Emergency Power Off (EPO) Option for Galaxy Series UPS Systems


This application note will describe the EPO (Emergency Power Off) option, which is available for Nova’s Galaxy Series UPS systems.


The EPO option is intended to allow the user to have a method of immediately turning off all output power from the UPS. The normal method of power off is for the user to “hit’ his EPO for the room or facility. This would remove all power from the room and the equipment would normally stop operating. Due to the presence of the UPS battery, the UPS will see the removal of input power as a power failure and it would continue full, uninterrupted operation of the battery.

In order to allow the UPS to differentiate between a power failure and an EPO event, the UPS is outfitted with a special circuit breaker in the battery circuit. When the customer’s EPO circuit is activated, the EPO signal is used to also trip the battery circuit breaker associated with the UPS.

There are several ways in which the battery circuit breaker may be tripped. Some applications work by the momentary or temporary application of voltage to the trip coil of the battery circuit breaker. This voltage may be low or high, and may be AC or DC. It is important to specify these details when working with a Nova applications engineer as the UPS specifications are being determined. The most popular choice of circuit breaker trip coil is customer-supplied 24 VDC.

Alternative choices of circuit breaker trip voltages include the actual battery voltage. In that case, we momentarily pass the battery voltage through the trip coil of the circuit breaker. The circuit is completed through the customer’s EPO button. The circuit is not isolated and must not be grounded. Additional choices of circuit breaker trip are available upon request.

Some applications require the EPO function to also trip the AC input to the UPS. While this is not normally the case, Nova can accommodate these special applications.

Please consult with an applications engineer at Nova for assistance with the EPO option by inquiring via our contact page.