I'd a full vo!tage kiln ( 240 volts say ) needed 8 hours running it on a 25% BTU reduction might take several more hours if the desired temperature could be obtained.
 
Jim Reizner said:
I think this is what you meant, but it is the heat output that will be less. Thermostat controlled, so the temperature will be the same, just that it will take longer to get up to temp.
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The older ones didn't have a thermostat. They were controlled by a mechanical mechanism called a "kiln sitter". The mechanism held a 1-time-use small pyrometric cone that was made to go soft and bend at a specified temperature. When the cone bent, this allowed a switch to open and kill the power to the heating elements. Yes running 240V elements on 208V would just increase the ramp time, provided the firing temperature wasn't so high that it was never reached with the higher resistance elements.

Kilns available today monitor temperature with a themocouple and are computer controlled. Potters can now specify firing programs with certain ramp-up, hold, ramp-down, etc., times. If the ramp up time is outside of spec the computer detects that something is wrong, throws an error message, and stops the program. The customer looks in the manual and is told they need to have someone replace the elements and/or the relays. So in general, 240V elements won't work on 208V.
During COVID I found a place in Canada that made aftermarket elements. I'll see if I can find the name.
 
BarryO said:
During COVID I found a place in Canada that made aftermarket elements. I'll see if I can find the name.
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Well it's not in Canada but post #9 already has an link to an outfit that can supply elements and most other parts of old kilns. I did have to modify some bricks that didn't have direct replacements available though.
 
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