Our technical engineers answer your questions on a variety of topics, from circuit-breakers and work certification to cable supports and RCDs.
We have been asked to install some additional lighting on existing circuits within a school. All of the additional lighting will be installed using surface-mounted conduit. However, the existing circuits that wear extending are wired using thermoplastic insulated and sheathed cables buried in the walls. Do we need to upgrade the circuits to include additional protection?
The alterations/additions that you are undertaking on the existing circuit(s) would need to meet the requirements of BS '7671 (641.5). However, this would not necessarily require the existing circuit to be upgraded, provided that there were no defects or omissions that would affect the safety of your alterations or additions.
Any defects identified on the existing circuits that would not affect the safety of your planned works should be recorded on the certification produced, in accordance with the requirements of regulation 644.1.2.
Can switching off a BS 3871circuit breaker be used to provide isolation?
BEAMA, formerly the British Electrotechnical and Allied Manufacturers' Association, states insection 3.2.2 of its publication Guide to Low Voltage Circuit Breakers Standards that while "circuit breakers conforming to BS EN 60898 are suitable for isolation ... miniature circuit breakers (MCBs) manufactured to earlier standards (such as BS 38'71) are unlikely to be suitable for isolation".
As such, it would be necessary to seek advice from the particular manufacturer of a device to BS 38'71 to determine its suitability, or otherwise, for such use.
This BEAMA guide, and many others of interest to electrical contractors, are available as a free download from the BEAMA website:
beama.org.uk
We are working in a domestic apartment block and have been questioned over the types of cable supports that we have installed. Within the communal area where a suspended ceiling is to be installed, we have supported the cables using steel ties toa cable tray system. Within the individual apartments, where a solid plasterboard ceiling is to be installed, we have used cable anchors and plastic ties. Should these also be steel ties?
Regulation 521.10.202 requires that all wiring systems shall be supported in such a way that, in the event of a fire, they will not be liable to premature collapse and result in an entanglement risk.
Typically, for cables that are installed above a plasterboard ceiling, it is likely that the means of support will remain effective for long enough to allow persons to egress the building and for firefighters to enter the building and deal with the fire etc. All the time the cables are contained within the ceiling void, and the plasterboard is intact, they are protected from the effects of heat and fire. It should also be noted that even in the event of the plasterboards failing, the cables will pass through joists, where this is necessary for their routing, further limiting the likelihood of their causing an entanglement risk. For these reasons the use of plastic ties or clips in a floor void above a plasterboard ceiling is acceptable.
We have been asked to replace a number of fans within a domestic apartment block. The fans are to be replaced on a like-for-like basis, with no alteration being necessary to the fixing wiring. Do we need to certificate this work?
NICEIC would recommend that details of the work carried out are docunted using a Minor Electrical Installation Works Certificate (MEIWC), works order, job sheet or similar.
Is the provision of additional protection by a residual current device (RCD) required for the supply circuit to an electric shower installed in zone 1 of a location containing a bath or shower?
Yes. Additional protection provided by an RCD conforming to the characteristics specified in regulation 415.1.1 is required for all low-voltage circuits serving the location.
It should be further noted that any low-voltage circuits passing through zones 1 and/or 2, although not serving the location, must also be provided with additional protection by RCD (701.411.3.3).
