Kiln Room Wiring

Now that you’ve confirmed your power supply with an electrician and ordered your kiln from your local distributor (https://skutt.com/shop/distributor-locator/), it’s time to get the wiring installed. 

When the electrician comes to your home to install the wiring and receptacle for your kiln, you should inform him or her of the following important information recommended for your kiln:

  • Copper wire gauge
  • Receptacle style
  • Location of outlet
  • Circuit breaker size

It is important to hire a licensed and qualified electrician to install the recommended wiring components for your new kiln.  It is also critical for your electrician to know that the kiln voltage must match the voltage at your home.  Kilns are not like many other electrical appliances or motors that the electrician is familiar with.  Kilns will typically not operate properly on a range of power supplies like other appliances are able to.  The voltage at your home should be measured at within +/- 3% of the kiln’s rated voltage.  For example, if the kiln is wired for 240 volts, it is designed to work properly on supplied voltage that is between 232-247 volts. 

Two of the most common kiln firing problems that we encounter are related to mismatched voltage between the kiln and the building.  The first situation is under-supplied voltage: a 240-volt kiln firing on a 208-volt supply.  Because 240-volt kilns are quite common, this can be a problem at many schools if the power supply was not confirmed before the kiln was purchased.  In this scenario, the kiln will be constantly underpowered and struggle to reach high temps (cone 5-10).  It will be able to reach lowfire glaze and bisque temps (cone 06-04), but it will take longer than normal because the kiln is not receiving the full amount of voltage for which the elements were designed. 

The second scenario is far more dangerous than the first.  It involves a 208-volt kiln being fired on a 240-volt supply.  We see this more commonly if someone buys a used kiln from a school and installs it at home, or sometimes if a kiln is moved from one industrial location to another and the locations do not have matching power supplies.  Just because both locations are commercial does not mean they have the same power supply.  Don’t assume.  Always get it checked out in advance.  The problem in this scenario is that the kiln will be overpowered and that extra voltage will damage the kiln.  The 208-volt kiln is designed to run on 202-214 volts (+/- 3%).  When it receives 240 volts, that is a 15% overage, and that is enough to burn out the elements and damage the relays and even the computer controller. 

You can easily avoid all of these problems by confirming that the power supply at your location matches your kiln.  If there is a mismatch, often the easiest and least expensive way to correct the problem is to install a new set of the appropriate voltage elements.  The elements are the only difference between kilns wired for 208 volts and 240 volts*. 

*Please review the maximum firing temperature if you are converting the voltage of the kiln.  In some cases, the max temp will be reduced.  Additionally, please note that there are other wiring changes if you have a mismatch in phase (1 vs. 3) between your power supply and kiln.  Contact technical support for more information about either of these situations. 

You can use the Skutt Build-A-Spec tool (https://skutt.com/shop/build-a-spec/) to create a printable page to give to the electrician that will detail all of the important information for them to know about your kiln.

For instance, if the power supply at your home is single phase, 240 volts, and you chose the model KM-1027-3 kiln, then you would need to inform the electrician of the following requirements supplied by the Build-A-Spec tool:

  • 6 gauge COPPER wire (it is very important that it is copper and not aluminum)
  • NEMA 6-50 receptacle
  • 48-amp draw will require a minimum of a 50-amp circuit breaker (and in some cases 60)

 

Wiring Gauge

The gauge (thickness) of the wire is important so that it is sufficiently sized to handle the flow of electricity for the kiln.  If it is too small, the wire will get hot and could be a fire hazard.  There is no problem with the wire being over-sized, other than the added expense.  It is also important that the wire is made of copper and not aluminum.  Aluminum wires cost less than copper, but they have some distinct disadvantages.  Aluminum wires expand more than copper, they corrode, and they can’t handle as much amperage as a similarly sized copper wire.  Aluminum is a good conductor of electricity, but it is not as good as copper.  When electricity is flowing through an aluminum wire, the wire heats up a tiny bit.  When it heats up, it expands and then contracts when it cools.  This expanding and contracting movement has the effect of loosening wire connections over time.  Loose connections can come undone and become a fire hazard.  The connections can be re-tightened, but that requires additional maintenance and diligence to inspect those connections annually.  Aluminum wire also corrodes differently than copper when exposed to air.  Anywhere the insulation has been stripped off the aluminum wire, anti-oxidant coating should be applied, otherwise a white “rust” will develop.  This oxidation is not a good conductor of electricity.  It creates resistance and therefore heat, which is never a good thing in electrical wiring.  Copper, on the other hand, oxidizes very slowly but even that minimal oxidation is not detrimental because it is still a good conductor of electricity.  The final concern relates to the size of the wire (gauge).  Aluminum wires are not rated to carry the same number of amps as an equivalently sized copper wire.  From the example above, our KM-1027-3 kiln needs a 6-gauge wire because it draws 48 amps.  A 75°C, 6-gauge copper wire is rated for 65 amps, but a 75°C, 6-gauge aluminum wire is only rated for 50 amps.  The aluminum wire in this scenario would easily be maxed out, but the copper wire can handle the full load with ease.  To get the same amperage rating, the aluminum wire needs to be over-sized, which begins to negate the cost savings compared to copper, but you still have the other problems.  Stick with copper all the way. 

There are a few other circumstances that can affect which gauge wire needs to be installed at your location.  In all cases, any variation will be to install a thicker gauge wire than what is recommended, never thinner.  If the distance from your circuit breaker to the kiln is more than 50 feet, then you should typically install heavier gauge wiring (generally 2 sizes larger for every 50 feet of wire run) to minimize a low voltage condition to the kiln.  Additionally, using cable type circuit wiring (vs. individual wires in a conduit), or connecting to older type electrical equipment (60⁰C, vs. 75⁰C or 90⁰C), or installing in higher ambient temperature locations (hot attic) may require using a heavier gauge wire size.  Consult an electrician for your particular installation requirements. 

On a side note, if you are installing a smaller kiln but have reasonable intentions to install a larger kiln in the near future, it would be wise to consider installing larger gauge wire to begin with.  It will cost a little bit more, but you will not have to pull it out later on and run new wires if you want to install a larger kiln in the future.  A larger kiln may require a different sized circuit breaker and receptacle, but those can often be changed more easily than running new wires in the wall. 
 
Kiln receptacle style and location

Staying with our KM-1027-3 example, the Build-A-Spec tool lists a NEMA 6-50 receptacle.  This is the designation for what type of receptacle will match up with the plug on the end of the kiln’s power cord.  NEMA is the National Electrical Manufacturers Association, and they have designations for every plug and matching receptacle organized by maximum amperage ratings.  Skutt uses a limited number of plugs on the kilns we manufacture, but there are a variety of other plugs available for many other uses.  It is advised to not alter the original plug on your kiln, and, in some cases, it could void your kiln warranty. 

The installation location of your receptacle should be to the right of your kiln (from your perspective if you were facing the front of the kiln) and raised up about 18” off the floor.  The ground plug (round hole) on the receptacle should be at the top.  This orientation allows the power cord to hang down so that there is not any added stress on the connections when the kiln is plugged in. 

The kiln power cord is 6 feet long.  It is important that when the kiln is plugged in the power cord should not rest on the body of the kiln (it could get hot and melt) and should not be extended so far that the plug is stressed when inserted in the receptacle.   

If your kiln does not list a receptacle style, but instead indicates that your kiln is “direct wire” this means that the kiln is large enough and/or draws a significant amount of power that it cannot safely be plugged in conventionally.  The power cord from the kiln will be wired directly to a small box called a shut-off switch.  This box has an “on/off” lever that disconnects power to the kiln.  The box will be located on the wall where a traditional outlet would normally be installed.  The shut-off switch is then wired to the main circuit breaker panel in the same fashion as any other receptacle would be. 

Circuit Breaker

The final component that the electrician will need to install is a circuit breaker dedicated to your kiln.  The Build-A-Spec tool lists the maximum amperage draw for every kiln model.  The electrician can use that information to size the circuit breaker accordingly for your installation.  It is generally advised to have a circuit breaker that is 20% larger than the maximum draw that will be placed on it. 

Ideally, the circuit breaker panel should be visible from the kiln (located in the same room or very near by), so that power can be easily shut off to the kiln when needed.  If the circuit breaker panel is located far away in another part of the building, then the kiln should be direct wired to a shut-off switch. 

Additional Wiring Considerations

In addition to the special wiring just for your kiln, it will be useful to have access to a few standard 120-volt outlets near your kiln.  These are necessary if you will be installing an EnviroVent 2 kiln vent or just need to plug in an extra light or a box fan for room ventilation. 

 

In our next blog, we will review kiln room setup.

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cruise control

What is IR Comp and Why Should I Care?

The best analogy for IR Compensation is the Cruise Control on your car. When you want to keep your car speed at a specific MPH you set your cruise control. When you come to a hill your car needs more power to climb the hill so your Cruise Control gives it the right amount of gas to keep the speed constant while climbing the hill.

Most potters wheels have the same feature but it has a much less sexy name, IR Compensation. the “I” refers to current and the “R” refers to armature resistance. The adjustment is hidden in your wheels control box on the controller’s circuit board along with settings for speed control and torque. Manufacturers don’t like you messing with these settings because they are generally “tuned” to the size of your motor, pulley, belt… you get the picture.

So, to use the analogy: your wheel is the car, IR Comp. is the cruise control, Amperage is the fuel, the force you put on your wheel while throwing (especially centering) is the hill and the foot pedal is… well the foot pedal and the motor is the motor. Now I personally do not like using Cruise Control in a hilly area. That is primarily be-cause I have mostly owned small engine vehicles where I have to slam the gas pedal to the floor to get up hills and when I let cruise control try and do this it gets a little jolty (not sure if jolty is a word but I think you all know what I mean).

The bigger the engine (motor) and the smaller the hill (pressure on the wheel head), the less dramatic the joltyness (can I trademark that word?). A few more things come into play like the sophistication of the controller and the degree of IR Comp employed, but let’s get back to that later.

So, if I am driving an old VW Bug that needs a tune up and you are in a brand new 12 Cylinder engine Jaguar and we hit the same hill, I am going to slam my pedal to the floor boards while you barely have to move your foot. In other words, the adjustment is subtle because it is not putting much strain on your huge motor. This is probably why they never put cruise control on VW bugs. It would probably pop the seat right off the rails.

Okay, so what does this have to do with throwing pots? For most people, not much. For people throwing very large pots and for people throwing very thin, wide bowls at low speeds, it can be the difference between success and failure. Imagine you are dropping the walls on a 3 ft. diameter, razor thin, platter and the wheel gets a little unexpected jolt when the IR Comp kicks in.

Let’s face it, your foot pressure could be less smooth then the IR Comp so what is the solution? Buy the Jaguar with the 12 cylinder engine and never set your cruise control. In Skutt terms, get the wheel with the biggest motor you can afford and don’t worry about IR Comp because we never turn it on.

The founder of Thomas Stuart wheels, now Skutt Wheels, was a big pot potter. When he designed the wheels he specifically chose a motor that was strong enough to maintain a consistent wheel head speed, while the wheel was turning slowly, subjected to the resistance created by the weight of a lot of clay and without having to incorporate IR Comp.

So let’s get back to controllers. If you are not going to use IR Comp you are going to occasionally have to put your foot down on the gas to maintain wheel head speed. When you do this you want the power to be delivered as smoothly as possible. Think of the SSX Controller upgrade like replacing your carburetor with an electronically controlled fuel injector.

The SSX controller has more sophisticated and robust components. One of the most important of these components is it’s large capacitor. A capacitor stores energy much like a battery. Having this stored energy allows you to feather in the power when you needed it more precisely and therefor results in a smoother transition at low speeds.

For 99% of the potters out there, our 1/3 HP motor with the standard controller is perfectly satisfactory for their needs. Unless you are working with a wheel every day, making challenging pieces, you probably will not even notice the difference of any of these factors we just discussed. So, save your money for clay and just concentrate on whether you want a built-in splash pan or a removable splash pan. We will talk about that in future Blog Posts.

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hot keys

Ceramic Hot Keys

hotIf you own a Skutt Kiln with a KilnMaster Controller you may only be using a fraction of the features available to you. Some of the coolest features are accessed while the kiln is firing. We call these Hot Keys. Most of these give you diagnostic information that is helpful troubleshooting your kiln or just gain better insight into the actual performance during the firing. Below is a list of the Hot Keys and their functions on newer KilnMaster Controllers (ones with green display lights):

1, 2 and 3

Skutt Ceramic Kiln Hot KeysThese keys will display the temperature reading of the corresponding thermocouple on a Zone Control Kiln. Zone Control is an optional upgrade available that places a thermocouple in each section of the kiln. This allows the controller to sense when one section of the kiln is firing too hot or too cold and make adjustments during the firing.

In a 3 section kiln, the one key will display the temperature in the top section, 2 will display the middle, and 3 will display the bottom. The controller must be configured for Zone control for these keys to work.

5

The five key will display the programmed rate of rise in degrees per hour for the active segment in the program.

7

The seven key will perform an Amp check and then continue the firing. It will temporarily stop the program, turn each relay on individually and give you the amp reading. Once all the relays have been cycled on it will continue the firing. A list of the desired amp readings for each model can be found under the Library tab on the Skutt website under troubleshooting.

Each Amp reading represents a section of the kiln starting from the top. If your kiln only has two sections the 3 reading will be zero. If one of the sections that does exist comes back with a reading of Zero, chances are likely you have a relay out. If it is reading low, it may be an indication that your one or more of the elements in that section are starting to wear out. It is a little more complicated than that so if you want a complete description on how to accurately interpret the results read the white paper on Interpreting Diagnostics under the Library Tab of the website.

8

The eight key will flash 3 decimal points representing the outputs on the control board. The outputs are what tell the relays to turn on. The one on the left will represent the top section of the kiln, the middle represents the middle section and the one on the right represents the bottom section.

This is a very complex troubleshooting tool and almost always needs to be used in conjunction with other tests to gain useful information. Most likely this test will be initiated at the request of a Skutt Technician.

0

The zero key will tell you the elapsed time since the kiln was started. This can help you estimate when to be there for the ending of the program.

View

The View key will tell you what segment of a program the controller is currently running. It will also tell you what we call the “traveling set point” and the temperature of the circuit board. The traveling set point is the temperature where the kiln is supposed to be if it were keeping up with the program.

Just because you program a kiln to fire at a particular rate to a temperature does not necessarily mean it is capable of achieving that rate. It will only do the best it can. This diagnostic feature allows you to see the actual performance. Again this feature requires advanced troubleshooting skills to extract meaningful data and will most likely be interpreted by a Skutt Technician.

The Board Temperature is a very useful in determining if your kiln room is properly ventilated. It’s kind of hard to believe that the room temperature could have much impact on the temperature of the circuit board when it is sitting so close to a kiln chamber that is 2350F, but it does.

If the board temperature reaches 160F the kiln will shutoff to avoid damaging the controller. We calculate that if the room air exceeds 100F while the kiln is firing you run the risk of getting an “E-bd” error and the kiln shutting off. Often times a fan blowing on the controller is enough to prevent this from occurring.

One last feature accessed through the view key is “skip step”. This will advance any program to the next segment in the program. To activate skip step press View then ENTER and ENTER again.

Review

Review is generally used prior to pressing Start to ensure you have entered the correct program but it can also be pressed while the kiln is firing just in case you are second guessing yourself (or someone else who may have programed the kiln).

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elements

Top 5 Ways to Extend the Life of your Kiln Elements

elements Let’s face it, elements are expensive and there are plenty of things you would rather be doing on a Saturday than spending an afternoon replacing them. Unfortunately, just like the brakes on your car, you are eventually going to have to replace them. The good news is that, also just like brakes, there are a number of things you can do to extend their life. In order to better understand why we recommend certain practices it is helpful to know a little something about how elements age.

The most widely used element wire is Kanthal A-1. It is composed primarily of Iron, Cromium and Aluminum. Element life is determined by the rate at which the Aluminum oxidizes. The hotter the element temperature, the faster it oxidizes. The amount of time you spend at high temperatures (ex: slow cooling Cone 6 glazes) compounds the problem.

Whether it is a new kiln, or you have just installed new replacement elements, the first firing is critical. You will notice new elements are bright and shiny. The outside surface of the element begins to oxidize when it reaches 1832 F. The temperature of the kiln could be significantly less. The degree of temperature difference will depend on the element design, the rate at which you are firing and a number of other factors. As the element oxidizes it forms an aluminum-oxide layer around the core. The goal is to form a uniform, dense oxide layer that is well bonded to the base metal. We have found a Medium Speed, Cone 04 ConeFire program does a very good job of achieving this.

ELEMENTDEGRADATION-GRAPHICWeb

This oxide layer prevents the further oxidation of the alloy base metals by providing a barrier that resists the diffusion of oxygen into to the alloy and also prevents the diffusion of metal ions to the alloy surface. The first time you fire the element it is basically naked with nothing to protect it. If you fire the kiln empty with nothing to release damaging gases, it helps the element form a nice uniform oxide coating with minimal initial damage to the metal.

As you continue to heat and cool your kiln the element continues to expand and contract. Every time it expands and contracts, tension is formed between the the oxide coating and the base metal because they expand at slightly different rates. This forms little fissures in the oxide layer which expose the core. The exposed core then oxidizes and fill the fissures with new aluminum oxide. This both elongates the element and reduces it’s diameter.

As the core gets smaller and smaller, the resistance of the wire increases causing the element to run hotter thus compounding the problem.The net effect is a reduction in the power potential of the element.

As the element gets longer and thinner, the distance between coils becomes less. This is what is called element creep. When the distance between coil turns becomes less, the element gets hotter because the coil turns are radiating more heat on to each other. Remember that hotter is bad so this also compounds the problem.

A well designed element will ideally have the largest diameter (more core material to fill the cracks) and the largest distance between the coils (runs cooler). The heavier gauge elements also have more dimensional stability. When elements get above 1700 F they start turning into the consistency of cooked spaghetti. As they soften, the coils want to start laying down, causing the distance between the coil turns to lessen. Therefore, the thicker they are, the better they can support themselves at higher temperatures. Because of this you can also increase the distance between the coils (increase the pitch).

Okay, now that we know how elements degrade, lets look at what we can do to slow the process.

1. Choose the Right Kiln for the Job

Every kiln has a maximum temperature rating listed on the serial plate. It is the maximum temperature a kiln can achieve under “normal” conditions. This is a lot like the maximum load capacity for a pick-up truck. Just because a 1/2 ton truck is capable of hauling a bed full of gravel, it does not mean it is the best choice if you are a contractor who hauls gravel everyday, up hill, low on transmission fluid, in the Mojave Desert… you get the point. Things always last longer when you do not push them to their limits. A good example of this are 10 cu/ft kilns.

Kilns like the KM1227-3 are designed to use a common sized 50 amp plug. Manufacturers need to limit the amperage of this size model to accomodate the plug, therefore they cannot put the power into the design that they would prefer. At Skutt we offer the “PK” version of these size kilns for those people who are not restricted by this plug requirement. This would be a much better choice for artists that are consistently wanting to fire their kilns at high temperatures. One of the biggest reasons why elements last longer in more powerful kilns is because they can reach temperature faster and are not spending unnecessary time at high temperatures. If you are consistently firing to cone 6, you will be much happier with a kiln rated to cone 10

Ideally everyone would use low fire ceramics. In reality, there are a lot of characteristics (i.e crystal glazes) and properties (i.e. freeze resistant tile) that are impossible to achieve at low fire temperatures.

Cup Head System Skutt Potters Wheels

2. Keep Your Elements Clean

Road or rail vibration during shipping can cause brick dust to become airborne and settle on the elements. When you fire your kiln for he first time this dust can interfere with the creation of a good oxidation coating on the elements. It can also cause the element to run hotter as it restricts heat from escaping and burns off any combustibles. This also happens over time with just normal use. As the elements expand and contract they can loosen brick material that settle on the elements. In addition the normal dust associated with a clay studio can settle on the elements when the kiln is being loaded and unloaded. Occasionally bits of clay and glaze can fall into the element groove. These are extremely important to remove since they have the potential to completely burn through the element.

A good rule of thumb is to vacuum out your element grooves at least one a month and always vacuum out the kiln before it is fired with new elements.

3. Fire New Elements With the Kiln Empty

Just as dust is bad for the creation of a good oxide coating, so are the fumes that can emit from clay and glazes. Therefore, make sure your first firing with new elements is with the kiln chamber empty. As mentioned earlier, run a Cone 04, Medium Speed ConeFire program for best results.

4. Vent! Vent! Vent!

Even if you have the best oxide coating ever, the fumes that emit from clay and glazes can still attack the element when it expands through heating and forms cracks in the coating. Downdraft vents are your best defense against potentially harmful fumes. Downdraft vents pull the fumes from the kiln chamber before they have a chance to damage the elements. If you do not have a downdraft vent your next best option is to prop the lid a couple of inches until the kiln reaches 1000 F to allow the fumes a path to flow out of the chamber. You should also leave the top peephole out during the entire firing to handle those fumes that escape above 1000 F. Trying to reduce in your kiln will clobber their useful life and is definitely not recommended.

5. Keep the Elements Supported

We mentioned earlier that elements soften when the are heated above 1700 F (again this is the temperature of the element not the kiln chamber) and can actually droop out of a broken element groove and eventually break from elongation. Eventually this brick should be replaced but if you do not have the time you can help things by creating a little fence to hold the element in place using element pins. Usually a good time to replace brick is when it is time to replace your elements.

By following these guide lines you can easily double the life of your elements. In future blogs we will discuss the benefits of APM elements. Until then, be safe, creative and happy!

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