Ultimate Guide to Earthing & Equipotential Bonding for Reliable Data Cabling Installations

Why Earthing & Bonding Still Matters in 2025

At ACCL we spend our days surrounded by copper, fibre and ever‑hungrier IT loads. Yet even the smartest Cat6a link or 40 Gbit fibre backbone can be brought to its knees by a poorly planned earth path.

BS EN 50310:2016 + A1:2020 (usually shortened to BS EN 50310:2020) is the UK‑adopted European standard that explains how to design and verify a telecommunications bonding network (TBN) inside buildings. Think of it as the electrical glue that holds together structured cabling, power distribution, surge protection and lightning protection.

In this fresh, 2025‑ready rewrite we’ll walk you through what’s changed, the key design steps, and the common pitfalls we still find on site. We’ll link you to deeper resources along the way, so grab a brew and let’s dive in.

Quick refresher: Earthing creates a low‑impedance path to safely carry fault current to ground. Equipotential bonding connects conductive parts so they stay at (roughly) the same voltage under fault conditions. Together they protect people, equipment and network performance.

What’s new in BS EN 50310:2020?

The 2020 amendment aligns the standard with:

BS 7671:2018 + A2:2022 (18th Edition IET Wiring Regulations), especially Chapter 44 on protection against transient overvoltages.
BS EN 50174‑2:2018, which tightened rules on cable separation from LV power circuits and introduced new containment materials.
BS EN 62305‑4:2019: lightning protection and surge protective device (SPD) coordination.

Key Technical Updates

Area	Pre‑2020 guidance	BS EN 50310:2020 update
Telecommunications Main Earthing Terminal (TMGB)	6 mm² minimum conductor	16 mm² Cu or equivalent; larger for >200 kA lighting risk
Earth Bonding Network (EBN) mesh size	10 × 10 m guideline	Mesh ≤5 × 5 m for high‑speed data (>10 Gbps)
Supplementary Bonding Networks	Optional	Mandatory in floor VoIP & Wi‑Fi dense offices
Measurement & verification	Visual check	Impedance test ≤0.2 Ω at every bond
Documentation	Single line diagram	Full BIM‑compatible model + maintenance schedule

The Three‑Layer Bonding Strategy

BS EN 50310 divides bonding into nested networks. We like to explain it with the image of an onion:

BBN: Building Bonding Network
Your incoming LV supply earthing conductor, structural steel and lightning protection system. Typically installed by your electrical contractor during shell‑and‑core.
EBN: Equipotential Bonding Network
Mesh of copper tapes, trays or earth bars that links plant rooms, risers and key containment routes. ACCL normally bonds containment every 20 m horizontally and each floor vertically.
SBN: Supplementary Bonding Network
Local equipotential bonding inside ICT rooms, racks and even under raised floors.

Tip: Use pre‑tinned 25 × 3 mm copper tape for riser bonding. It doubles as structural lightning down‑lead and saves space.

Designing an Earthing & Bonding Scheme: Step‑by‑Step

1. Gather the facts

Lightning risk assessment per BS EN 62305‑2.
Load schedule: servers, PoE LED lighting, CCTV, Wi‑Fi 6E APs. Higher harmonic currents demand lower impedance bonds.
Cable architecture: Are you running multi‑tenant fibre backbones? (See our guide on data cabling for multi‑tenant office buildings).

2. Choose your reference earth bar locations

Locate the Telecommunications Main Earthing Terminal (TMGB) as close as practical to the main incoming data cabling plant, usually the Main Equipment Room (MER). ACCL specifies stainless steel earth bars pre‑drilled for M10 lugs and labelled for future adds.

3. Size conductors correctly

16 mm² stranded Cu is the new minimum, but we often upsize to 25 mm² where racks exceed 10 kA fault level or to maintain equal length multiples.

4. Minimise loop impedance

Route bonding conductors in parallel with data containment, never bundled with register power cables (to stay aligned with BS EN 50174‑2 separation). Keep bends gradual; every 90° corner adds inductive reactance.

5. Plan for SPDs and MCB coordination

Modern PoE switches are vulnerable to transient over‑voltage. Coordinate Type 2 SPDs at each floor‑level distribution board and Type 3 devices at rack PDU level. See our article on cabling fire safety and over‑current protection for deeper guidance.

6. Document & test

Use BIM‑compatible single‑line diagrams exported in IFC.
Perform continuity testing: target ≤0.2 Ω between any exposed‑conductive‑part and the TMGB.
Keep results with O&M manual and schedule annual retesting. Your facilities team can book this as part of an ACCL data‑cabling audit.

Common Site Issues & How We Solve Them

Isolated racks in legacy buildings

Historic estates often have patch cabinets in closets with no local earth. We install sub‑earth bars and bond back to the EBN via spare steel conduit: quick win, minimal disruption. (See tips for heritage sites in our post on network cabling upgrades in historic buildings).

Poor segregation from power

Running Cat6a right next to 400 V armoured cable invites EMI. BS EN 50174‑2 calls for 200 mm air gap or metallic divider. We like basket tray with a snap‑on copper lid, which gives both screening and bonding.

Forgotten PoE lighting drivers

PoE luminaires are usually Class 2, but the metallic housings still need bonding if they’re part of a suspended ceiling grid. We fit bonding jumpers every 3rd tile run.

Painted steelwork

A fresh coat of intumescent paint looks great but kills conductivity. Our engineers file small coupon‑size patches and apply conductive grease before bolting earth lugs. We then spray clear lacquer for corrosion resistance.

Missing documentation

If you can’t prove the earth path, insurers may refuse downtime claims. ACCL offers digital twin asset tagging: scan a QR code on the earth bar, pull test certs instantly. Talk to our structured cabling team to learn more.

Earthing & Bonding Checklist

☐ Lightning risk assessment complete
☐ TMGB located <5 m of MER
☐ BBN, EBN, SBN routes modelled in BIM
☐ All data containment bonded every 20 m & each floor
☐ SPDs coordinated (Type 1 at service entry, Type 2 at DBs, Type 3 at racks)
☐ Continuity tested ≤0.2 Ω end‑to‑end
☐ O&M manual + maintenance plan issued

Need help ticking every box? Contact ACCL. Our NICEIC‑approved engineers are ready to assist.

Future Trends: Mesh Bonding meets Smart Buildings

Smart building platforms, digital twins and IoT sensors are turning every luminaire, HVAC damper and door into a network node. That means more PoE, more edge switches, and more paths for fault currents. Expect the next revision of BS EN 50310 to address:

Higher‑power PoE (IEEE 802.3bt): up to 90 W per port influencing conductor sizing.
DC microgrids: common earth reference between AC and 48 V DC busbars.
Active monitoring: continuous impedance sensing via inline probes and cloud dashboards.

Staying proactive with a robust bonding design today will make tomorrow’s retrofits painless.

Wrapping Up

Earthing and equipotential bonding may not be as glamorous as 800 Gig Ethernet optics, but without it your digital infrastructure is literally built on shaky ground. BS EN 50310:2020 gives a clear, modern framework. Combine it with the 18th Edition wiring regs, a dash of practical field know‑how and reliable test data, and you’ve set the foundation for decades of resilient uptime.

If you’d like us to review your current installation, perform impedance testing or design a bonding network from scratch, reach out to ACCL today.

Written by

Wayne Connors

Founder & Managing Director, ACCL

Wayne founded ACCL in 1997 and has led more than 28 years of project delivery, helping organisations design, install and modernise the network infrastructure behind reliable connectivity, office moves and refurbishments. His experience spans copper cabling, fibre backbones, data centre infrastructure, Wi-Fi, CCTV and access control. About ACCL

Add ACCL as a preferred source on GoogleTell Google you want to see more ACCL guides in Top Stories when you search. Opens Google in a new tab.

Ultimate Guide to Earthing & Equipotential Bonding