Q & A of the Day - Should I install a one- or two-way 100mA trip?

This Q & A of the Day is one of thousands answered by our Voltimum Experts on a daily basis in our Technical Expertise area.

Question: I've been asked to install a new circuit to a TT system that is protected by a voltage-operated trip. There is no spare way on the very old fuse board, and the customer does not want to pay for the trip to be changed.

Note that the circuit is totally surface-installed load side of this device using a suitable double-pole connection block. It is recommend that the existing installation be upgraded.

As I am only responsible for the new circuit feeds fixed equipment (solar PV), can I install a one- or two-way 100mA unit?

Answer: Regulation 131.8 of BS 7671:2008 requires that before any addition or alteration is made to an existing installation, the installer must establish that the condition of existing equipment will be adequate for the altered circumstances.

As this device has been used to achieve fault protection in this installation, any alteration or modification would necessarily depend on its reliable operation.

Voltage operated earth leakage circuit breakers (VOELCBs) have never been recognised by BS 7671 as devices suitable to provide fault protection. Therefore the continued use of this device would indicate a departure from BS 7671:2008.

Where encountered in service in older installations, the installer would be required to establish the functionality of the device under simulated fault conditions using appropriate test instruments or by operating the integral test button before accepting it as satisfactory for continued use. For further guidance please refer to the NICEIC publication 'Snags and Solutions, Part 3 Inspection and Testing, snag 25'.

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