QuestionTime


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A Q


What is the difference between Earthing and Bonding?


Both Earthing and Bonding are associated with fault protection – but they are distinct fromeach


other in their purposes and general arrangements. Earthing is the name given to the


connection of the exposed conductive parts of an installation (such asmetallic enclosures of Class 1 electrical equipment) to themain earthing terminal of the installation. Bonding (or, to give it its full name,


equipotential bonding) is the electrical connection of the extraneous conductive parts (such asmetallic service pipes and exposed structuralmetalwork that are liable to introduce Earth potential) and exposed conductive parts within the installation to maintain themat substantially the same potential.Main binding connects extraneous conductive parts to themain earthing terminal of the installation. The purpose of earthing is to limit the


duration of touch voltages. The purpose of bonding is to limit themagnitude of such voltages. Formore details see the Autumn issue of


Switched on fromthe Electrical Safety Council (www.esc.org.uk).


Q


I amhaving a problemwith carrying out an earth bond test on an office desk fanwhich is a


Class I piece of electrical equipment. The trouble is I cannot get a good earth on the appliance and themetalwork screws etc are not sufficient.


A


The guidance in the IEE Code of Practice is that "The continuity test should bemade between


accessible earthedmetal parts and the earth pin of the plug." If earthedmetal parts are not accessible


they cannot be continuity tested.Make a note on the test record that the appliance is Class I but has no accessible earthedmetal parts and as such an earth continuity test cannot be performed. Another way to view this is that the reason


accessiblemetal parts are earthed is to provide protection against electric shock in the event of a failure in the basic insulation. If the part in question is not accessible there is no risk of electric shock.


A Q


Should I record the actual test results or is it ok to simply label the appliance after testing?


Labelling an appliance after PAT testing is good practice as it provides a clear indication to the


user that is has been safety tested and when the re-test is due. The label alone however does not provide


details of what tests were performed or the safetymargin betweenmeasured results and the allowable limits. Maintaining a record systemof dates, tests


carried out and other appropriate detailsmakes itmuch easier to demonstrate compliance with the EAWR 1989 regulations if the electrical safety of an appliance is ever brought into question. be tested.


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