Upgrading a consumer unit is not simply a matter of removing the old unit, mounting the new and reconnecting all the wires.
Below we will follow the upgrade of a very old consumer unit consisiting of of four rewirable BS3036 fuses and a main switch housed in an old wylex bakelite fuse box.
An extra lighting circuit and cooker circuit were to be added to the dwelling and there was no longer any space in the fusebox. With no RCD protection on any of the circuits and no space in the fuse box to add more circuits, adding RCD protection external to the fusebox to bring adequate protection to the new circuits was a non starter. An upgrade from a simple BS3036 fuse box to an 18th edition consumer unit popoulated with RCBO’s (circuit breaker and RCD in one) was the plan.
The original installation seemed to have been carried out to some sort of a decent standard. Though over its 30 year or so history various spurs, boilers, electric showers etc had been added to the final ring main. The original lighting circuit was to be replaced and another added. The old emersion heater circuit was to be converted into a Radial and finally a new cooker circuit added.
Due to the History of the ring main circuit and the conversion of the emersion heater circuit. Full testing of these circuits (continuity and insualtion resistance at this stage) had to be carried out and then remedial work undertaken to improve them (removal of unneccessary spurs, wiring outside of zones, and an old shower fused connection unit etc).
The new circuits to be laid were also tested as a matter of course being a new installation.
With satisfactory test results the new consumer unit install can take place and there can be confidence that there are no underlying faults that would cause the RCBO’s to trip once the system is energised.
The new consumer unit was mounted firmly to a solid stone wall so as not to be mounted to anything flammable. There are two entries into the Consumer unit one in the side and one on the top left. Both sealed with entry glands to prevent entry of fingers or other small bodies/water.
All the circuits have their own type A RCBO (this protects both AC and DC faults) and all the circuits are covered by a Surge Protection device (SPD) which is protected by its own circuit breaker.
A key advantage of RCBO’s is each circuit is independant of the other in the event of a fault. Many systems today group circuits under one RCD meaning if there is a fault on any one of the circuits in that group the RCD will shut them all down until the fault is rectified.
My final word is to be wary of anyone offering a quick or cheap consumer unit upgrade. Your installer should conduct as much testing as possible before removing your old system and an intallation certificate including all the test results should be issued shortly after completetion.
Actually one more word, your consumer unit only has to comply to the regulations of the time it was installed. If it is still functioning as intended there is no nead to upgrade to the 18th edition regulations and install a metal consumer unit with modern protection. Do not let anyone sell you a service based on this premise. In the study above new circuits were to be laid which do need to comply with the currrent regulations. And so RCD’s now needed to feature in the system.