Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, about extraneous conductive parts and damp floors, is answered by The IET:
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Question: BS 7671 defines an Extraneous Conductive Part as 'a conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation'. I have been reading an article relating to electrical installations in detached garages and sheds, and my question concerns the provision of a separate equipotential zone in this type of situation.
My question relates to the earthy situation presented by the concrete floor in a detached garage/shed or, in the case of some sheds, the wooden floor. In both situations, the floor can introduce a potential, generally earth potential and it does not form part of the electrical installation so I would naturally assume that it would be considered to be an Extraneous Conductive Part. Is that so?
If this is argument is valid, then what practical means should be employed to effectively bond these points to the MET in this type of hazardous environment?
Answer: Yes, you are quite right. A wet floor can introduce earth potential. The risk of electric shock is increased because of contact with earth potential. I am assuming the person has wet footwear.
Please see Regulation 400-02-01. Regulation 471-08-01 also gives requirements.
Turning to Part 6, relevant requirements to be considered by the installation designer to provide adequate protection against electric shock might include 30mA RCD protection, better IP ratings for equipment (because of the wet environment), an earthed metallic grid (mentioned in 601, 602 and 605) the requirements in 606, and the use of ADRLV.
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