Introduction

You finish a nice bathroom refit, the tiling sings, the client’s happy… then the inspection flags missing bonding or no 30 mA RCD. Job stalls, confidence dips, you’re back for free. Sound familiar? This guide tackles the bathroom bonding problem head-on—what goes wrong, why it matters for safety and compliance, and field-proven ways to fix and prevent it. We’ll cover practical diagnostics, simple decision trees (bond or not?), and clean documentation that keeps you protected. No fluff—just the checks, standards and steps that get you a pass first time.

Table of Contents

• Key Takeaways
• The Problem: Bathroom Bonding That Bites Back
• Diagnose First: A Rapid Survey That Catches Issues
• Fixes That Work: Three Common Scenarios
• Proposals And Client Clarity: Avoid Surprises
• Prevention: Build It So You Never Revisit
• Frequently Asked Questions
• Conclusion

Key Takeaways

• In UK practice, bathroom circuits are commonly protected by 30 mA RCDs; with modern plastic plumbing and compliant disconnection times, supplementary bonding is often not required.
• A structured prestart survey (20–30 minutes) typically saves 2–3 hours of rework and callbacks later.
• Zones matter: Zone 0 is inside the bath/shower, Zone 1 is above to around 2.25 m, and Zone 2 extends roughly 600 mm horizontally—equipment selection and IP ratings follow these.
• Contractors often report that clear proposal notes with photos reduce back‑and‑forth by about half and speed approvals.

The Problem: Bathroom Bonding That Bites Back

Many contractors find bathroom upgrades disturb the original earthing and bonding conditions without anyone realising. Swap copper for plastic? You may remove an extraneous-conductive-part. Fit a new towel rail on an older circuit with no RCD? You may now require supplementary bonding—or a consumer unit upgrade—or both. Failures typically surface at inspection or, worse, post‑handover.

Why It Matters

• Safety: Bonding and RCDs limit touch voltage and disconnection time during faults.
• Compliance: UK jobs should follow BS 7671 (18th Edition, as amended) and Building Regulations Part P. Bathrooms are special locations; the bar is higher.
• Cost: Callbacks eat days, not hours. It’s common for teams to lose a half‑day chasing fix‑ups that a 30‑minute survey would have flagged.

The Usual Traps

• Metal pipework partially replaced with plastic breaks continuity paths—creating confusion about whether items are extraneous.
• No 30 mA RCD protection for circuits supplying bathroom equipment.
• Accessories placed in the wrong zone or with the wrong IP rating.
• Old “bond everything” habits applied where it’s no longer required—or the opposite: removing necessary bonds.

Diagnose First: A Rapid Survey That Catches Issues

Do this before you price or start. It’s quick and it pays for itself.

Step‑By‑Step Survey (20–30 Minutes)

1. Confirm the Main Earthing Terminal (MET) and main protective bonding to incoming services (water/gas) are present and suitably sized.
2. Identify all circuits entering the bathroom (lighting, towel rail, shower, fan, mirror demister, socket outside zones, underfloor heating). Confirm presence of CPCs.
3. Check RCD/RCBO coverage. In general, bathroom circuits are 30 mA RCD‑protected in modern UK practice.
4. Map the zones:
   • Zone 0: inside the bath/shower.
   • Zone 1: above the bath/shower up to around 2.25 m.
   • Zone 2: extends roughly 600 mm horizontally beyond Zone 1.
5. Identify extraneous‑conductive‑parts (incoming metal services entering from outside, structural steel if accessible). Plastic sections often mean the item is not extraneous.
6. Note any metalwork (towel rails, metal baths, exposed pipe tails) and whether they’re connected to CPCs.
7. Photograph everything you’ll rely on (clamps, RCD labels, CU, service entries, pipe materials) for your record and client clarity.

What You Decide From the Survey

• If all bathroom circuits have 30 mA RCDs and there are no extraneous‑conductive‑parts, supplementary bonding is often not required.
• If any circuit lacks RCD protection, decide: add RCD/RCBO or install supplementary bonding to bring the location up to scratch.
• If metal services are genuinely extraneous and present in the bathroom, supplementary bonding between exposed‑ and extraneous‑parts may be required.

Fixes That Work: Three Common Scenarios

Scenario 1: Mixed Plastic/Copper Plumbing, New Electric Towel Rail

Problem

You’ve introduced an exposed‑conductive‑part (the rail), but copper‑to‑plastic transitions mean the pipework is no longer extraneous. The old “bond all pipes” approach may not apply.

Solution

• Confirm RCD protection at 30 mA for the rail’s circuit.
• If the rail is on a circuit with a CPC and the location meets disconnection requirements, supplementary bonding is commonly not required.
• If RCD is absent or uncertain, either add RCD/RCBO protection or install supplementary bonding between the rail and any true extraneous‑conductive‑parts present.

Example

A small flat refit: survey shows plastic rising main with copper tails in the bathroom. RCBO present for the towel rail circuit. No extraneous parts identified in the location. Result: no supplementary bonding needed, neat CPC connection to the rail via a fused spur, and a pass at inspection.

Scenario 2: Lovely New Bathroom, But Lighting Circuit Has No RCD

Problem

Older lighting circuit with no 30 mA RCD. You’ve fitted a metal luminaire and mirror heater.

Solution

• Prefer: fit an RCBO for the lighting circuit or provide RCD protection upstream.
• Alternative: install supplementary bonding linking exposed‑conductive‑parts to extraneous‑conductive‑parts present within the location.

Example

Two‑storey house: consumer unit had MCBs only. Contractor added an RCBO for lights. With RCD protection in place and plastic cold feed, supplementary bonding wasn’t required; inspection cleared first time. Time saved versus retro‑bonding: commonly 1–2 hours.

Scenario 3: SELV Fan and Demister, Mostly Plastic Services

Problem

Client expects “bonding wires everywhere”. You know with SELV and plastic services, it may be unnecessary and untidy.

Solution

• Use SELV equipment where appropriate (transformer outside zones). Confirm 30 mA RCD protection for any 230 V circuits present.
• Confirm no extraneous‑conductive‑parts are in the bathroom.
• Document the reasoning: RCD coverage, SELV, plastic services, no extraneous parts.

Example

Compact ensuite: SELV fan in Zone 1, mirror demister via fused spur outside zones, plastic hot/cold feeds, UFH on RCBO. Contractor documented photos and circuit list. Inspector agreed no supplementary bonding required. Contractors often report that this level of clarity halves the back‑and‑forth with clients and inspectors.

Quick Fault‑to‑Fix Reference

Proposals And Client Clarity: Avoid Surprises

You can do the technical side right and still suffer delays if the client doesn’t understand why you’re adding an RCBO or refusing a socket near the bath. Clear proposals fix that.

What To Explain (Briefly, In Plain English)

• “Bathrooms are special locations. We ensure 30 mA RCD protection and correct IP ratings in the splash zones.”
• “Because your pipework is plastic, extra bonding isn’t required here. That’s safer and tidier.”
• “If we find a true extraneous metal part, we’ll bond it to keep touch voltages safe.”

How To Make It Effortless

• Capture site notes by voice and photos, then turn them into a clean proposal with assumptions and safety notes. Tools like Donizo let you speak the details on site—voice, text and photos—and generate a professional proposal PDF fast.
• Share via email with client portal access so clients can read and sign digitally. Donizo’s e‑signature makes acceptance legally binding.
• When the client signs, convert the accepted proposal to an invoice in one click and keep payment status tracked without re‑typing.

Contractors often report that this clarity reduces queries and speeds agreement by a day or more on small jobs.

Prevention: Build It So You Never Revisit

First‑Fix Standards That Stick

• Mark out Zones 0/1/2 on the wall at survey so fixings and points land correctly.
• Plan RCD/RCBO coverage at the quote stage—no surprises late on.
• Choose SELV for fans or mirrors in tighter bathrooms; keep transformers outside the zones.
• If supplementary bonding is required, run a neat, protected conductor (commonly 4 mm² when separate) with accessible clamps in dry locations.

Testing And Records

• Test RCD trip at commissioning; record circuit IDs serving the bathroom.
• Photograph bonding clamps, service entries and the CU. Store with your job file.
• Provide the client with a short “what we did and why” note—this often prevents future trades from removing safety measures.

In general, teams that bake this into their method find bathroom callbacks drop significantly, and handovers become routine rather than stressful.

Frequently Asked Questions

Do I Still Need Supplementary Bonding In UK Bathrooms?

Often not—provided all circuits in the bathroom have 30 mA RCD protection, disconnection times are compliant, and there are no extraneous‑conductive‑parts within the location. If you do have true extraneous parts (for example, incoming metal services) and you can’t meet the protective measures otherwise, supplementary bonding may be required. Always verify against the current BS 7671 and local Building Control expectations.

What Size Bonding Conductor Should I Use If It’s Required?

Common practice is 4 mm² for a separate supplementary bonding conductor, or 2.5 mm² where the conductor is in the same sheath and mechanically protected. Check BS 7671 for your specific installation method and ensure connections are accessible and durable.

Does Plastic Plumbing Mean No Bonding At All?

Plastic sections often stop an item from being extraneous, which can remove the need for supplementary bonding. But you must confirm the service path—metallic sections entering from outside can still be extraneous. Don’t assume; check at the entry point and verify continuity paths.

Will Adding An RCD Alone Fix Every Bathroom Non‑Compliance?

An RCD at 30 mA for the relevant circuits is a major safety measure, but you still need to meet zoning, IP ratings, circuit selection, and consider supplementary bonding if true extraneous parts are present. Think “RCD plus correct equipment plus correct bonding decisions.”

How Long Does A Typical Bonding/RCD Fix Take?

Small fixes—like fitting an RCBO and tidying terminations—often take 1–2 hours. Installing new supplementary bonding routes can vary from under an hour to half a day depending on access and finishes. Many contractors find a 20–30 minute prestart survey avoids the longer end of that range.

Conclusion

Bathroom bonding failures are preventable. Survey first, decide RCD vs bonding with the regs in mind, and document your reasoning. Explain zones and RCD protection in plain English, attach photos, and you’ll pass first time, keep clients calm, and protect your profit. If you want to make the admin painless, capture your site notes by voice and photos and turn them into a clear, signable proposal with Donizo. Your client signs with a legal e‑signature, and when you’re done you convert the accepted proposal to an invoice without re‑typing. Less paperwork, fewer callbacks, better days on site.