Square D 9999ST1 Transient Suppressor Type S Contactor

Product Description

The SQUARE D 9999ST1 is a transient suppressor designed for use with Type S contactors in motor starter assemblies. Transient suppressors absorb voltage spikes and electrical noise that occur when inductive loads switch on and off, protecting control circuits and extending the service life of contactors and associated components. The 9999ST1 measures 4.5 inches in length, 3.1 inches in width, and 1.5 inches in height, and weighs 0.2 pounds. Electricians and industrial maintenance technicians install this accessory as part of a motor control center or standalone starter enclosure build or repair.

This transient suppressor is a direct accessory for Type S contactors in the SQUARE D starter lineup. It is suited for commercial and light industrial motor control applications where inductive load switching generates harmful voltage transients on control wiring. Typical installations include HVAC compressor starters, pump motor controllers, and conveyor drive panels where protecting low-voltage control circuits from spike damage is a maintenance priority.

Key Features

• Designed specifically for Type S contactors as a factory-matched starter accessory
• Absorbs voltage transients generated by inductive load switching to protect control circuits
• Compact form factor at 4.5 x 3.1 x 1.5 inches for easy integration into existing enclosures
• Lightweight at 0.2 pounds for straightforward field installation
• Single-unit packaging supports one-at-a-time replacement or new-build installations

Compatibility

Designed for use with SQUARE D Type S contactors as a direct starter accessory. Verify contactor series and frame size against the 9999ST1 accessory catalog before installation.

Installation Notes

Installation should be performed by a licensed electrician in accordance with NEC requirements and the applicable equipment manufacturer instructions. De-energize and lock out the motor control panel before removing or installing any starter accessory. Confirm the transient suppressor terminals are fully seated on the contactor before restoring power. Do not install on energized equipment.