Square D A4.79 Thermal Unit Contactor Accessory

Product Description

The SQUARE D A4.79 is a thermal unit designed as an accessory for use with compatible contactors and motor starters. Thermal units serve as the sensing element inside overload relays, responding to heat generated by excess current draw to trip the relay and protect motors from damage. This part is a direct replacement component installed by licensed electricians and industrial maintenance technicians during overload relay service or motor protection system upgrades. It measures 2.4 inches in length, 1.2 inches in width, and 0.8 inches in height, and weighs 0.04 pounds.

Thermal units are used in commercial and industrial electrical systems wherever motor overload protection is required. Common applications include HVAC compressor circuits, pump motor controls, conveyor systems, and other motor-driven equipment where overload relays are part of the control panel or motor control center. Installation typically involves replacing a worn or incorrectly rated thermal unit inside an existing overload relay body mounted in a panel or starter assembly.

Key Features

• Functions as the current-sensing element inside compatible overload relays
• Compact form factor: 2.4 inches long, 1.2 inches wide, 0.8 inches tall
• Lightweight at 0.04 pounds for easy handling during panel work
• Sold as a single unit for targeted replacement without excess stock
• Designed as a contactor accessory replacement component

Compatibility

Designed as an OEM-style replacement thermal unit for compatible SQUARE D overload relays and motor starters. Consult the overload relay documentation or motor starter sizing chart to confirm the correct thermal unit selection for the specific full-load amperage of the motor being protected.

Installation Notes

Installation should be performed by a licensed electrician in accordance with the National Electrical Code (NEC). Always de-energize and lockout/tagout the panel or motor starter before removing or installing any thermal unit. The thermal unit slides or snaps into the overload relay body; verify the replacement unit matches the required trip class and amperage rating before reinstalling the overload relay cover. Never energize the circuit without confirming the correct thermal unit is seated properly.