How to carry out electrical second fix

Helpful video reference. We use Thomas Nagy's "SECOND fixing + my tips on LIVE installation" as the reference here. Thomas is a London-based electrician who runs the Electrical Highways Company. His video is filmed on a real UK domestic job and covers the sequencing and safety points that matter, including when to keep the board off during second fix.

1. Pull cables through and prepare ends

Start at the accessories. Pull each cable clear of the plaster by 150 mm or so, enough to dress neatly into the back box without strain. Use a sharp knife to remove the outer sheath, stopping well clear of the box edge so no bare sheath end sits inside the terminal. Strip each conductor to the terminal manufacturer's recommended strip length, usually 8--12 mm.

The circuit protective conductor (the bare copper) must be sleeved in green-and-yellow PVC sleeving before it goes into any terminal. Cut the sleeving to length, push it on, and make sure it covers the conductor right to the terminal entry. Bare CPC inside a metal back box is a common EICR finding.

2. Connect sockets

Standard 13 A socket outlets have three terminals: L (line, brown conductor), N (neutral, blue) and E (earth, green and yellow). Ring circuit sockets take two cables: both line conductors into L, both neutrals into N and both CPCs into E. Radial sockets take one cable each.

Tighten each terminal firmly. A conductor you can pull free with finger pressure is a fault waiting to happen. After tightening, give each conductor a gentle tug to confirm it is secure. On metal back boxes, fit an earth tail from the earth terminal on the socket to the earth terminal inside the back box itself.

3. Connect switches

Light switches work on the switched live, not the supply neutral. In modern brown-blue-green/yellow cable, the brown conductor at the switch is the permanent live and the grey or the second brown is the switched live returning to the fitting. Mark any repurposed conductor with brown sleeving or tape at both ends to show it is live when the switch is on.

For two-way switching, the switch cable has three-core and earth: brown to COM, grey to L1, black to L2 (or follow the specific colour code of the cable you ran at first fix). Confirm both positions switch the light correctly before fitting the faceplate.

4. Wire ceiling roses and light fittings

Loop-in ceiling roses have three sets of terminals: the supply loop-in terminals (both supply conductors go here), the switch terminals (switched live out to the switch and return), and the outgoing terminals to the lamp. Identify which cable is supply and which is the switch drop from your first-fix labelling, or by testing with a voltage tester if the circuit is being brought in live for testing.

If fitting a direct-wired pendant or semi-flush fitting instead of a rose, the connections are the same but made inside the fitting or with a Wago 224 pendant connector on flex.

5. Dress the consumer unit

At the board, each circuit tail needs to be stripped, sleeved on the CPC, and landed correctly. Line conductors go to the MCB or RCBO, neutrals to the neutral bar or the RCBO neutral terminal, and CPCs to the earth bar. Dress the tails neatly so the board can close, and label each way clearly before the board is energised. An unlabelled consumer unit is a problem for every electrician who works on the property after you.

6. Dead tests before energising

This is the step that cannot be skipped. Before the main switch goes on, run through the BS 7671 Chapter 61 dead tests on every circuit:

• CPC continuity: with the line disconnected at the board, link line and earth at the furthest point and measure R1+R2 at the board. Check it against the expected value for the conductor size and length.
• Ring final continuity: for any ring circuit, carry out the three-step ring test to confirm the ring is unbroken and correctly wired.
• Insulation resistance: at 500 V DC, measure between line and neutral (with them linked together) and earth. Minimum 1 MΩ per circuit; a healthy new circuit reads much higher.
• Polarity: confirm line is on line terminals throughout, not crossed to neutral at any point.

Record every reading. These become the Schedule of Test Results on the Electrical Installation Certificate.

7. Energise and live test

With dead tests passed, close the board and energise circuit by circuit. For each circuit carry out a live earth fault loop impedance test (Zs) and, where an RCBO or RCD protects the circuit, a timed RCD trip test at the rated current and at five times the rated current. Record these on the certificate.

Test every socket with a plug-in socket tester to confirm polarity and earth presence at the outlet. Test every switch. If an RCBO trips during live testing, isolate, investigate with the dead tests and fix before re-energising.

When to call us

Second fix on a rewire or new installation is Part P work. Richard carries out the full sequence from pulling cables through to the Electrical Installation Certificate. If you have done the first fix yourself and need an electrician for second fix and testing in Sandwich, get in touch.