When railroad systems share common corridors with overhead power transmission or distribution systems, they are susceptible to damaging power line fault and lightning surge events. Dairyland’s Overwatch HEFPD was designed using our decades of experience in high-energy applications to withstand the powerful, long-duration events caused by AC faults. Developed in response to the new AREMA C&S Manual Part 11.3.7 for High-Energy Fault Protective Devices, Overwatch will protect your track-connected signal and crossing warning systems and prevent costly interruptions.

Railroad systems are increasingly required to operate in a common corridor with power transmission and distribution lines presenting new equipment protection challenges. Damaging AC faults caused by failure of power utility equipment on overhead power lines present high energy, long duration events that typical lighting surge protective devices are not capable of withstanding. Unlike lightning surge events which have an extremely short duration measured in microseconds, high-energy AC faults can last for up to two seconds creating significantly higher total energy than traditional lightning surge arrestors are designed for. These events pose a risk to trackconnected signaling and crossing warning systems as well as other protective equipment. These damaging occurances were recognized by the railroad industry and became the basis for an entirely new class of device. AREMA Manual part 11.3.7 provides detailed guidance regarding the performance of highenergy fault protective devices (HEFPD).

Dairyland’s Overwatch HEFPD is suited for protecting sensitive track-connected equipment such as signaling circuits. The Overwatch has been extensively tested for its capability to withstand repeated high-energy AC faults. In addition, the Overwatch may serve as a primary lightning surge arrestor, meeting the applicable requirements of AREMA Manual part 11.3.1. Key characteristics of the Overwatch allow it to be track connected while minimizing the probability of a low impedance rail-to-ground or rail-to-rail failure.

AREMA CLASS 2000: AC FAULT CURRENT

• 2000A at 6 cycles
• 2000A at 12 cycles
• 1265A at 30 cycles
• 894A at 60 cycles
• 632A at 120 cycles

AREMA CLASS 4000: AC FAULT CURRENT

• 4000A at 6 cycles
• 4000A at 12 cycles
• 2530A at 30 cycles
• 1789A at 60 cycles
• 1265 at 120 cycles

UNTRIGGERED ELECTRICAL CHARACTERISTICS

• MCOV Rating: 50V-AC +/- 3V-DC
• 100 Ohm min. DC to 1kHz
• 3mA max, 3rd & 5th Harmonic, 20Hz to 500Hz

TRIGGER VOLTAGE

• 100V rms +/- 10% (142V peak)

LIGHTNING SURGE PROTECTION 

• 20kA, 8x20 microsecond waveform
• Peak let-through: <1,000V
  40kA, 8x20 microsecond waveform
• Peak let-through: <1,500V
  Fully functional after 15 repetitive tests at 40kA, 8x20

ENCLOSURE

• NEMA 4X 
• Powder Coated, Stainless Steel
• Lockable

Model Number Description Chart

There is an accessory available for the Overwatch HEFPD.