Grounding for 2-Wire Systems

Introduction

This document provides essential information on grounding 2-wire irrigation systems manufactured by Rain Bird. Proper grounding is crucial for protecting controllers and field devices from electrical surges, lightning strikes, and for ensuring the overall reliability and longevity of the irrigation system. It also details the importance of ground resistance, system design, and maintenance.

The Importance of Grounding

A grounding system safely discharges lightning-induced electrical current into the earth, preventing it from traveling through power or field wires to sensitive electronic components. Effective grounding and surge protection significantly reduce the risk of damage to controllers and irrigation systems, thereby minimizing troubleshooting time and repair expenses.

WARNING: Failure to properly ground a 2-wire system can lead to controller failure and void the warranty. Always ensure grounding devices comply with local electrical codes.

Ground Resistance: Understanding the Basics

Ground resistance is the opposition to the flow of electricity into the earth, caused by grounding system components and the soil itself. It is measured in ohms (Ω). Lower ground resistance means a higher likelihood that surges will be shunted to the ground, away from electronic components. A ground resistance tester, such as the Megger DET3TC, can be used for measurement. A properly installed grounding system should maintain a ground resistance of 10 ohms or less.

Grounding Overview

Rain Bird offers various components and methods for grounding 2-wire systems, including:

• LX-IVM Components: Controller ESP-LX-IVM, Field Devices (IVM-SOL, IVM-OUT, IVM-SEN), Interface Module, Surge Device (IVM-SD).
• ESP-LXD Components: Controller ESP-LXD, Decoders (SD-211, FD-101, FD-202, FD-102), Interface Module (ESP-LXD-M50), Decoders with integrated surge protection (FD-401, FD-601), Surge Device (LSP-1).
• Grounding Rods: Typically 5/8" x 8' copper clad with welded insulated conductor.
• Grounding Plates: Typically 96" x 4" copper clad with welded insulated conductor.
• Restricted Spaces: Methods for grounding in areas with limited space or obstacles.

Connecting to Ground: Step-by-Step Installation

The grounding process involves several key steps:

Step 1: Grounding the Controller

The ESP-LX-IVM or ESP-LXD Decoder Controllers are protected by the primary ground of the incoming power. If this primary ground does not provide 10 Ohms resistance or less to ground, the transformer ground wire should be connected to a local ground rod or clamp that meets this resistance requirement.

Step 2: Grounding the 2-Wire Module

1. Connect a #6AWG copper wire to the ground lug of the M50 (ESP-LXD) or IVM 2-Wire (LX-IVM) Interface Module.
2. Connect the other end of the ground wire to a grounding system with a resistance to ground of 10 ohms or less.

Step 3: Ground each Star Path

For 2-Wire paths in a "Star" configuration, each path must terminate with a surge device (LX-IVM: IVM-SD, ESP-LXD: LSP-1, FD-401 or FD601) connected to a grounding system.

Diagram showing multiple paths connecting to grounding points via surge devices.

Step 4: Ground the 2-Wire Path

The 2-Wire path must be surge protected with a surge device (LX-IVM: IVM-SD, ESP-LXD: LSP-1, FD-401 or FD601) and connected to a grounding system every 500 feet or every 15 field devices (LX-IVM) / 8 field devices (ESP-LXD), whichever comes first.

Diagrams illustrating grounding intervals for LX-IVM and ESP-LXD systems.

Grounding System Designs

Rain Bird offers several grounding system designs:

Design 1: Single Grounding Rod

Grounding rods should be at least 5/8" x 8' copper clad with welded insulated conductor. Rods should be installed at a distance equal to or greater than their length from the 2-wire path or any electrical equipment. For example, an 8ft rod must be installed at least 8ft from equipment. The connecting wire should be installed in a straight line, with turns made in sweeping curves (minimum 8-inch radius, 90° included angle). To minimize resistance, the copper wire must be pre-welded or welded using an exothermic process.

Diagram illustrating a single grounding rod installation with its sphere of influence.

IMPORTANT: If you need to reduce ground resistance further, consider Ground Rod Stacking, Ground Enhancement, or a "Y" Grid Design.

Design 2: Single Grounding Plate

If there is a risk of hitting underground pipes or wires when driving ground rods, a copper clad 8 foot x 5/8 inch grounding plate can be used, provided it maintains 10 ohms or less of resistance. Grounding plates should be installed 30" below grade.

Diagram illustrating a grounding plate installation with its sphere of influence.

IMPORTANT: If you need to reduce ground resistance further, consider Ground enhancement material or adding additional plates.

Design 3: "Y" Grid

This design uses three, 5/8"-diameter x 8-foot-long grounding rods installed in a radial 120° "Y-shaped" configuration. Each rod must be installed vertically, at a distance equal to or greater than its length from the 2-wire path or electrical equipment. Connections between rods should be made with 6AWG copper cable welded with an exothermic connector.

Diagram illustrating a "Y" grid grounding system.

IMPORTANT: If you need to reduce ground resistance further, consider Ground rod stacking or Ground enhancement material.

Additional Grounding Techniques

• Ground Enhancement Material for Rocky or Sandy Soil: If a resistance of 10 ohms or less cannot be achieved, decrease resistance by surrounding grounding rods or plates with ground enhancement material, such as POWER SET from Paige Electric Corporation or GEM from ERICO.
• Dry Soil: Moist soil offers lower resistance. Rain Bird recommends irrigating the soil around the grounding system using a dedicated irrigation zone with sprinkler heads and a specific watering program. Install grounding components in irrigated areas or use emitters/bubblers in non-irrigated areas to maintain soil moisture.
• Ground Rod Stacking: Threaded couplers can be used to "stack" grounding rods if a single rod fails to produce adequate resistance. This increases the effective rod length and decreases ground resistance. Couplers should be made of the same material as the rods for a secure connection.

Maintenance

Measure the ground resistance around the grounding system after installation and annually thereafter. Grounding connectors should be accessible via a valve box for yearly testing with a ground resistance tester. Inspect the grounding system's clamped connections to equipment (not welded connections) annually to ensure they are secure and free from corrosion.

Diagram showing a ground resistance tester measuring ohms.