Kiln circuit sizing

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ritelec

ritelec

Senior Member
Location
Jersey
Hello.
I confused myself.

A kiln in a residence. 240v 40 amp

Ok. 40a @ 125% = 50 amp

There's a 6 wire coming out of the unit with what looks like a 50amp 3 wire plug.

I'll be running 6-2 nm on a 50 amp breaker to a 50 amp recpt.

80% of 50 is 40 which is the actual amperage.

This is correct right?

I'm alittle confused because I thought for years that the amps where multiplied by 125% and that number couldn't be more than 80% of the breaker.
Verifying.

Thank you.
 
ritelec said:
I'm alittle confused because I thought for years that the amps where multiplied by 125% and that number couldn't be more than 80% of the breaker.
Click to expand...

When you multiply a load by 125% you are at 80% of a breaker.

Only continuous loads get multiplied by 125%

A breaker is sized for 100% of non-continuous load + 125% of the continuous load.
 
zbang said:
Firing times can be longer than 12 hours, depending on the kiln and the temperature you're aiming for. Any kiln that needs a 10kw circuit is going to be a continuous load when in use.
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I won't claim to be a kiln expert but if you are aiming for XXX degrees and the unit draws full power during the entire firing time, what assurance do you have that you ever reached XXX degrees? What if next time you run you need an even higher temp? Seems to me it is marginally sized for the application if it never shuts off.

Most heating applications your heat supply is larger then needed. Initial warm up may be at 100% output rate but after reaching setpoint the heat is either cycled as needed or is varied to keep up with the demand necessary to maintain setpoint.
 
Not a kiln expert either but I have worked with a few.

The ones I worked with would run continuous until a disposable temperature sensitive element called a "cone" melted out and that shut the kiln off until the next batch.

Here is a picture I found on the net. it is in the ready to run condiction, when the red thing melts it lets the middle rod drop which activates a switch outside the kiln.

cone-in-kiln-sitter.jpg


Here is a melted one

painting-clay-pots-after.jpg
 
iwire said:
Not a kiln expert either but I have worked with a few.

The ones I worked with would run continuous until a disposable temperature sensitive element called a "cone" melted out and that shut the kiln off until the next batch.

Here is a picture I found on the net. it is in the ready to run condiction, when the red thing melts it lets the middle rod drop which activates a switch outside the kiln.

cone-in-kiln-sitter.jpg


Here is a melted one

painting-clay-pots-after.jpg
Click to expand...
So it apparently runs until a set point (determined by the design of the "cone") is reached, and the heating cycle is done at this point. Is understandable that you don't want to oversize heat element too much and reach set point too fast though.
 
kwired said:
So it apparently runs until a set point (determined by the design of the "cone") is reached, and the heating cycle is done at this point. Is understandable that you don't want to oversize heat element too much and reach set point too fast though.
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The kilns I worked on had knobs with High Med Low Off on them. The cones could be purchased in different ratings as far as I know.

http://www.dickblick.com/products/o...UvBKdJGKratXI2l9UPtjVc2DhoCvSfw_wcB#itemspecs

I guess it is a matter of experience in knowing how hot to make the elements run and how high the final cut out temp should be.
 
iwire said:
The kilns I worked on had knobs with High Med Low Off on them. The cones could be purchased in different ratings as far as I know.

http://www.dickblick.com/products/o...UvBKdJGKratXI2l9UPtjVc2DhoCvSfw_wcB#itemspecs

I guess it is a matter of experience in knowing how hot to make the elements run and how high the final cut out temp should be.
Click to expand...

Your scarring me.

Installing for an older friend.

He has a wood working studio in his basement and wants to start working with coloring glass with this kiln

Hope he doesn't burn his house down.
 
ritelec said:
Your scarring me.

Installing for an older friend.

He has a wood working studio in his basement and wants to start working with coloring glass with this kiln

Hope he doesn't burn his house down.
Click to expand...

Do realize that those kilns can fire up to 2400+ degrees F. They are meant for pottery and bisque, not glass.

I used to repair them for schools many years ago. I never heard of one starting a fire, but I also haven't heard of them being used for glass.
 
iwire said:
I guess it is a matter of experience in knowing how hot to make the elements run and how high the final cut out temp should be.
Click to expand...

Besides fixing kilns, my mother had one. Usually people would join a craft type shop that had pottery classes and learn to make pottery there. That's where they learn the temps to fire with and how long the run should be. Then, once they get to where they can make pottery without breaking it, they would go buy their own kilns and do pottery at home.

Usually you deal with 2 temps. One for the first firing which is done to turn the wet clay from the molds into hard ceramic, then a second, higher temp is used for glazing, which is painted on after the ceramic pieces have cooled.

The temps depend on the size of the pieces and the types of glazing used.
 
K8MHZ said:
Do realize that those kilns can fire up to 2400+ degrees F. They are meant for pottery and bisque, not glass.

I used to repair them for schools many years ago. I never heard of one starting a fire, but I also haven't heard of them being used for glass.
Click to expand...

I checked out the link you provided, and the site says that technically there are kilns that do both. Since glass fires at a lower temperature than ceramics, you may be able to use a ceramic kiln for glass, but not vice versa. There are also configuration differences, and a glass kiln MUST have an electronic controller.
 
gadfly56 said:
I checked out the link you provided, and the site says that technically there are kilns that do both. Since glass fires at a lower temperature than ceramics, you may be able to use a ceramic kiln for glass, but not vice versa. There are also configuration differences, and a glass kiln MUST have an electronic controller.
Click to expand...

Thanks!

I have been out of that end of the business for decades, way before electronic controllers were used. They had regular oven controllers back then that had 10 marks (HI being in the place of 10) and a Dawson Kiln Sitter with a timer.
 
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