I am looking at converting my garage into an office, will I need any additional electrical equipment as I hope to install extra plugs and light sockets?
If the garage is attached to the house, existing lighting and power point circuits could possibly be extended. The existing load would have to be calculated to ensure the circuits are not overloaded and comply with the current BS7671 Regulations.
We try to limit the amount of lighting points to a maximum of ten points per circuit, although with many modern lights and lamps the total current may not be very high. The limit is beneficial to the user as if a fault occurs it is easier to locate and causes minimal inconvenience.
Ring mains can often be extended and if this is done correctly (the ring is still complete) then many more sockets can usually be added. The extension is only limited by the total area that the ring circuit covers, as defined in the IEEE Wiring Regulations to 1002metres per ring main. Most domestic properties have two or three ring circuits, so this falls well within the limit. For maintenance purposes, limiting the amount of points can make life easier if there are faults at a later time.
When someone spurs off the ring with extra points, the additional points are limited to a maximum of one twin point. One problem we frequently encounter is several twin points have been added on to a spur from the ring. The 2.5mm twin and earth ring main cable is normally protected by a 32 amp breaker. In a ring main the load current is spread across the two cables forming the ring, whereas in a spur the load is all on one cable. Since the single cable is rated lower than the protecting 32 amp breaker, overloading can occur and will cause serious problems.
If the new garage/office is detached from the property, the situation is more complicated and you may need a separate feed to a new distribution board to supply the lighting and power circuits.
An earth stake may also be required to provide a sepearate earth system from the main house. This work would need notifying to building control.
Original questions from Simply Spalding and answers provided by Kelvin Goulden