Pottery Kilns tripping breakers

[mark the sparky]

I posted this question a year ago and you guys didn't get it right...becuase the customer just called and said it is still tripping the breaker.

I have a Pottery Kiln in a shop. Manufacturer specs say to wire it for a 60 amp 240 volt circuit on #6 THHN. I did this and it is tripping the breaker when the kiln kicks to high and thereby doesn't finish the cycle making a bunch of little artists unhappy. Some interesting this to consider.

1. New 400 amp service, 120/208 , 3 phase. (I know it is 208 not 240...there are three other same kilns running on it and they work fine.)

2. Only 6 feet from the panel.

3. Kiln just re-wired with new heating elements.

4. Kiln had a 240 buck boost on it before and still kicked the breaker (which was a 50 at the time).

Fire away guys...give me your thoughts.

 

[tom baker]

Re: Pottery Kilns tripping breakers

Whats the amperage when it trips? a 60 amp breaker won't trip at 60 amps, it may take minutes or longer to trip at 80 amps.

Whats the voltage open curcuit and under load?

 

[bennie]

Re: Pottery Kilns tripping breakers

Is this kiln hard wired with copper conductors?

 

[charlie b]

Re: Pottery Kilns tripping breakers

Originally posted by mark the sparky: ? and you guys didn't get it right....

That?s a bit harsh. If I didn?t issue any design drawings under my own PE seal, and if no other member of this forum personally visited the site, studied the configuration, and issued a recommendation, they we can?t be answerable for ?getting it right.? All we can do is take the information stated in the original posting as if it were gospel, and offer our best professional opinions. If we don?t get it right, then perhaps we didn?t have all the facts at our disposal, and had no hope of getting it right.

Here?s my contribution to the issue: Does the manufacturer?s literature (?specs?) tell you how much load, in KVA (not KW - kilns can have inductive heaters), the kiln will draw at its high setting? From what I remember of my mother?s pottery days, the kilns often ran for more than three hours. The NEC would call this a ?continuous load.? So whatever the manufacturer might recommend, the NEC requires that you design the branch circuit and its overcurrent protection device for 25% more than the load.

Also, please keep this in mind: If four people are blindfolded and then escorted to the very brink of a cliff, and if only one falls off, it is not appropriate to conclude that the other three are safe, and that there was something wrong with the one who fell. You say that three other kilns have the same power source and have not tripped. I say that it is possible that they will someday. Without a thorough analysis of the installation, I would certainly not yet conclude that the problem is limited to the one that tripped.

 

[bennie]

Re: Pottery Kilns tripping breakers

Charlie B: Excellent response. This kiln appears to be the unit closest to the service and breaker.

I would investigate the heat, from the kiln, cummuting to the breaker. The old law of physics everything must reach equilibrium, will eventually overheat the breaker.

 

[charlie b]

Re: Pottery Kilns tripping breakers

Bennie: Now that?s what I call ?thinking outside the box.? I was thinking only of electrical considerations. You also found a mechanical (i.e., heat transfer) possibility. Good job!

 

[charlie]

Re: Pottery Kilns tripping breakers

What are the ampere readings on the circuit when it kicks into high gear. If the heating element has just been replaced, was it cut to the right length for the applied voltage? Since this is only six feet from the panelboard, what is the actual voltage? If the transformer is on the nose of the service and/or is close to a substation, you may have high voltage.

As far as a continuous load, after reaching its firing temperature, it will cycle just like an oven, WH, etc.

I hope we are getting it right, without all the information and my crystal ball on the fritz; I would hate to get it wrong. :roll:

 

[bennie]

Re: Pottery Kilns tripping breakers

My crystal ball does not have event capture . I have been involved on two fire calls, from overheated kiln circuits. The wiring was within the code requirements.

The heating elements are rated at 230 volts, when on 240 they will carry more current.

Most kilns are not wired for continuous operation. The high temperatures required for glazing, will keep the elements on for a long period of time.

Everything can be within the code requirements but the conductors will attempt to reach the temperature of the elements. This is why the 125% is applied to continuous loads. The conductors, and associated equipment, create their own ambient temperature.

 

[gregoryfast]

Re: Pottery Kilns tripping breakers

If the kiln is rated at 60 Amps at 240 volts, that would be 14,400 volt amps. If you are supplying it with 208 volts, 14,400/208 = 69 amps. I think it would actually be even higher, as the efficiency of the coil will go down at a lower voltage.

 

[charlie]

Re: Pottery Kilns tripping breakers

Gregory, you are calculating too fast <snicker, snicker, LOL>. If this were a motor, the amperage draw would go up as the voltage went down. I suspect this is totally a resistance load and the amperage draw would down up as the voltage went down.

 

[charlie b]

Re: Pottery Kilns tripping breakers

Charlie:

It could go either way. That's why I mentioned earlier that the heating system may be inductive. Lacking the manufacturer's data, we can only guess.

 

[gwz2]

Re: Pottery Kilns tripping breakers

The electric kilns thatI am aware of have what is called a "KILN SITTER" installed on the Unit.
This kiln sitter is a mechanical trip to shut off the power when a certain temperature is obtained. The mechanical trip is a device in which a "cone" is installed on the mechanical trip supports. When the temperature within the kiln reaches the temperature at which the cone sags and allows the trip mechanisim to open the power to the kiln.

Depending on the "cone" rating some kilns take at least 6 hours and they do not cycle on and off. These are well over the 3 Hour continuious load of the NEC.

I really doubt that there is much inductive load on each heating unit. Again, the one's I know of, have a spiral wound resistance wire ( about 3/8" in diameter) and are approximates 7 foot long. with either 5 or six heating units per kiln .

Bennie could easliy have the 'CB trip point pegged' if the kiln is close to the panelboard.

 

[iwire]

Re: Pottery Kilns tripping breakers

As far as a continuous load, after reaching its firing temperature, it will cycle just like an oven, WH, etc.

The only kilns I have been envolved with did not cycle like an oven, the heat ran continuous until the time was complete.

There was no thermostat as we think of one, they had a spot to put in a piece of ceramic (I think they called it a cone) between two fingers and when the piece melted the kiln shut down.

[ June 25, 2003, 04:54 PM: Message edited by: iwire ]

 

[charlie]

Re: Pottery Kilns tripping breakers

As I have stated before, there is a lot to learn. Thanks guys, I assumed this would work like an oven.

 

[mark the sparky]

Re: Pottery Kilns tripping breakers

Charle B...my man...take a deep cleansing breath...it was a joke man...just a joke...sorry I forgot to write "it's a joke" and decorate the post with cute little faces.....did you get harmed as a child? (sorry another joke...please don't reply!) I mean please stay away from cliffs with three other people...or kilns for that matter...you can never tell what a kiln is thinking!

The kiln is #2 of four in a row all within 15 feet of the panel...all wired the same way, cord and plug connected on 50 amp range receptacles. This one was a problem child before the service change...the old panel board was trashed and nearly burnt up.

Just because the manufacturer says to put it on a 60 amp breaker...doesn't mean it should pull 69 amps. That is manu. specs. I had it on a 50 right after the COS and it did the same thing. Just for the record, the other kilns are on 50 amp breakers. This kiln is pulling at least 20% more than the others...don't you think that is curious?

As far as the other kilns potentially being "a problem in the making" Then isn't all electrical equipment in the same class? I am saying that to say this...there is a problem with THIS KILN and I need to find out what it is...not burn "X" free troubleshooting hours on the other kilns "potential problems"...this customer will not go for that...and quite frankly I don't want to open that can of worms for HER (emphasis on HER) to worry over. Unfortunately, I am very busy right now, and really don't have the "extra time" to run over across Denver Metro to sit for 12 hours while the kiln hits "high" and wait for the problem to occurr. This is why I came to the experts...I mean all our brains from all across the country...all these college edumakatin's and degrees has to produce an "easy answer"...right!?!? (Again Charlie B, that was a tongue in cheek comment...please don't be offended!)

 

[bennie]

Re: Pottery Kilns tripping breakers

Lets do this the old fashioned way...Think about it

What does the nameplate have for voltage and watts? What is the watt rating of the new element.
It is obvious that this one kiln is drawing more than the others.

Get a wheatstone bridge and read the resistance of the heating element. Compare it with one that is OK.

Get a thermo-skan of the panel with the kiln on for an hour or so.

Have you switched places with the breakers and connections?

Gather all the data and this problem is a piece of cake.

 

[roger]

Re: Pottery Kilns tripping breakers

If Bennies suggestion doesn't work, scan the schematics and post them here, or somewhere we can see them. Then someone can walk you through the trouble shooting process.

Roger

 

[gwz2]

Re: Pottery Kilns tripping breakers

When replacing the heating elements, it is important to use the elements supplied by THAT kiln manufacturer for that model number.

3 phase and 1 phase kiln elements are not interchangable with-out the manufacture's input.

The heating elements are not all the same resistance per length.

Is it possible that the heating element have be replaced by improper ones?

Sorta appears to me, this may be the starting point.

The total amperage should not be more than the
nameplate value.

When starting, the amperage may be 3 to 5 amps high until the elements heat-up which is usually less than 3 to 4 minutes.

I would suggest contacting the manufacture with your problem an just install new element per his ratings.

Probably cheaper than all the suggested test equipment. Although, the prices of the elements more than doubled in the last three years.

 

[charlie b]

Re: Pottery Kilns tripping breakers

Originally posted by mark the sparky:Charle B...my man...take a deep cleansing breath...it was a joke man...just a joke...

I was not offended in any way. And please be assured that the two fully armed nuclear missiles currently converging on your position are just a courtesy we provide to our more good-humored clients. Just a joke! Please don?t call Homeland Security. I was merely mis-quoting from ?The Hitchhiker?s Guide to the Galaxy.?

With regard to the remaining three blindfolded persons on the brink of the cliff, I did not mean that a large share of the troubleshooting budget should be focused on the kilns that have not tripped. What I intended was that we should not be blind to the possibility that the source of a problem might lie beyond the component that is conspicuous from its having already failed.

 

[iwire]

Re: Pottery Kilns tripping breakers

Originally posted by charlie b:
please be assured that the two fully armed nuclear missiles currently converging on your position are just a courtesy we provide to our more good-humored clients.

Mental note, do not mess with Charlie.