The ZERO-Hertz trip unit is a solid state overcurrent device for use on one and two pole DC circuit breakers in voltage classes up to 1,000 volts. The ZERO-Hertz® comes standard with long-time, short-time, instantaneous, ground fault, and reverse current. All of the protective features except long time can be turned off to allow for greater coordination and flexibility of use.


Programming the ZERO-Hertz

Done using the buttons and 16 character backlight LCD display on the front of the unit. An integrated security key prevents accidental modification of settings.

LCD Display

All settings are made in amps and seconds. The LCD displays the current during normal operation and shows the phase currents and type of trip after an event. 

Front Panel Data

The number, type of trip events and commissioning data are accessible from the front panel. This data can also be cleared or modified at anytime from the front panel. 

Testing for Perfection

The ZERO-Hertz also has a “SELF TEST OK” led that verifies the unit is functioning properly. There is also a “PICK-UP” LED that indicates when the current reaches or exceeds the long-time pick up value.

ZERO-Hertz® Features
  • True TRMS Sensing
  • DC and AC power input available
  • DC Shunt available
  • 50mV or 100mV DC metering shunts can be used
  • Hi-Range and Low-Range transducers available
ZERO-Hertz® Features
  • User configurable alarm relays available
  • Trip Unit with transducers can be calibrated
    using a high current AC test set
  • RS485 communications port with ModBus protocol
  • Secondary test set available
  • Retrofit Kits available for multiple breaker types

Phase, Split Core and Custom CTs


  • Primary ratings available range form 100A up to 6000A.
  • Each utility Relay CT is dual tapped for added versatility.
  • The standard secondary rating is 1.0A
  • Each CT is ratio and polarity tested several times during production

All CTs are specifically designed for use with the AC-PRO family of trip units.

Utility Relay Company manufacturers split core CTs for use as neutral CTs in 4 wire systems. The split cores make it very easy to install the CT on existing bus or cable. Each split core has phenolic plates with punch outs to match standard sizes/shapes of cable or bus-work.


  • URC split core CTs are designed for use as neutral CTs only
  • Each split core is dual tapped at full and half with a standard 1.0A secondary
  • The split core CTs are available from 225A to 4000A
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