Supply equipment
The service head (cut-out) — and why electricians can't touch it
Every UK supply enters the property through a service head — usually called the cut-out — containing the network operator's service fuse. It looks like part of your electrical installation, but it isn't: it is sealed DNO equipment, and there is a hard, industry-agreed line that electricians must not cross.
Terminology
DNO, DSO, service head, cut-out — the correct words
Service head / cut-out
The box where the service cable terminates, containing the service fuse (commonly rated 60, 80 or 100 A). “Cut-out” is the formal industry term; “service head” and “fuse head” are the everyday ones. It is the boundary between the public network and your installation.
DNO vs DSO
DNO — Distribution Network Operator — is the licensed company that owns the local network (UK Power Networks in Brighton, Hove and the South East). DSO — Distribution System Operator — describes the wider system-operation role those same companies are taking on. Either way, the cut-out belongs to them.
MOCoP (formerly MOCOPA)
The Meter Operation Code of Practice — originally the Meter Operation Code of Practice Agreement (MOCOPA), now version 2.0 under the Retail Energy Code — sets the safety, technical and interface rules for who may install, operate and maintain metering equipment, and how meter operators and the DNO interact at the service position.
Meter tails
The conductors from the cut-out to the meter, and from the meter to your consumer unit. The electrician's world starts at the meter's output terminals — but the tails upstream of the main switch still cannot be isolated by the consumer, which is why work on them needs proper coordination.
Who owns what
The three-way split at your meter position
DNO / DSO — Distribution Network Operator
Service cable, service head (cut-out) and service fuse
Everything up to and including the cut-out is the network operator's sealed equipment. You will increasingly hear 'DSO' (Distribution System Operator) — the same organisations taking on wider system-operation duties. For Brighton & Hove the operator is UK Power Networks. Only their authorised staff may remove the cut-out fuse, break its seals or replace the head.
Meter Operator (MEM / MOP)
The electricity meter and its immediate connections
Metering Equipment Managers work under the Meter Operation Code of Practice (MOCoP — formerly the MOCOPA agreement, now governed under the Retail Energy Code). Their accreditation lets them install, exchange and remove meters and work on the meter terminals — not open or replace the DNO's cut-out. A newer Safe Isolation Provider (SIP) role lets specially accredited metering operatives de-energise and re-energise a meter point in defined circumstances.
Your electrician (e.g. All Cabling Limited)
Everything from the meter's output terminals onwards — consumer unit, circuits, earthing and bonding on the installation side
The installation begins at the meter tails leaving the meter. A registered electrician designs, installs, tests and certifies everything downstream, but the cut-out, its fuse and its seals are out of bounds — however experienced the electrician is.
The reasons
Why the cut-out is off limits — even to a qualified electrician
It is always live
There is no switch between the street network and the cut-out. The service fuse is the only protection, and the terminals above it are live 24/7 at the full prospective fault current of the network — often several kiloamperes. An error here is an arc-flash event, not a tripped breaker.
It is sealed, owned equipment
The cut-out carries the DNO's seals. Breaking them without authority is tampering with network equipment and can be treated as interference with the supply — the same legal territory as meter interference. Seals also tell the DNO whether anyone has been inside.
Authorisation is contractual, not just competence
MOCoP defines exactly which roles may do what at the service position: DNO staff on the cut-out, accredited metering operatives on the meter, and (since 2023) Safe Isolation Providers for defined de-energisation tasks. A qualified electrician who is not in one of those roles has no authority to open the head — it is an industry-agreement boundary, not a skills judgement.
Safe isolation stops at the main switch
BS 7671 (Chapter 53, isolation and switching) gives the installation its own means of isolation — the main switch in the consumer unit. That is where an electrician's safe-isolation procedure applies. If a job genuinely needs the supply dead at the cut-out (for example, replacing meter tails or a consumer unit where the tails cannot be made safe), the correct route is to arrange isolation through the supplier's meter operator or the DNO — never to pull the service fuse.
Older equipment
Black phenolic resin cut-outs — the ones to watch
Between the late 1960s and the early 1990s, millions of homes were fitted with cut-outs moulded from black phenolic resin — the same family of brittle, heat-set plastic as old Bakelite fittings. Modern replacements are usually grey glass-reinforced polyester (GRP). The phenolic design is now old enough that network operators and industry bodies have raised specific concerns about how it fails.
How to recognise one
A black, hard, glossy plastic head — often with the fuse carrier pulling out from the front — rather than the lighter grey moulded GRP of a modern unit. If the property dates from the 1970s or 1980s and the cut-out has never been changed, there is a fair chance it is phenolic.
Insulation breakdown and tracking
The reported failure mode is the phenolic insulating material breaking down with age and heat, allowing current to track between the live and neutral sections inside the head. Engineers who investigated these failures describe catastrophic failure of the unit — and fires have been attributed to them.
Brittle with age
Phenolic resin grows more brittle over decades. A knock during meter work — or even a firmly inserted fuse carrier — can crack the housing, exposing live parts that cannot be isolated from inside the property. This is one reason meter operators receive specific guidance on these units.
Overheating under modern loads
These heads were designed for the loads of their era. EV chargers, electric showers and heat pumps push them closer to their limits for longer, and an overheating phenolic head may show scorching, a hot-plastic smell or fresh bitumen leaking from the base — all reportable defects.
Testing a suspect surface for voltage
If a surface around the meter position — the cut-out housing, its base or the meter box lid — is suspected of carrying voltage, it must be checked with a voltage contact indicator: a tester that detects voltage by making physical contact with the surface. These are pen-shaped, often single-pole (for example the Martindale VT7, CAT III 600 V / CAT IV 300 V to BS EN 61010), and they look very similar to a non-contact "volt stick" pen — but the two are not interchangeable. A volt stick senses a field through the insulation and can give false readings on a tracked or leakage-energised surface; a contact indicator gives a reliable result. Prove the indicator on a known source before and after use, as GS38 requires. If you are not a competent person with a proven contact indicator, do not test at all: keep away and report it on 105.
If you have one
Do not touch it, do not let anyone other than the network operator work on it, and do not attempt to pull the fuse carrier yourself. The industry position is that correctly installed units do not inherently pose a fire risk — but age, damage or signs of overheating change that picture. If your cut-out is black phenolic and shows any of the defect signs below, report it on 105. Replacement of a defective cut-out is the DNO's job and is normally free — it is their equipment. Paul will always flag a phenolic head in poor condition when he surveys or tests your installation.
Danger levels
Cut-out defects — how serious, and what to do
This is Paul's practical risk guide for customers, not an official MOCoP classification. The rule underneath it is simple: defects on service termination equipment are always for the network operator to assess and repair — your job is to recognise them, keep away and report.
Immediate danger
Signs: Exposed live parts, a cracked or broken cut-out casing, arcing, buzzing or crackling from the head, smoke, or any sign of fire.
Action: Keep everyone away, do not touch anything in the meter position, and call the network operator now — 105 (free, 24 hours) or UK Power Networks on 0800 31 63 105. If there is a fire or a risk to the public, call 999 first.
Urgent — same day
Signs: Scorch marks or discolouration on or around the cut-out, a burning or hot-plastic smell, a head that feels hot, fresh bitumen/pitch leaking from the bottom of an older service head (a classic sign of overheating), or a service cable that has come loose.
Action: Do not use high-power appliances until it is checked, and report it to the DNO on 105 the same day. They will normally attend and make safe free of charge — it is their equipment.
Report soon — non-urgent
Signs: A damaged meter box door or surround, old dried bitumen drips with dust on them, water getting into the meter box, a broken seal with no other damage, or perished cabling shrouds.
Action: Report to the DNO's non-urgent line or via their website defect reporting. Still their job to fix — but not an emergency if there is no heat, damage to live parts or water contacting equipment.
Report it
The numbers to call
105
The free national number for power cuts and electricity network emergencies — connects you to your local network operator, 24 hours a day.
0800 31 63 105
UK Power Networks direct — the DNO for Brighton, Hove, Sussex, Kent, London and the South East. Free from landlines and mobiles, 24 hours.
999
Fire, or electricity lines down and putting the public at immediate risk — emergency services first, then the network operator.
Problems with the meter itself (display, readings, smart functions) go to your energy supplier, who appoints the meter operator. Problems with your consumer unit or circuits are for your electrician — call Paul on 07770 880255.
Energy theft is reported separately from network faults. If you suspect a meter has been tampered with or a supply bypassed — at your property or anyone else's — Stay Energy Safe, run by the charity Crimestoppers, takes reports 100% anonymously at stayenergysafe.co.uk ↗ or on 0800 023 2777. You never have to give your name — and tampering puts you, your neighbours and your whole community at risk of fire, electrocution and explosion, so it is always worth reporting.
The one-line rule
If it is upstream of the meter, it is not yours and not your electrician's — keep the seals intact, keep your hands out, and call 105. For everything downstream, see safe isolation and UK earthing systems.