Overwatch HEFPD Installation Schematics


Dairyland’s Overwatch HEFPD is a new class of device, designed using our decades of experience in high-energy applications. With a design featuring Dairyland’s proven solid-state technology, Overwatch can withstand the powerful, long-duration events caused by AC faults, keeping sensitive track-connected equipment protected. Overwatch is rated up to 4000 amps for a 12 cycle (0.2 second) duration AC fault event as defined in AREMA 11.3.7, while also meeting the applicable requirements of primary surge protection as defined in AREMA 11.3.1.

This article provides information on how an Overwatch High-Energy Fault Protection Device (HEFPD) can be shown in relation to the wiring schematics of the railroad line diagrams.  Overwatch has multiple options for the rail wire to terminate between the HEFPD terminals A, B, C or D with a fuse either in or out of circuit. Please refer to the Overwatch HEFPD Application Guide for more information on how these termination options can affect the fault ratings and overall protection of the bungalow equipment.

Please note, this article focuses on the rail-to-ground application only. For rail-to-rail equalizer or isolation joint wiring examples and ratings, please reference the Overwatch HEFPD Application Guide.

Rail-to-Ground Fault Protection Summary

When an Overwatch HEFPD is selected to protect signaling equipment in the bungalow, it is installed in the circuit between the rail and the bungalow using the track connected signaling wires. This application is known as rail-to-ground fault protection. Diagram 1 illustrates a track circuit one line diagram showing the track segments and train signals located at a road crossing, with a main track (T1) and a side track (T2).


Diagram 1: Road Crossing with a Side Track


Existing Wiring

The track connected wires are typically a twisted pair of #6 wires that connect to each rail and terminate inside the bungalow onto an entrance board with surge protector devices (aka lightning arrestors) prior to their connection to signaling equipment. Detail 1 shows these existing track connected wires going into the bungalow (B) in the area of X3 and X5 on tracks T1 and T2. The wires for the main track (T1) are labeled T1S1 and T1N1. The side track (T2) utilizes wires T2S1 and T2N1


Detail 1: Existing Track Connected Wires


Overwatch HEFPD Installation Details

In this scenario, two Overwatch dual-channel devices will be connected to the track signaling wires as shown in Detail 2. Note that each dual-channel enclosure will protect two rails. In this case, Overwatch-1 is protecting the main track (T1) through wires T1S1 and T1N1. Overwatch-2 is protecting the side track (T2) through wires T2S1 and T2N1. Note that a grounding wire is connected from Overwatch-2 to the existing bungalow grounding ring.

Overwatch can be mounted either outside the bungalow, or if room allows, inside the bungalow. Its enclosure is weather rated for outside exposure (NEMA-4X) and constructed of a powder coated stainless steel. Overwatch is designed for Wayside Class B outdoor installation per AREMA part 11.5.1.  The Overwatch HEFPD Installation Instructions have more information on mounting the enclosure.


Detail 2: Overwatch HEFPD shown between Track and Bungalow


Overwatch HEFPD Terminations

The track connected wires and the grounding wire will enter the Overwatch HEFPD enclosure through holes made by the installer at the bottom of the enclosure, utilizing rated conduit and conduit seals for the installed location. Detail 3 shows the wire connections made inside Overwatch-1 onto the provided terminals (or utilize a rated ring terminal on each wire end).

Note: this example uses the track wire connection option with the incoming rail wire terminated at A and the wire to the bungalow terminated at C, where the fuse is in the track circuit for a fault rating of 2000A. This is shown in Figure 1B of the  Overwatch HEFPD Installation Instructions. See this document for more details regarding mounting Overwatch and other wiring connection options.


Detail 3: Track Wire and Grounding Wire Terminations inside Overwatch for T1


Rail Schematics with Overwatch HEFPD

Overwatch HEFPD can be shown as a fused surge and fault module in the schematics of the track wiring diagrams. Overwatch is installed upstream of the bungalow terminal board that has the surge protection devices (or lightning arrestors). See Detail 4 for an example schematic for the referenced Terminal A to Terminal C connection of the rail-to-ground application shown in the details above.


Detail 4: Bungalow Termination Schematic


Dairyland Support: We’re Here to Help

Additional installation details may be found in the Overwatch HEFPD Technical Literature and Installation Instructions. If you have any questions on the application of an Overwatch HEFPD on your track segment, please contact Dairyland Technical Support for guidance.

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