Ground Electrode Correspondence - RME111 - RWS200 - AWS310-SITE - AWS430 - RWCC - AWS310 - FOC201

Grounding and Lightning Protection in Vaisala Outdoor Installations Technical Reference

Document code
M211786EN
Revision
B
Language
English (United States)
Product
RME111
RWS200
AWS310-SITE
AWS430
RWCC
AWS310
FOC201
Document type
User guide

In a homogenous soil, the grounding resistance of a single 3 m (10 ft) rod is roughly equivalent to 6 m (20 ft) of a horizontal ground electrode buried approximately 0.6 m (0.2 ft) underground.

A 6-m (20 ft) diameter loop and three 6-m (20-ft) electrodes in a horizontal star is equivalent to three 3 m (10 ft) rods driven in 7.5 m (25 ft) spacing. In practice, the connection wires of the rods are also buried forming a smaller star by themselves so that they lower the resistance and the impedance.

Buried wire lengths can be extended to several tens of meters (several dozens of feet) with almost linear relation to grounding resistance value. In a very poor soil, a maximum length of nearly 50 m (150 ft) per wire may be needed, but it is more cost-efficient to treat the soil chemically.

Table 1. Typical Ground Electrode Length and Spacing
Minimum values Ground rod Horizontal ground electrode
Length Typically 3 m (10 ft) 10 … 30 m (33 … 100 ft), soil type dependent
Loop diameter 5 … 6 m (16 … 20 ft)
Spacing Min. 2 × rod length