Square D A.78 Contactor Thermal Unit

Product Description

The SQUARE D A.78 is a thermal unit designed as an accessory for contactor and overload relay assemblies used in motor control and HVAC electrical systems. Thermal units serve as the sensing element inside overload relays, calibrating the relay to trip at the correct current threshold for a specific motor load. This unit measures 2.4 inches in length, 1.2 inches in width, and 0.8 inches in height, and weighs 0.04 pounds. It is installed by licensed electricians and HVAC controls technicians performing motor protection work on commercial and residential equipment.

Thermal units like the A.78 are used in motor starter and contactor assemblies where overload protection is required. Typical applications include electric motor circuits in HVAC equipment such as compressors, air handlers, and pumps. The correct thermal unit selection is based on the full-load ampere rating of the motor being protected, so verify the motor nameplate data before selecting a replacement unit.

Key Features

• Designed as a replacement thermal unit for compatible Square D overload relay assemblies
• Compact form factor: 2.4 inches long, 1.2 inches wide, 0.8 inches tall
• Lightweight at 0.04 pounds for easy handling during installation
• Single-piece package quantity suitable for individual relay replacement
• Functions as the trip-sensing element to protect motors from sustained overload current

Compatibility

Designed as an OEM-style replacement thermal unit for compatible Square D contactor and overload relay assemblies. Verify the specific overload relay model and required thermal unit class before installation.

Installation Notes

Installation should be performed by a qualified electrician or controls technician in accordance with NEC guidelines. De-energize and lock out the panel or motor control center before removing or installing any thermal unit. Thermal units must be matched to the motor full-load ampere rating as specified by the overload relay manufacturer. Do not mix thermal unit classes or ratings within a multi-pole overload relay assembly.