Cat5e, Cat6 & Cat6a — certified.

Practical advice on Cat5e, Cat6 and Cat6a — plus professional certification testing so your network performs exactly as the spec sheet says, not just "the lights come on at both ends."

Wired ethernet is still the most reliable network connection you can have in a building, and it isn't close. WiFi has improved enormously in the last ten years, fibre is now in plenty of London streets, but a properly installed and certified Cat5e or Cat6 run from a wall plate back to a patch panel will outlast the building it's in. I've been installing structured data cabling across London since 2011, and the cabling I dropped into a Camden office in my first year is still humming along on the same gigabit it was certified at. That's what you're paying for.

The questions I get asked first when somebody rings about ethernet are almost always the same: which cable do I need, how much disruption is it going to cause, and how will I know it actually works at the speed it's supposed to. The short answers are: probably Cat6 these days unless there's a specific reason otherwise; a lot less than you think if you let a real engineer plan the routes; and you'll know because I'll hand you a printed Fluke certification report at the end. The long answers are below.

Which cable should you choose?

There are three categories I'll routinely install in a residential or small-commercial setting: Cat5e, Cat6 and Cat6a. They're all four-pair twisted-pair copper, terminated on RJ45 connectors at either end, and they all look broadly similar in the wall. What changes between them is the construction quality of the twists, the thickness of the conductors, the presence or absence of a central separator, and as a consequence the bandwidth headroom they can carry over a given length. The tiles below set out what each is good for.

How I decide which one to install

For most domestic installs in London — adding a wall plate in a home office, running a feed to a TV, dropping a couple of points into a kitchen-diner extension — Cat5e is more than adequate. It does a clean gigabit, the cable is flexible enough to bend nicely around joists and through tight ceiling voids, and it terminates faster which keeps the labour down. Anything you can stream to a modern TV or game on a console fits comfortably inside Cat5e's capability.

For new builds or major refurbishments where you're getting one shot at putting cable in walls that won't be opened again for twenty years, I'd default to Cat6. It costs slightly more per metre, it's slightly stiffer to work with, but the extra headroom means the install is futureproofed for the 2.5-gig and 10-gig home services that are starting to land on FTTP lines. Cat6 is the sensible "if in doubt, do this" choice for a new or extensively rewired property.

Cat6a is overkill in almost any domestic setting but absolutely the right answer for commercial installs, long runs over 50 metres, PoE-heavy environments where you're feeding access points and cameras down each cable, or any backbone link between cabinets where you genuinely want a stable 10-gig path. It's noticeably thicker, has tighter twist specs and tighter bend radius rules, and it costs more in both material and labour to install. I'd recommend it for a serious office fit-out but rarely for a house.

Cable testing & certification — the bit that separates a real install from a hopeful one

I use professional certification testers — Fluke DTX-1800 and the newer Fluke DSX series — to verify every cable I install against the relevant TIA and ISO/IEC category standard. A full test report comes printed on completion, one page per cable, with pass/fail for each parameter and the actual measured values alongside the spec limit. That report is yours; keep it with the house documentation or the lease, because it's also what the warranty hangs off.

• Confirms wiremap (correct pin-to-pin termination across all eight conductors).
• Measures physical length, propagation delay and delay skew.
• Reads insertion loss (attenuation) versus the category limit at each frequency band.
• Reads near-end crosstalk (NEXT), power-sum NEXT, ACR-F and ACR-N — the crosstalk margins that determine real-world speed.
• Reads return loss — the reflection of the signal back to source, a sign of bad connector terminations or kinks.
• Proves the install meets the category rating you've paid for, not just "the lights come on at both ends."
• Essential for any manufacturer's warranty and absolutely standard on business-grade installations.

Why cheap "beepers" aren't enough. The basic continuity testers builders and general electricians sometimes use only light an LED to confirm that pins connect to pins. They cannot assess high-frequency performance, crosstalk between pairs, return loss from impedance mismatch, or noise injection from neighbouring runs. They cannot certify your cabling. If you've paid for a category-rated install, insist on a category-rated certification report. Anyone reluctant to produce one is telling you something important.

Business data installs should always include a written warranty. With major manufacturer-trained installs (Excel, Connectix, Brand-Rex and similar) the warranty is typically fifteen or even twenty-five years when the cable, components and termination technique meet the manufacturer's spec and the certification report is filed with the warranty. That paperwork is part of the handover.

Network design — what good cabling looks like

• Star topology to a single cabinet. All new data runs from each room should terminate on a patch panel in a centrally located data cabinet, not spurred together in a daisy-chain. Each outlet gets its own dedicated cable home-run to the cabinet.
• Router and switch at the cabinet. The broadband router (or the ISP-supplied ONT and a dedicated firewall on a more serious install) lives in the cabinet. From there a gigabit or multi-gig switch fans out via the patch panel to each outlet around the building.
• Sensible cabinet location. Cool, dry, ventilated, accessible — ideally a service cupboard, the corner of a utility room or a dedicated cabinet on a landing. Not a stuffy under-stairs cupboard with central heating pipes running through it.
• Power and grounding. A small UPS in the cabinet keeps the network alive through brief outages. Earth bonding for shielded cable where applicable.
• Label and document. Every outlet, every patch lead, every patch-panel port labelled. A printed schedule and the certification reports go to the customer at handover.
• Future capacity. Always leave a couple of spare cables to commonly used rooms — pulling cable later is many times more expensive than running one extra on the same day.

I'm a qualified LAN design consultant and happy to produce credentials, design drawings and a structured-cabling specification on request. Larger commercial designs get a single-line diagram and bill of materials before any kit is ordered.

Real installs across London

An accountancy practice above a deli in Marylebone

An accountancy firm in W1 took on the floor above their existing office and asked for the new space wired up. The original building was a 1930s mansion block — lath-and-plaster ceilings, period mouldings, listed facade — so there was no chasing the brickwork to consider. The solution was a discreet riser through an existing service void, Cat6 to four desks plus two ceiling-mounted access points, all terminated to a small wall-mounted twelve-port patch panel in the existing kit cupboard alongside the router. Every cable Fluke-tested, every port labelled, a printed cert report handed over with the keys. They moved staff up over a weekend and were trading on the Monday morning without a hiccup.

A house refurb in Stoke Newington

A family home in N16 having a full back-to-brick refurbishment, three storeys plus loft and basement, with the walls open before plasterboard. This is the dream scenario from a cabling perspective. I worked off the architect's drawings and put in Cat6 to every room — two points to the kitchen-diner, two to each bedroom (one for TV, one spare), four to the home office, plus access-point drops to ceiling roses on three floors. Everything ran back to a fifteen-rack-unit cabinet in the basement utility next to the consumer unit, with a managed switch and PoE for the access points. Total of just over forty drops. Full Fluke certification report produced; the family had clean wired gigabit everywhere from day one of moving back in.

A small dental practice in Wandsworth

Dental practice in SW18 with three surgeries, a reception desk and a small server room. The existing wiring was a tangle of older Cat5 added by various people over the years, none of it tested, terminations of mixed quality. I retrofitted the practice over a weekend — new Cat6a backbone between rooms, new patch panels in a small wall cabinet, new outlets behind each surgery with discreet trunking where the walls couldn't be opened, and full PoE for the IP phones and entry-system cameras. Fluke-certified to Cat6a class EA standard. The practice was running on the new cabling at 7am Monday morning without a missed appointment.

What's included with a typical cabling job

1. An initial site visit to walk the routes, agree the outlet positions and identify any awkward sections.
2. A written quotation by phone or email setting out the scope, the cabinet layout and the certification standard.
3. Supply of all cable, faceplates, modules, patch panels and patch leads at trade pricing.
4. Cable pulled cleanly through joists, voids, risers and where unavoidable chased into plaster.
5. Terminations on each end using insulation-displacement tooling, not crimped plugs at faceplate ends.
6. Patch panel labelled and documented, switch ports patched to a logical layout.
7. Fluke DTX/DSX certification of every link, with a printed report handed over.
8. Five-year workmanship guarantee on top of any manufacturer warranty.

Where cabling lives in a finished London property

The single biggest difference between a professional install and a home job is what you don't see. A good run disappears completely: through the ceiling void above the upstairs landing, down behind the existing skirting on the inside of the wall, through a tiny hole drilled into the back of a single-gang flush-mount box, terminated on a neat faceplate that sits flush with the plaster. The cable is rated for in-wall use, the bend radius is respected at every corner, and the only thing you ever see is the white face of the wall plate. That's what a Fluke-tested Cat6 install looks like on handover. The customer's question is usually "is that it?" — and yes, that's it.

Where chasing into plaster is unavoidable I do it cleanly, with the cable in proper plastic capping or steel conduit, the chase made good with bonding plaster, and the wall sanded ready for redecoration. Bigger jobs get a snagging visit a fortnight after handover to make sure everything still works and nothing has been damaged by other trades that came in afterwards.

Common questions about cabling jobs

How long does a typical install take? A two-point retrofit in an occupied flat is usually half a day. A six-to-eight-point install during a refurbishment is a full day, sometimes spread across two visits to coincide with first and second fix. A larger commercial cabling job with twenty or thirty points runs across two or three days and is normally planned around the trading schedule of the business.

Will you make a mess? No more than I have to, and what I do make I clean up. Drilling through joists and chasing into plaster makes dust regardless of who's doing it; I bring proper dust sheets, vacuum at source, and leave the rooms cleaner than I found them at the end of each day. For sensitive jobs — a working office, a home with small children — I'll plan disruptive sections for times when they cause the least inconvenience.

Can you work with other trades? Yes, and I do regularly. Most refurbishment cabling work happens hand-in-hand with electricians, builders, plumbers and decorators. I'll coordinate around their schedule and ask for the same in return.

Ring 020 3633 1131. Advice freely given.