Thermal overload relay is a bimetallic device made up of two strips of different metals. The dissimilar metals in these thermal overload relays are permanently joined. Heating the bimetallic strip causes it to bend because the dissimilar metals expand and contract at different rates. The thermal bimetallic overload relay strips applies tension to a spring on a contact. If heat begins to rise, the strip bends and the spring pulls the contacts apart, breaking the circuit.
Important performance characteristics to consider when searching for thermal bimetallic overload relays include full current load range, trip class, and temperature trip range. The adjustable current value allows the thermal overload relays to be set to the full-load current shown on the motor rating plate. This is the current range of the thermal component that can be adjusted to the desired trip point. The trip class is the maximum time in seconds at which the thermal overload relays will trip when the carrying current is at 600% of its current rating. Other important specifications to consider when searching for thermal overload relays include motor load phase, motor voltage, control circuit voltage, contact or output ratings, pole specifications, features, and environmental operating parameters. The motor load phase can be single-phase protection or three-phase protection.
Salient Features of SKYU Thermal Overload Relays:
- The triple pole bimetallic thermal overload relay is of the hand-reset type. It unmistakably indicates overload.
- A temperature compensation device prevents the relay from being affected by variation in ambient temperature.
- The entire relay unit is housed in highly voltage tasted Bakelite enclosure and is accurately calibrated and individually tested on an automatic test bench.
- Setting can be adjusted by means of a pointer.
- Satisfactory operation at all ambient temperatures from -5 deg.C to 55 Deg. C. SL1, SL2, SL3, SL-4, SL-6, SL-10, SL-12 relays are manual reset type.
- These relays are provided with auxiliary contacts having various thermal capacity
- These relays are suitable for direct mounting on Type SL contactors. 16 Amps to 300 Amps.