Wiring Regulations - Metal Consumer Units & TT Supply

Problems in using a metal consumner unit on a supply with TT earthing.

The Video

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A TT supply typically has an earth impedance which is too high to cause fuses or other protective devices to operate in the even of a line-earth fault.

Traditionally either an insulated consumer unit was used, or a separate RCD in an insulated enclosure was installed before the consumer unit.

BS7671 17th edition Amendment 3 requires that consumer units and similar enclosures are 'non-combustible' i.e. steel, creating a problem of how to ensure adequate prtection when a TT supply is used.