(or, how to speak “electrician”)
This is intended to be a guide for selecting a kiln and to understand the power available at your location. It is not to be taken as an authoritative or definitive document. If you have any concerns or questions about the circuits in your location, please consult a qualified electrician and your local electrical codes before playing with the electricity.
Within this document:
- General information about electricity
- General information about kilns and electrical requirements
- Ordering a kiln for your current location
- Ensuring a proper electrical fit when you have purchased a used kiln, or have moved your current kiln to a new location
- Some things to consider/know/have awareness about
- Proper Electrical Kiln location for electrical considerations
Very helpful link: Great Lakes Clay “How to buy a kiln” greatclay.com
Fraser, Harry. The Electric Kiln: A Users Manual (Ceramics Handbooks). Philadelphia, PA: University of Pennsylvania Press, 2000.
Ritchie, Ralph W. Electric Kiln Handbook. 2nd ed. Springfield, OR: Ritchie Unlimited Publications, 1996.
1. General information about electricity
Here are some simple definitions to better understand electricity.
Volt (V)-A unit of measurement that tells you the electric potential, electric power is under pressure, and this pressure is measured in volts.
Amperes (A)-The measure of current, which is the rate or strength of electrical flow.
When amps and volts are considered together they describe power flowing, which is the watts. volts x amps = watts
Watt (W)-A unit of activity or power corresponding to the rate of work represented by a current of one amp under a pressure of one volt.
Electric power is measured in kilowatts,1 kilowatt=1000 watts.
Resistance (R)-Degree of resistance to the passage of current is measured in ohms (Ω).Here is an analogy to explain volts, amperage and resistance: If there is a pipe full of marbles, the force used to push the marbles through the pipe is what electricians refer to as volts. The number of marbles counted in a cross section of the pipe is what electricians refer to as amperage. The friction inside the pipe that causes the marbles to flow slower is what electricians refer to as resistance, which is measured in ohms.Single phase vs. 3 phase
The number of phases relates to how many wires come from the power company into your location. In general, single phase is in residential applications, while three phase is in commercial / industrial applications.
Single Phase 110V: There are three wires, one has power, one is neutral and one is the ground.
Single Phase 220V four wire: If your kiln cord plug has four prongs, you have a four wire kiln. Two of these wires are for power (red, black), one wire is neutral (white), the last wire is ground (green). This arrangement allows the kiln to use either 220 volts or 110 volts to the kiln elements. Single Phase 208V four wire : This uses only two powered wires of the 208V three phase circuit and the ground. These show up in schools that have three phase panels.
Single Phase 220V 3 wires: If your kiln cord plug has three prongs, you have a three wire kiln. Two of these wires are for power (red, black), one wire is ground (green) and there is no neutral wire.
Generally three phase power is found in commercial / industrial buildings. It would be uncommon for traditional studio potter kilns to be three phase. It would be common for larger scale commercial / industrial kilns to be three phase.
Three Phase 208V : There are typically four wires. One is ground (green) the others have power (red, black, blue).
A single phase kiln will run on both three phase and single phase power supply, however, without a transformer a three phase supply will only provide 208 volts, not 240. A 240 single phase kiln can usually be run on 208 single phase. Running a 208 single phase kiln on 240 usually requires new elements. You should consult the manufacturer.
2. General information about kilns and electrical requirements
Voltage requirements for kilns
240 volts: 220 V, 230 V and 240 V these are in all practicality the same thing. Some people will call it 220v and some will call it 240v, etc. Virtually all US households have this power available, it is commonly used for electric dryers and kitchen stoves/ovens. Depending on the time of year, voltage supplied to any one area can fluctuate up or down, which could effect the length of firing of your kiln.
Before installing a new outlet for a kiln consider the largest amperage that you may ever want at that location. Also consult a kiln manufacuterer’s literature. They often specify a larger wire size than the default size suggested by electricians.
In your electrical panel you need the designated circuit breaker to be 20-25% greater than the amperage required on the kiln. This is a code issue, and you need to research this percentage – ask your licensed electrician.
208 volts: 208 V is different than 110v and 240v. It is most often found in schools, industrial settings or residences where industrial power is available. A 240v kiln can be fired in a 208v supply, however, it will take longer because the supply has less power. Most kilns can be ordered in 208v instead of of 240v if this is what your supply requires. A kiln equipped with 208 volt elements is not as forgiving when applied with 240 volt power source (element life may be shortened).
120 volts: A quick note about 120 volt kilns. Residences with 240 volt service and schools or businesses with 208 volt service all can accommodate kilns firing at 120 volts. Some test kilns, generally with only one element, run on 120v.
Amperage requirements for kilns
This will be expressly stated in the literature about the kiln, and on the kiln itself. (If there is not a plaque near the electrical components, when the kiln is unplugged, open the protective cage around the electrical panel and look inside). On older kilns, you may have to locate a kiln identification number and call the manufacturer to obtain the information.
In your electrical panel you need the designated circuit breaker to be 20-25% greater than the amperage required on the kiln.
Generally kilns that draw more than 48 amps do not come with plugs; they must be wired directly into your power supply.
3. Ordering a kiln for your current location
The three things that you need to know when ordering a kiln are available voltage, available amperage, and whether you have single or three phase capability. Your electrician can answer all of these questions. A service call should cost around $50 dollars (depending on your location). Call and get some price quotes, some electricians will deduct the fee for the service call from any future work that the installation will require.Available Voltage
Consult your electrician to determine the voltage at your location.
There generally are two voltage services available; 240 volt and 208 volt. If the kiln is to be used in a home, it will likely use 240 volts. This is the service provided to private residences by the electric company. Schools and industrial buildings usually are supplied with 208 volt service. Both voltage systems use the same wall outlets, so you can’t tell voltage by the type of outlet.
Test kilns: Most 110 electric outlets are meant for less than 15 amps. Some test kilns draw near 20 amps. For these a special dedicated outlet should be installed. There can be no other devices on the circuit.
Consult your electrician to determine the available amperage at your location. Make sure that the total amount of amperage available is enough to run all of the equipment and fixtures, (including your new kiln) you will be using. Increasing the amperage supply to your building can be very expensive. When purchasing a kiln, make sure you are not going to exceed the available amperage.Single or Three phase
Consult your electrician to determine what type is available for your location. General rule of thumb, residential is single phase and commercial is three phase.
If a building is equipped with single phase service, the kiln must be wired for single phase. However, with buildings supplied with three phase power you can choose between a single or a three phase kiln.
In general there are no advantages to buying a three phase kiln to elements or your firing. If you are purchasing a three phase kiln, please research why this is a better choice for you.
4. Ensuring a proper electrical fit when you have purchased a used kiln, or have moved your current kiln to a new location.
Similar to ordering a new kiln, the three considerations are volts, amperes and single or three phase.
However, rather than having a kiln built to specifications, all of the variables are determined by your location and the kiln in your possession. You need to establish if the electrical supply will complement the electrical requirements of your kiln, and if not, what will remedy the situation.
- There should be a plaque on the exterior of the kiln’s electrical panel (near the switches), which indicates the power requirements of that specific kiln.
- Your electrician will be able to tell you if your location supplies what you need for that specific kiln.
5. Some things to consider/know/have awareness about
- A 240 single phase kiln can usually be run on 208 single phase. Running a 208 single phase kiln on 240 usually requires new elements. You should consult the manufacturer.
- A three phase kiln will only run on a three phase power supply.
- The kiln will not function properly if the volt and amperes requirements are not met.
- If you run a 208 volt kiln at 240 volts you will wear out your elements much faster than if you run it at 208 volts.
- Your circuit breaker/fuse must be rated to your kiln, both with the amperes and the volts.
- The volts should match
- The amps of the circuit breaker should be rated 10-15% higher than the requirement. For example a 240 volt kiln that requires 48 amps will need a 240 v circuit breaker rated to 60 Amps. 15% of 48 is 7.2, and 48+7.2 is 55.2. The next available amperage circuit breaker is 60 amps. Therefore the switch necessary for that kiln is a 240v/60 amp circuit breaker.
- The element wire in the kiln needs to be a correct fit with the voltage and amperage available. Therefore, it is important to know your available voltage, amperage and ohms of the coils. With a used kiln, you may need to determine the resistance of the coils if your kiln is not working properly.
- If you kiln has a plug attached at the end of the wire (rather than requiring hard wiring to the electrical box), make sure that the plug’s electrical rating matches the electric kilns requirement. Also make sure that the wall outlet and wiring in the wall matches the electric kilns requirements. Unless you know a lot about electricity, electricians are required to determine this information.
6. Proper Electric Kiln location for electrical considerations
- When choosing a location for your kilns try and stay within a 50 ft wire run from your breaker box. If it is necessary to run the power farther then 50 ft you will need to increase the wire gauge to the breaker box.
Resources for information
- Wikey,M. Calibrating & Calculating the electric kiln. San Jose: Marshall Craft, 1979.
- Skutt, Kilnselection.pdf available online at skutt.com
- L&L Kiln Mfg Inc, element.pdf, available online at hotkilns.com
- L&L Kiln Mfg Inc, electric kiln volts.pdf, available online at hotkilns.com
7. Solar Electric Kilns
“Some occasional ramblings about solar power with regular statistics on energy produced by a system in Canterbury UK.”
This is a blog from the UK about firing electric kilns with solar power: