What type of relay utilizes a heater coil to melt a eutectic alloy?

The melting alloy overload relay is designed specifically to use a heater coil to melt a eutectic alloy. In this type of relay, the heater generates heat that causes the eutectic alloy to melt at a specific temperature. When the alloy melts, it loses its structural integrity, causing a mechanism to trip and interrupt the circuit, thus providing overload protection.

This method is particularly effective in providing a clear and reliable overload indication, as the melting point of the eutectic alloy can be precisely controlled to match the desired overload conditions. Therefore, the use of a eutectic alloy is central to the operation of the melting alloy overload relay, making it uniquely suited for this kind of thermal protection application.

Other types of relays, such as electromagnetic overload relays and thermal overload relays, typically operate on different principles that may not involve the melting of an alloy. Bimetallic strip relays rely on the differential expansion of two metals to cause bending and tripping, rather than melting materials.