How to use a torque screwdriver on electrical connections

Helpful video reference. We use a UK consumer unit wiring tutorial by andysims on YouTube, "Connecting up a Consumer Unit Wired in PVC Singles - Fitting MCBs and Using a Torque Screwdriver", as the video reference here. It demonstrates dressing and connecting PVC single-core cables into a consumer unit and shows the correct torque tightening technique for neutral bar connections, MCB terminals and the main incomer. The UK-specific practice of recording torque confirmation on the certificate is covered.

1. Why torque matters

An under-tightened connection has a small air gap between the conductor and the terminal. That gap adds resistance, which generates heat. Over years, the heat causes the insulation to degrade and the terminal to corrode further, raising resistance further still. It is a cycle that ends in a fire or a fault. BEAMA and Electrical Safety First guidance says all terminations should be checked at original installation and at every periodic inspection, using the manufacturer's torque setting.

Over-tightening is the other failure. Crush a 1 mm² stranded conductor in a neutral bar terminal and you can shear through some of the strands, reducing the cross-section and increasing resistance in exactly the same way as under-tightening.

2. Find the torque specifications

The settings you need are always on the consumer unit itself, printed on a label inside the enclosure, or in the installation instructions that come with the board. Do not guess. A typical domestic consumer unit might have:

• Neutral bar conductor terminals: 1.0–2.5 Nm (varies by manufacturer and conductor size)
• MCB or RCBO terminal screws: 1.0–2.0 Nm for the conductor terminal, often different for the busbar clip
• Main switch incomer terminals: 6–10 Nm (sometimes higher for larger incoming cables)
• Main earth bar: as specified, often 2.0–3.5 Nm for domestic

The same board can have five or six different settings. That is why a fixed-torque screwdriver (which can only be set to one value) is of limited use for consumer unit work. Buy or borrow an adjustable model.

3. Set the torque screwdriver

Adjustable torque screwdrivers have a collar you twist to set the target Nm. The scale runs round the handle. Set it to the value for the first batch of connections you are going to tighten, then work through all the terminals at that setting before changing to the next. This is faster than changing the setting after every screw.

Use the correct blade size. Too small a blade tip rattles in the slot and transmits inaccurate torque. Too large and you cannot reach recessed terminal screws. Most consumer unit neutral bar screws take a #2 Pozidrive or a medium flat blade; MCB terminal screws vary. Check before you start.

4. Tighten the neutral bar

Start with the neutral bar. Work from one end to the other so you do not miss any. Apply the blade to the terminal screw, press down firmly so the blade does not slip, and turn until you feel and hear the torque screwdriver click (clutch-type models) or the handle flex at the preset point (beam type). Stop at the click. Do not give it one more quarter turn to be sure: that extra turn is exactly what exceeds the limit and crushes the conductor.

5. Tighten the MCB and RCBO terminals

Change the torque setting to the value for the MCB terminal screws. For each protective device, there are usually two conductor terminals: the line conductor going out to the circuit, and in some cases the incoming feed from the busbar system. Some boards use a snap-on busbar where there is no terminal screw, so you just press the MCB onto the busbar and tighten the outgoing conductor only.

PVC single-core cables (singles) need the same care as twin-and-earth. The larger cross-section cores (10 mm², 16 mm² for shower or cooker circuits) often go into the main switch rather than into an MCB, and those terminals have their own higher torque setting.

6. Tighten the main incomer and earth bar

The main switch terminals carry the full installation load. They are the most critical connections in the board. Change the torque setting to match the main switch specification - usually considerably higher than the circuit terminals. Use a large flat blade or the correct Pozidrive. Apply a firm, controlled turn. The click on a good adjustable screwdriver is very distinct at higher settings.

The main protective bonding conductors at the earth bar also need torque tightening. The earth bar may have a different setting from the circuit earths in the neutral bar area, so check the board label again.

7. Second pass and recording

Vibration from drilling or general installation work can slightly disturb connections made earlier in the job. Once everything is tightened, do a second pass with the screwdriver on the same settings. Any that give a small extra turn before the clutch releases needed it. Record on the electrical installation certificate that all connections have been torque tightened per the manufacturer's specifications and the date it was done.

When to call us

Consumer unit work is notifiable Part P work. If you need a consumer unit replaced or upgraded in east Kent, Richard carries out the full installation including correct torque tightening and certification.