Helpful video reference. We use eFIXX's video "CONSUMER UNIT WIRING - Do you need to use a meter tail clamp?" as the reference here. eFIXX - The Electricians' Channel - produced this video in partnership with Lewden, which makes a purpose-designed meter tail clamp for its consumer unit range. The video shows what the clamp does, how it fits and why it matters for a properly finished consumer unit installation.
1. What a meter tail clamp does
Meter tails are the cables that run from the electricity company's cut-out fuse (the sealed unit in the meter cupboard) to the main switch inside your consumer unit. They typically use 25mm2 conductors and carry the full incoming current for your property.
At the main switch, each tail terminates in a large screw terminal. If the cable can move freely, any mechanical force on it - vibration, the cable's own weight if it loops before entering the board, or someone accidentally pulling it - is transferred directly to that screw terminal. Over time this can loosen the connection. A loose high-current terminal generates resistance, resistance generates heat, and heat at that point is a serious concern.
A meter tail clamp grips the cable sheath and anchors it to the consumer unit enclosure, so any strain is taken by the clamp rather than the terminal.
2. When a clamp is required
BS 7671 Regulation 522.8.5 states that conductors and cables must be supported and protected from mechanical damage and from undue mechanical stress at the point where they enter an enclosure. Whether a dedicated clamp accessory is needed depends on the installation:
- Tails entering from below and running straight up to the main switch. The cable weight is relatively well supported by the route itself. A clamp is still good practice but the installation may be compliant without one if the cable is well supported before it enters the board.
- Tails that make a bend before the main switch. Any bend in a 25mm2 cable creates a spring force that bears on the terminal. Strain relief here is much more important.
- Tails entering from the side or top. The cable weight acts sideways or downward at the terminal, creating a levering action. A clamp is important in these arrangements.
- Consumer units fitted on vibrating surfaces. In a garage or utility room where machinery runs nearby, vibration needs to be isolated from the terminations.
3. The Lewden MTC in detail
Lewden produces the MTC (Meter Tail Clamp) as an accessory for its consumer unit range. It is a plastic bracket that bolts to the internal frame of the Lewden enclosure and grips both the live and neutral tails together at a fixed point close to the main switch terminals.
The MTC comes with fixing screws and is designed to take 25mm2 tails. Fitting it requires no cutting or modification to the consumer unit: the bracket locates on existing fixing points inside the enclosure. The eFIXX video shows the specific bracket positions and demonstrates how the cables seat in the clamp before the main switch terminals are tightened.
One additional benefit of the Lewden MTC: it positions the tails correctly so that the first RCBO can sit immediately adjacent to the main switch, using the full width of the consumer unit rather than having the tails block a circuit position.
4. Options for other makes of consumer unit
Not all consumer unit manufacturers provide a purpose-made tail clamp. For boards without one, common alternatives include:
- Cable glands in the enclosure knock-outs. A correctly sized cable gland on the entry point grips the cable sheath and provides strain relief at the board wall. This is the standard approach for armoured cable entries and works for meter tails too.
- Cable ties anchored to the chassis. In practice, many installers use heavy-duty cable ties to anchor the tails to a convenient point on the enclosure frame. This is acceptable if the tie is properly secured and the cable cannot work free.
- Third-party clamp accessories. Some accessory suppliers offer universal cable clamps that can be retrofitted to most enclosures.
5. Checking terminal torque
A meter tail clamp does not substitute for correct terminal tightening. The main switch in a consumer unit has a specified torque value for its terminals, usually in the range of 10 to 20 Nm for a 100A device, and this figure is printed on the device itself or in the installation instructions. Using a torque screwdriver to tighten to this value is the only reliable way to ensure correct terminal clamping force.
Under-tightening is the more common error - terminals feel tight by hand but the screw has not reached the correct torque. Over-tightening can strip the terminal or deform the conductor.
6. What to look for on an inspection
If you are having an EICR (Electrical Installation Condition Report) carried out, the inspector will check the meter tails for:
- Adequate strain relief at the consumer unit entry point.
- No signs of overheating at the main switch terminals (discolouration of the insulation or of the terminal itself).
- Correct cable sizing for the supply rating.
- Correct identification of live and neutral conductors.
A missing clamp where strain relief is clearly needed may appear as an observation on the report. It would not typically result in a C1 (danger present) code unless there was already evidence of overheating, but it could be recorded as C2 (potentially dangerous) or C3 (improvement recommended).
When to call us
If you have had a consumer unit replaced and are unsure whether the meter tails have been properly supported, Richard can inspect the installation and advise. If the tails need a clamp fitting, that is typically a short visit as part of a fuse board inspection.
Consumer unit inspection in Sandwich?
Richard carries out EICR inspections and consumer unit inspections across east Kent, covering Sandwich, Deal, Dover and Ramsgate.
Contact Richard