Solder pot open contactsīoth the bimetallic strip and melting solder-pot rely on thermal energy to trip their elements. This causes the line contacts to trip open and interrupt current flow to the motor. If an overload current is sensed by the heater elements for too long a time, then the alloy becomes a liquid, allowing the spring to push open the normally closed contacts. Different levels of tin and zinc in the solder change the melting temperature, allowing for use at many different current ratings and ambient temperature settings. The wheel is held in place by the solder inside the solder-pot assembly. If the wheel is allowed to spin, then the spring will push upwards and open the set of normally closed contacts. The melting solder pot consists of a heater element, a solder-pot assembly, ratchet wheel, and a set of normally closed contacts.Ī spring is held under tension by the ratchet wheel. Melting Solder Pot Solder pot closed contacts The heat source has caused the grey-shaded metal (the piece on the bottom) to expand faster than the blue-shaded metal (the piece on the top) and so has opened the set of normally closed contacts, thus interrupting the current flow to the motor. Here the normally closed contacts are allowing current to pass through them, while the heat source is beginning to deform the metal. Bimetallic contact in a normally closed position When an overload occurs, the bending action opens the set of normally closed contacts, interrupting the current to the circuit. When used in an overload device, the bimetallic strip is mechanically linked to a set of normally closed electrical contacts. This bending action can open or close a set of contacts. As they heat, they expand at different rates, which causes them to bend or deform at a preset temperature. The bimetallic strip consists of two dissimilar metals with different heating coefficients. The types of relays most commonly seen are the bimetallic strip and the melting-solder pot assembly.
#Audio overload manual series
A set of normally closed contacts that are connected in series with either the lines feeding the motor (manual starters) or the coil of the magnetic contactor (magnetic starters).All current drawn by the motor must pass through the heater element. A heater element that is connected in series with the power line to the motor.Motor Starters and Contactors 12 Overload RelaysĬlick play on the following audio player to listen along as you read this section.
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