Decoder System Design

Earth Grounding

Earth Grounding of decoder systems is another part of installation that requires planning and careful installation. Properly grounded decoder systems perform very well even in regions with frequent lightning storms. Poor grounding often results in unnecessary equipment losses and irrigation down time.

Earth grounding rules for the ACC99D family decoder controllers are the same as for other ACC controllers. A large ground lug, or clamp, is provided for connection of bare copper wire to earth grounding hardware.

  • Install the grounding wire and earth ground hardware at right angles from the two-wire paths, when possible

Decoder installations also require earth grounding in the two-wire path itself, to protect the decoder investment. The ICD family of decoders features integrated surge suppression and each decoder module is equipped with a bare copper wire for connection to earth ground hardware.

Earth ground should be connected at every 12th decoder, or 1,000 ft/330 m of wire run, whichever is shorter. The station size of the decoders is not taken into account for grounding purposes… every 12th decoder module is the rule.

The final decoder in any wire run should be grounded. This includes the final decoders in each of the different arms of a "T", if the arm is more than 500 ft/150 m.

The DUAL Difference

DUAL decoders do not include integrated surge suppression. Instead, install the DUAL-S surge arrestors after every 12th decoder, or 1,000 ft/300 m, at a minimum. In high lightning areas, install more frequently.

The ground wires on intervening ICD decoders are not used. It is not necessary to remove the unused ground wire or bury it. Simply fold them out of the way (this allows future additional grounding or use of the decoder in another location).

Decoder grounding hardware should always be connected and placed at right angles to the run of the two-wire path. 

The use of a separate bonding wire in the trench between all grounded decoder points is not required, but can dissipate surge energy and help prevent pipe damage in the event of a lightning strike.

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