Campbell Scientific CR6 CR6 Measurement and Control System - Page 111

Section 7. Installation In the field, at a minimum, a proper earth ground will consist of a 6 to 8 foot copper-sheathed grounding rod driven into the earth and connected to the large brass ground lug on the wiring panel with a 12 AWG wire. In low-conductive substrates, such as sand, very dry soil, ice, or rock, a single ground rod will probably not provide an adequate earth ground. For these situations, search for published literature on lightning protection or contact a qualified lightningprotection consultant. In vehicle applications, the earth ground lug should be firmly attached to the vehicle chassis with 12 AWG wire or larger. In laboratory applications, locating a stable earth ground is challenging, but still necessary. In older buildings, new Vac receptacles on older Vac wiring may indicate that a safety ground exists when, in fact, the socket is not grounded. If a safety ground does exist, good practice dictates the verification that it carries no current. If the integrity of the Vac power ground is in doubt, also ground the system through the building plumbing, or use another verified connection to earth ground. Figure 34. Schematic of Grounds 7.6.1.1 Lightning Protection The most common and destructive ESDs are primary and secondary lightning strikes. Primary lightning strikes hit instrumentation directly. Secondary strikes induce voltage in power lines or wires connected to instrumentation. While elaborate, expensive, and nearly infallible lightning protection systems are on the 111