Generally speaking, if you are in a residential setting your electrical service will be 240 volts. Industrial building and schools are usually wired for 208 volt service. Your kiln should be matched to the correct voltage.
Most electric kilns are wired for 240 volt or 208 volt power systems. Test kilns may be wired for 120 volts; if so, they will be compatible to either 208 volt or 240 volt system.
Electric kiln heating elements are rated for either 240 or 208 volts. Too much fluctuation (as in power reduction of your electrical service during peak usage hours) adversely effects the kiln's ability to reach temperature and also shortens the life of the heating elements.
Phase refers to the type of wiring used in your building. Single phase means that the power coming into the main circuit box is supplied through two 120 volt hot leads, plus a neutral lead and a ground. Homes are usually built with single phase wiring.
Most schools and industrial buildings are built with three phase wiring. Three phase 240 volt wiring consists of two 120 volt hot leads, one 240 volt hot lead, and a ground. Three phase 208 volt wiring consists of three 120 volt leads and a ground.
A building that has single phase wiring cannot accommodate a three phase kiln. However, the reverse is not true. A three phase system can safely be used for a kiln that is either wired for single or three phase.
Amperage, as well as voltage, must be taken into account. Homes are usually wired with 100 amp service. This amperage is divided between the areas attached to the main power box, as can be seen in the amperage rating for each breaker or fuse in your power box.
Be certain that the circuit breaker or fuse for the outlet your kiln will use is more than sufficient for the kiln's needs. Bear in mind that the kiln's power draw will fluctuate during firing. For example, a kiln rated to draw 48 amps should be on a circuit that provides 60 amps.
If the kiln requires more amperage than is available, amperage must be added to the current service or an additional power line with separate circuit box must be installed for the studio.
Electricity is nothing to take chances with. The above is meant to help you be an informed consumer; however, you should always consult with a licensed electrician.
Begin talking with your electrician prior to shopping for a kiln. Have them test your service and tell you what your system can bear in terms of voltage and amperage. Find out from them whether your building is single or three phase wiring. Talk with them about where you want to place the kiln, and how that will effect the kiln's power supply.
Potters tend to be do-it-yourself types of people. Fight that urge; this is definitely one time not to do it yourself. Have your electric kiln installed by a licensed electrician.