Agilent Technologies 59510A and 59511A are relay devices designed for control from 66xxA and 603xA power supplies. These power supply accessories can be configured to switch dc power to multiple test fixtures, or can be used to provide an extra measure of protection in the case of a fault condition where emergency shutdown is required. The 59511A has all the features of the 59510A, and also provides relays for polarity reversal. Each box switches one power supply output. They can be used with any dc power supply which falls within the voltage and current limits. The internal microprocessor sequences the switching of power and sense leads. This protects the load by minimizing possible voltage overshoots. When used with Agilent system power supplies that have been configured appropriately, the relays can be controlled through the power supply GPIB port. For other applications, the 59510A and 59511A are controlled through a TTL port. Both relay accessory models can be mounted on any one of three sides to a flat surface with the PEM fasteners provided. The Rack Mount Kit (Option 850) eases mounting behind the power supply or towards the front of the equipment rack.