Guidelines on Earth Grounding for Irrigation Systems

Installers are obligated to establish a connection to earth ground for all electronic irrigation equipment in compliance with Article 250 of the National Electrical Code (NEC). The grounding configuration should include, at minimum, the components described in the following guidelines.

Selection of Grounding Electrodes #

Installers must use grounding electrodes that are either UL-listed or meet the specifications of Article 250-52 of the 1999 NEC. The grounding circuit setup will require the inclusion of a copper-clad steel ground rod, a solid copper grounding plate, and about 100 pounds of PowerSet® or equivalent earth contact material.

Installation of Ground Rods #

The ground rods should be a minimum diameter of 5/8 inch and a minimum length of 10 feet. These rods should be driven into the soil either vertically or at an oblique angle not exceeding 45 degrees. The chosen location for the rod must be at least 10 feet away from electronic equipment, as detailed in accompanying diagrams. Each rod should bear the UL logo for verification purposes. A connection is to be made with a 6 AWG solid bare copper wire of approximately 12 feet, utilizing a Cadweld GR1161G “One-Shot” welding kit or equivalent. This wire is then attached to the ground lug of the electronic equipment.

Grounding Plate Assemblies #

In accordance with Article 250-52(d) of the 1999 NEC, copper grounding plate assemblies should conform to specified dimensions and be composed of a copper alloy suitable for grounding purposes. A 6 AWG solid bare copper wire of 25 feet in length should be weld-attached to the plate by the manufacturer and connected to the equipment ground lug. The grounding plate must be buried at least 30 inches deep, or below the frost line if it extends deeper than 30 inches, and located 8 feet from the electronic equipment. PowerSet® material or equivalent should be distributed evenly around the copper plate within a 6-inch-wide trench. It is imperative to avoid using salts, chemicals, and other potentially corrosive materials as they deteriorate the copper over time.

Circuit Installation Techniques #

All components within the grounding circuit are to be installed linearly, avoiding sharp bends to minimize the risk of redirected energy into underground cables and wires. The proper spacing between electrodes must adhere to previously provided layout diagrams.

Resistance Measurement and Maintenance #

The resistance of the earth-to-ground circuit is to be measured with a device like a Megger®, ensuring it does not exceed 10 ohms. If the resistance is above the acceptable threshold, the installation of additional ground plates and PowerSet® is required. To maintain the efficacy of the copper electrodes, the surrounding soil should be consistently moist with a minimum moisture content of 15%, achieved by dedicating an irrigation station at each controller location to cover specified areas around the grounding components.

Connection Procedures #

All underground circuit connections need to be crafted utilizing an exothermic welding process, such as with Cadweld “One-Shot” kits or equivalent. Solder connections are prohibited. For successful ignition of the “One-Shot”, the recommended igniter to use is the Cadweld T-320 or equivalent. The 6 AWG bare copper wires installations must be straight, with any necessary bends forming sweeping curves with a minimum radius of 8 inches. While mechanical clamps may be employed temporarily during the resistance assessment, they must be replaced with permanent Cadweld “One-Shot” or equivalent connections immediately after testing.

Bonding #

It is important to recognize that this supplementary grounding is an additional measure beyond the equipment grounding conductor, often identified as “the green wire.” The conductive paths consisting of Black, White, and Green wires are required to be routed together, whether in a trench, conduit, or cable tray.

The grounding approach detailed earlier qualifies as “supplementary grounding” as defined by the National Electrical Code (NEC). For critical safety measures, the NEC mandates that all supplementary grounding systems be interconnected (“bonded”) with each other and with the primary grounding system at the service entrance (the point where the power source enters the building). This practice is also endorsed as the recommended protocol by IEEE Standard 1100-1999.

For the purposes of bonding, 6 AWG solid bare copper conductors should be used. However, if the system’s power conductors are larger than 1/0 AWG, the bonding conductors must be upgraded from 6 AWG to 4 AWG solid bare copper. Any connections involving these bonding conductors must be executed using a Cadweld “One-Shot” kit or equivalent to ensure a secure and permanent bond.

Shielding #

Bonding conductors should be positioned in a manner that enables them to serve as protective shielding conductors, forming a comprehensive coverage of solid bare copper wire across all primary groups of wires and cables.

This bare copper wire must be laid as close to the surface as feasible to avoid damage from ground maintenance equipment like aerators, yet deep enough to be protected from such interference. It should always be positioned above all other types of wires and cables, such as those for valves, power, and communication, in accordance with the specified detail, and deployed throughout all trenches as outlined in the electrical plan drawings. It is unnecessary to extend this conductor over minor wire runs (less than 150 feet) that deviate from the principal wire clusters. The conductor should be installed in as linear a fashion as possible, with any necessary turns made gently, adhering to the provided guideline for sweeping bends.

Important: To ensure the required sweeping bend when connecting bare copper wires to an electronic device’s ground lug, route it through a 1 ½” plastic sweep ell.

This shielding network must be connected to the service entrance’s earth ground, to the ground lugs of all electronic equipment, and to all supplementary grounding electrodes associated with the equipment. Each power source must have its own such network without interconnections between the equipment ground wires from various power sources.

For splicing bare copper wires, utilize an ERICO PG11L “One-Shot” kit or equivalent to ensure reliable and effective connections.

Wires and cables #

Power Wiring (120 VAC or 220 VAC): #

All electrical power cables are specified as Tray Cable, designed to meet UL standards for direct burial and have a voltage rating of 600 volts. Each cable will include three conductors, identified either by coloring or numbering as 1, 2, and 3, and will adhere to coding conventions using 3M #35 Vinyl Electrical Color-Coding Tape, consistent with code and industry norms. The dimensions of the “hot” and “neutral” conductors will be determined as per the irrigation design documents, while the “ground” conductor size will comply with or exceed the requirements set by the National Electrical Code (NEC). These cables feature copper conductors insulated with a high dielectric strengthen material made of PVC and Nylon. Additionally, the external jacket, made of black PVC, is engineered to resist degradation from sunlight exposure.

Control Valve Wiring (24-volt AC, nominal): #

The wiring utilized to establish connections between remote-control valves and the irrigation controller consists of single-conductor, PE-type wires. These contain a solid copper core and are enveloped in polyethylene (PE) insulation with a minimum thickness of 0.045 inches. Designed to be fit for direct burial specifically within irrigation setups, these wires are UL certified and guaranteed to function at a baseline of 30 VAC. The selection of wire sizes and colors will be guided by the details laid out in the irrigation plans and accompanying documents.

Disclaimer: Hydro-Rain has made every effort to ensure that the information and recommendations contained within are correct. However, neither Hydro-Rain nor any of its employees warrants nor accepts any liability for the use of this information. National and local electrical codes should always be followed. Wiring, grounding, shielding, and bonding irrigation system components often require competent engineering judgment on a case-by-case basis. Competent engineering assistance should be sought from firms specializing in this field.

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