Commercial heat treating ovens and kilns are typically powered by either electricity or gas. For our purposes, in this article, we’ll only be discussing electric power requirements. The larger the firing chamber in a kiln, the greater amount of power will be required to operate the unit. We know that volume of space to heat translates to increased power demand. So, before you make a decision to about which industrial kiln or oven to purchase, you must first consider the possible location and the available power source location for your unit. As a rule, small kilns (under 15") can operate using standard 120 volt power. Larger kilns typically require 240 volts to operate. In some settings 208 volts or 480v may be all that is available. Here’s a look at the options.
120 Volt Kilns
Smaller kilns (under 13”) typically run on 120 volt, 13 amp current. This will allow the owner to plug the kiln into just about any standard plug. Most standard household or light office environment breakers are 15-20 amps, so a 13 amp draw on that breaker will not overtax or “blow” the breaker. As the firing chamber increases in size (14” – 18”) the amperage required to heat the chamber will increase to 15-17 amps. These higher amperage requirements will dictate the need to install a dedicated circuit of 20 amps to be installed. This new circuit will be dedicated specifically to the kiln, and will not have anything else attached to it that will draw power. A licensed electrician should install a dedicated circuit, and will typically do that for a nominal fee. See this great article on the difference between a dedicated 120v circuit and a standard 120v circuit.
240 Volt Kilns
Larger kilns (over 18”) typically operate on 240 volts and may require either 30, 40, 50 amp service, these units will come with factory supplied cords and plugs. Higher than 50 amps requires the unit to be direct wired, so the unit will come with a cordset only and no plug. These kilns usually require the services of a licensed electrician for installation of special receptacles and special wiring. According to one manufacturer, incorrect voltage is the number one mistake made by customers when ordering a kiln. Be sure that you know whether the available the service is 208 or 240 volts, as the wiring looks exactly alike. Standard electric kilns will run on 240 volts, single phase.
208 Volt Kilns
208 volts is most often found in schools, industrial settings or occasionally residences where industrial power is available (converted industrial areas). Most kilns can be ordered in 208V versions, but sometimes have different maximum firing temperatures because of it. Check the specifications, or if your are interested in one ask a representative. 208V is created by using 2 legs of a 3 phase circuit, 120 degrees out of phase.
If a 240-volt kiln is operated on 208 volts it will lose 25% of its power. Even if that is ok for you, the kiln will work harder to do its job and the components will wear at a faster rate. If a 208-volt kiln runs on 240 volts it will exceed the ratings of the kiln and will most likely trip your circuit breaker. Both 240V and 208V kilns can be wired as 3-phase if required.
480 Volt Kilns
480V 3 phase is an electrical power typically used in industrial and commercial settings. It is a high voltage system that can provide a lot of power to run large machinery or equipment. 480V is the voltage between phases of a 3-phase “Y” circuit that's 277V from hot to neutral. In keeping with 110V versus 120V strangeness, motors intended to run on 480V three phase are often labeled as 440V. Both 460 V and 480 V are three-phase voltages used for supplying industrial loads. Domestic systems, having lower power demands, operate with lower voltage levels. Residential utilization voltages in the USA are 110/115 V and 220/230 V for single-phase and three-phase, respectively.
In a 3-Phase Supply system, the lower voltage (typically 277V or 347V) will be the 'Line to Neutral Voltage' which is the measured voltage between one of the three lines and the neutral. The higher voltage (typically 480V or 600V) will be the 'Line to Line Voltage.'
Can households receive 480 volt? Typically no, for one simple reason. It's not used in residential areas, so there won't be any service available. It's also not suitable for residential areas and no utility would allow it to be delivered. Precaution is necessary for such voltage amount and how dangerous it could be. Reference: Electrical Technology.Org, Standard Electrical Voltage Levels in the US
Direct Wire
All kilns drawing over 48 amps are direct wired. 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.
The final component that the electrician will need to install is a circuit breaker dedicated to your kiln. 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. 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.
Final Thoughts
Another issue to consider is distance from the power source. Always test your wiring with a multimeter to ensure that you actually have the voltage and flowing through the line that you think you have. Just because you are supposed to have the power, doesn't mean you actually have it. The further away you get from your power source the more drag there is on the power and the less voltage makes it to the end of the line. In industrial settings this could be how far the unit is from the incoming transformer or the breaker box for the building. In light industrial settings it could be as simple as being the last building at the end of a row of other buildings that are drawing electrical as well. Until you need to draw a large amount of power you never know if your "pipe" is insufficient. Always take a reading so you know what you are dealing with and then you can address how to augment your power needs, or reposition the unit into a place where more power is available. You might even consider switching to a gas unit if you have that option. We will cover that in our next article.
To provide the performance the kiln was designed to give, it must have the proper outlet and matching breaker to supply adequate voltage and amperage. An incorrect connection may cause disappointing or even hazardous results. If you have questions, we always recommend talking to a licensed electrician.
As always, feel free to reach out to our experienced team with questions or comments. We're always here to help! Give our technical team a call at (210) 446-9979 or email us at customerservice@heattreatnow.com