When firing a kiln, it’s not uncommon for the plug and socket to become hot. This document explains why that happens and what can be done to prevent it.
Kilns rated at 2.9kW to 3kW (regardless of manufacturer) operate near the upper limit of a standard 13 amp plug. To function properly, they must draw close to the maximum 12.5 amps. Drawing less current can result in slow heating or failure to reach the desired temperature. Drawing more can exceed the safe limit, risking overheating. This issue isn’t unique to kilns; other appliances like 3kW oil-filled radiators and convection heaters behave similarly. The key difference is duration; kilns often run for several hours.
Electricity suppliers are permitted a voltage fluctuation range of -6% to +10%, meaning supply can vary from 216.2V to 253V. At the lower end, a kiln may only draw 11 amps or less, causing it to struggle and generate heat in the plug. At the upper end, 253V can result in a current draw of 14 amps, which is problematic.
Most users operate within the 230V–240V range. However, even within this range, heat can build up if the plug and socket connection is poor due to age, low-quality materials*, or internal faults.
Recommended Actions:
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Initial Monitoring: During your first few firings, monitor the plug and socket. The plug top should feel warm or neutral, not hot. If it becomes hot, action is needed.
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Consult an Electrician: A qualified electrician should assess the plug and socket while the kiln is operating. They may recommend installing a dedicated, switched spur supply.
Voltage Testing:
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If voltage exceeds 240V, consider upgrading to a 16 amp switched spur and wiring the kiln directly. Some kiln manufacturers may also suggest changing the heating elements to suit higher voltage.
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If voltage is around 230V or lower, replacing the socket face may help improve contact with the plug pins. This issue can affect even new sockets, though older ones are more prone.
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For voltages near 220V or below, some manufacturers recommend changing the elements to increase power and reduce firing time.
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Plug Replacement: If the socket is new and voltage is stable around 230V but heat persists, replace the plug. If under warranty, a new plug and lead may be provided free of charge.
Additional Factors:
Other conditions that may contribute to overheating include:
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Long firing ramps and climbs
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Overloaded kilns
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Worn or struggling elements
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Poor ventilation
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Damaged lid seals or kiln structure
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Running full-power programs during peak demand
Ultimately, replacing the socket with a 16-amp switched, fused spur is the most reliable solution.
*Cheap sockets often lack precious metal lubricants that reduce electrical resistance, corrosion, friction, and wear.
