Kiln as a Continuous Load

[A-1Sparky]

I've got two kilns to wire up, and the literature that I have on them states that they take 8-10 hours to reach maximum operating temperature (2350F). The programmer will limit the temperature to 1800F, but I'm thinking that it will take well over 3 hours to achieve that temperature. So, I'm pretty sure that I have to treat this as a continuous load, but was hoping for some clarification, as the NEC doesn't address kilns as far as I can tell. Thanks in advance.

 

[iwire]

Have a small bit of knowledge of kilns I would call it a continuos load based on the definition found in article 100

 

[A-1Sparky]

Thanks, Iwire. That's what I was thinking too.

 

[K8MHZ]

Have a small bit of knowledge of kilns I would call it a continuos load based on the definition found in article 100

I used to design and build kilns. I would also consider them a continuous load without further information. There may be a model of kiln that cannot be made to run the elements continuously, but I have never seen one.

One design may run the elements continuously until hitting high limit. Another design may cycle the elements until high limit is hit but still may be able to be programmed to to both.

The old Paragons and Crusaders used standard stove control knobs. Set on 1, the would only be on for 1 second in 10. On 10 they would be on for all 10 of the 10 seconds.

If this is a ceramic kiln, the wire elements have a nasty habit of coming out of the grooves and shorting together, which will bump up the current but not necessarily trip the OCPD.

Also, consider the ambient temp. I used to go on service calls where the kilns were in small rooms and it was well over 100 degrees in them.

 

[A-1Sparky]

I used to design and build kilns. I would also consider them a continuous load without further information. There may be a model of kiln that cannot be made to run the elements continuously, but I have never seen one.

One design may run the elements continuously until hitting high limit. Another design may cycle the elements until high limit is hit but still may be able to be programmed to to both.

The old Paragons and Crusaders used standard stove control knobs. Set on 1, the would only be on for 1 second in 10. On 10 they would be on for all 10 of the 10 seconds.

If this is a ceramic kiln, the wire elements have a nasty habit of coming out of the grooves and shorting together, which will bump up the current but not necessarily trip the OCPD.

Also, consider the ambient temp. I used to go on service calls where the kilns were in small rooms and it was well over 100 degrees in them.

Thanks for the input, and yes, I had planned on making an ampacity correction for the increased ambient temperature. One question for you though...would you recommend running 250C insulated conductors for the short run (less than 10 ft) from the disconnect to the kiln. I'm thinking that the wiring enclosure attached to the kiln will get very warm and do not want to have any melting insulation issues.

 

[K8MHZ]

Thanks for the input, and yes, I had planned on making an ampacity correction for the increased ambient temperature. One question for you though...would you recommend running 250C insulated conductors for the short run (less than 10 ft) from the disconnect to the kiln. I'm thinking that the wiring enclosure attached to the kiln will get very warm and do not want to have any melting insulation issues.

250 is overkill. There should be 'glass' conductors going from the elements to the control, which should be heat insulated from the kiln from the manufacturer. Also, the cord should be from the maker as well. I guess my first question is why you are installing the cord? Take a look at Paragon's catalog. All the kilns come with cord and plug installed from the factory.

http://www.paragonkilns.com/current specials.htm

Look for some labeling. If this is a commercially made kiln, there should be conductor info on it somewhere if you are expected to connect directly to the controller. If you can't find specs, contact the manufacturer. If you look close at Paragons's stuff, they don't all use the same type of cords.

We just used SOW for ours, we put enough kaowool between the control panel and the kiln to keep things cool.

 

[A-1Sparky]

These are huge kilns...37KW and 2 tons. I'm planning on running from a local disconnect to the wiring compartment, but was concerned about the temperature inside the compartment, as its basically bolted/welded onto the side of the kiln. On other kilns that I've worked on, I've seen the factory-installed high temp conductors run from the elements to the contactor(s) inside the wiring compartment, and I've seen discolored (heat compromised) insulation on THHN conductors inside the same compartment. I'm trying to avoid any possible future issues. Thanks.

 

[K8MHZ]

These are huge kilns...37KW and 2 tons. I'm planning on running from a local disconnect to the wiring compartment, but was concerned about the temperature inside the compartment, as its basically bolted/welded onto the side of the kiln. On other kilns that I've worked on, I've seen the factory-installed high temp conductors run from the elements to the contactor(s) inside the wiring compartment, and I've seen discolored (heat compromised) insulation on THHN conductors inside the same compartment. I'm trying to avoid any possible future issues. Thanks.

Some of the discoloration may be from a reaction the the out gassing of what ever is being fired in the kiln.

Give Paragon a call. You will probably have to leave a call back number but last I knew they had good tech support. Let the tech know what you are trying to accomplish.

Crusader used to make small kilns, but now are only doing large ones, AFAIK. If you have a Crusader, again, call tech support and get some info from them.

Another good source may be AMACO. http://www.amaco.com/shop/groups-10-kilns.html

Kilns are kind of a niche service. They aren't like heat treat furnaces, which are nearly ubiquitous. When I was servicing kilns there were only two people, me being one, in the entire west side of Michigan that worked on them. I traveled all over fixing them at schools and ceramic shoppes.

I owe a lot to my mentor in the kiln business. He taught me how to figure out everything I needed to know to design kilns, including winding our own elements. My first application of Ohm's Law was doing element lay outs. It sure made my apprenticeship easy in that respect, Ohm's Law was almost a reflex for me by the time I started first year.

 

[A-1Sparky]

Thanks for all the great info! This is actually an Alpine kiln...I've got a tech support number, so Ill probably give them a ring. Thanks again.

Some of the discoloration may be from a reaction the the out gassing of what ever is being fired in the kiln.

Give Paragon a call. You will probably have to leave a call back number but last I knew they had good tech support. Let the tech know what you are trying to accomplish.

Crusader used to make small kilns, but now are only doing large ones, AFAIK. If you have a Crusader, again, call tech support and get some info from them.

Another good source may be AMACO. http://www.amaco.com/shop/groups-10-kilns.html

Kilns are kind of a niche service. They aren't like heat treat furnaces, which are nearly ubiquitous. When I was servicing kilns there were only two people, me being one, in the entire west side of Michigan that worked on them. I traveled all over fixing them at schools and ceramic shoppes.

I owe a lot to my mentor in the kiln business. He taught me how to figure out everything I needed to know to design kilns, including winding our own elements. My first application of Ohm's Law was doing element lay outs. It sure made my apprenticeship easy in that respect, Ohm's Law was almost a reflex for me by the time I started first year.