Electricity + Control April 2016

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John Wilson specialises in Metrology and Accreditation
consultation and training. He is a Senior member of the SA
Institute of Electrical Engineers, a Fellow of the Society for
Automation, Instrumentation, Measurement and Control.
John has over thirty years’ experience with Fluke products
(including having worked directly for Fluke) and has practical
experience in different fields of metrology and electronic
design. John has recently presented ECSA CPD Point Approved Seminars on
this subject at Comtest’s Linbro Park Offices.
Enquiries: John Wilson. Email
TRANSFORMERS + SUBSTATIONS
Figure 5: Stake positions for the 62 % rule.
take note
• Most facilities have grounded electrical systems – in the
event of a lightning strike, current will find a safe path
to earth.
• A ground electrode provides the contact between the
electrical system and the earth.
• Electrical codes and standards specify a minimum
impedance for the ground electrode.
References
[1] IEEE 142. 2007. Recommended practice for grounding of industrial
and commercial power systems (‘Green Book’).
[2] IEEE-81. IEEE 81. 2012. Guide formeasuring earth resistivity, ground
Impedance, and earth surface potentials of a ground system.
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