8.6.3 Current Measurement Systems
RF current measurements may address several distinct quantities. Induced limb current is a reference-level quantity over the frequency range specified by the applicable exposure standard. Contact current concerns current that flows when a person touches an energized conductive object. Current in a cable, grounding conductor, tower member, or other structure can help identify the source of a potential hazard, but it is not automatically equivalent to limb current or contact current.
A clamp-on RF current probe can measure conductor current without disconnecting the conductor, as shown in Figure 8.4. The probe senses the magnetic field produced by current through its aperture and converts that response to a current value. Its frequency range, transfer impedance, conductor position, external-field rejection, dynamic range, and calibration configuration affect the result.
Measurements intended to demonstrate compliance with a limb-current reference level must use the quantity, instrumentation, body model, and averaging method specified by the applicable assessment standard. Contact-current measurements may support risk assessment, but RPS S-1 does not define a contact-current exposure limit. Procedures in AS/NZS 2772.2 that were developed for the superseded RPS3 contact-current limits may inform an investigation, but those former limits must not be treated as current RPS S-1 compliance criteria. A current measured on a nearby conductor may support hazard identification and control design, but does not by itself demonstrate the current that would flow through a person.
Conductor-current measurements are also useful for diagnosing common-mode currents, ineffective bonding or grounding, unintended coupling, and current paths on transmission lines, cable shields, towers, guy wires, vehicles, or other large structures. They supplement rather than replace electric-field, magnetic-field, and dosimetric assessments.