What you need to know

What's involved?

A visual inspection of all the accessories without removal. (Accessories mean sockets, switches, fused spurs, light fittings, etc). Accessories are checked for cracks and evidence of overheating

A sample of accessories is removed, typically 10% so around 2 or 3 sockets. The sample may be increased if issues are found with the wiring of the removed accessory, for example, no green & yellow earth sleeve on the CPC (earth conductor) or no rubber grommet where the cable enters the back of a metal box.

Earthing and Bonding. The electrical installation must be earthed, and incoming metallic mains service pipes, such as water and gas, must be bonded. Earthing is identified by a green & yellow conductor from the cut-out housing the main fuse if your DSO provides an earth, or it may be a green & yellow cable to an earth rod in the garden in many rural areas. Bonding is identified by a green & yellow cable from the DB (Distribution Board, consumer unit, fusebox etc) to where the pipe enters the property, for water, this is usually near the stop cock and for gas, near the meter.

The Tests

In no particular order, the following tests are carried out as a minimum

CPC Continuity at every point. Regulation 411.3.1.1 says "A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed-conductive-parts and suspended from such a point." A CPC continuity test confirms that the earthing conductor is continuous from the last point in a circuit all the way back to the origin of the earthing, which could be the local substation, pole transformer or earth rod.

IR (Insulation resistance). The basic insulation surrounding a conductor, which is brown and blue or red and black for cables prior to 2006, slowly degrades over time; the degradation process is sped up if the cables get hot, get crushed, are chewed by rodents or come into contact with UV light or some chemicals. An IR test checks for continuity between the Live conductors (Including neutral) and the CPC. There should be no continuity; a result under 1 million ohms fails the test and will need investigation to find out why. Most new installations have a measurement of 999,000,000 ohms

r1, rn & r2 Continuity. Ring circuits are unique to the UK and were adopted after WWII to save copper in electrical installations. This test confirms that the conductor is intact from where it leaves the DB around the property and returns to the DB.

RCD Test. If the installation is RCD protected that it has to be tested to ensure it trips in time; typically less than 0.3s. The RCD can also be ramp tested to ensure it's not too sensitive. A ramp test introduces a current from 0-33mA and records the value when the RCD trips

Functional checks Circuit breakers, RCDs and main switches are switched off to ensure they work.

The Paperwork & Coding

The report has nearly 150 items that require one of the following: ✔️,✖️, N/A, LIM, C1, C2, C3, FI.

A ✔️ indicates this item is satisfactory. A C1 indicates that an immediate danger is present. A C2 indicates an item is potentially dangerous, C3 indicates that improvement is recommended, and FI means further investigation is required. As long as there are no C1, C2 or FI codes then a satisfactory report can be issued