A road tanker is often the largest potentially isolated conductor which is brought on site and if incorrectly grounded, may pose a significant ignition risk.

When filling and emptying road tankers, both CLC/TR 50404 and NFPA77 recommend that fully interlocked static earthing systems are used (see CA09 - Earthing of a road tanker). However, in cases where an interlock is not possible, a self-testing clamp unit provides operator feedback via the LED indicator, ensuring that a low resistance ground connection has been made through paint or rust etc. to the metalwork of the tanker chassis. For remote working areas or infrequent operations, battery powered versions are preferred, while if frequent earthing operations are involved, a mains “line voltage” powered unit (fed via a certified Power Supply/Intrinsically Safe Interface Unit) is recommended, and several Monitoring Units may be fed from a common PSU.

BS5958 states that: During loading the vehicle should be earthed .... so that the resistance to earth is at all points less than 10 Ohms (7.2.1)

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