SPECIALIST INSTALLATION

Marina & Mooring Electrical Installation UK: BS 7671 Section 709

Everything electricians and marina operators need to know about shore power electrical installations — BS 7671 Section 709 requirements, galvanic corrosion protection, earth leakage monitoring, IEC 60309 connectors, 30 mA RCD protection, and annual inspection obligations.

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14 min readUpdated 2026-05-18Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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Key Takeaways

  • 1BS 7671:2018+A4:2026 Section 709 governs electrical installations in marinas and similar locations including boat harbours and yacht clubs. It applies from the origin of the shore supply to the socket outlets on the pontoons.
  • 2Shore power socket outlets must comply with IEC 60309 (BS EN 60309) — the blue 16 A or 32 A CEE connectors are the standard for marina hookups throughout the UK and Europe.
  • 3Galvanic corrosion is a critical hazard in marina installations. Stray DC currents through the water caused by mixed-metal hulls and poor bonding can destroy underwater metalwork over months. Galvanic isolators or isolation transformers are strongly recommended.
  • 4Earth leakage monitoring (ELM) systems are required by Section 709 to detect fault currents before they reach dangerous levels. Each socket outlet supply must be monitored individually.
  • 530 mA RCD protection is required for every shore power socket outlet. Type A RCDs must be used where electronic equipment on board boats may produce pulsating DC residual currents.
  • 6The recommended periodic inspection interval for marina electrical installations is 1 year (IET Guidance Note 3). Annual inspection should include RCD testing, earth leakage monitor testing, and visual inspection of all socket outlets and cable management.
01 · Specialist Installation

BS 7671 Section 709: Marinas and Similar Locations

BS 7671:2018+A4:2026 Section 709 — Marinas and Similar Locations — is the authoritative technical standard for shore power electrical installations at UK marinas, boat harbours, inland waterway moorings, and yacht clubs. It applies to the fixed installation from the origin of the shore supply to (and including) the socket outlets mounted on pontoons and jetties.

  • Scope of Section 709 — covers the fixed electrical installation supplying shore power to boats, yachts, motorboats, and other craft moored at pontoons, berths, and jetties. It does not apply to the internal wiring of individual craft, which is governed by separate marine standards. Where Section 709 is silent, the general requirements of BS 7671 apply.
  • Specific hazards — marina installations present hazards not found in most other electrical environments: the corrosive salt and fresh water environment, floating pontoons subject to tidal movement, the risk of electric shock through conductive water (electric shock drowning), galvanic corrosion from stray DC currents, and non-expert users (boat owners) connecting and disconnecting their own shore power leads.
  • Electric shock drowning — electric shock drowning (ESD) is a potentially fatal hazard specific to aquatic environments. A voltage gradient in the water — caused by a fault current flowing from shore power through the water to earth — can cause muscular paralysis in swimmers, preventing them from reaching safety. Earth leakage monitoring and rapid RCD disconnection are the primary protective measures.

Electricians working on marina installations should hold a current BS 7671 qualification and be familiar with Section 709. The IET Guidance Note 7 (Special Locations) provides supplementary guidance on marina installations.

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02 · Specialist Installation

Shore Power Connections and Socket Outlet Units

Shore power socket outlet units (sometimes called pedestal units or power posts) are the interface between the marina's fixed installation and individual boats. Their design, rating, and installation must comply with Section 709 and the requirements for outdoor electrical equipment.

  • Individual supply per berth — each berth must be supplied through its own socket outlet unit with individual overcurrent protection and RCD protection. Sharing supply between berths is not permitted, as it prevents individual isolation and individual leakage current monitoring.
  • RCBO protection — modern marina pedestal units typically incorporate an RCBO (Residual Current Circuit Breaker with Overcurrent protection) per socket outlet, combining 30 mA RCD protection and overcurrent protection in a single device. This allows the berth supply to be isolated without affecting other berths on the same submain.
  • IP rating — socket outlet units must have a minimum IP rating of IP44. Units on exposed pontoons or tidal locations may require IP55 or higher. The pontoon environment exposes electrical equipment to salt spray, rain, wave splash, and occasional immersion — IP rating selection must reflect the actual installation conditions.
  • Corrosion resistance — pedestal enclosures must be made from materials resistant to marine corrosion. GRP (glass-reinforced plastic) and marine-grade stainless steel are standard. Standard steel enclosures will corrode rapidly in a saltwater marina environment, compromising both structural integrity and electrical safety.
03 · Specialist Installation

Galvanic Corrosion: Causes and Protection

Galvanic corrosion is one of the most significant and often underappreciated hazards in marina electrical engineering. It is caused by DC currents flowing through the water between dissimilar metals on adjacent boats connected to the same shore power earth conductor.

  • The galvanic cell — when two dissimilar metals (for example aluminium and bronze) are immersed in the same electrolyte (salt or fresh water) and electrically connected, a galvanic cell is formed. The less noble metal (aluminium) acts as the anode and corrodes. In a marina, the shore power earth conductor connecting multiple boats creates this electrical connection.
  • Galvanic isolator — a galvanic isolator (complying with BS EN 61191 or equivalent) is a DC blocking device fitted in series with the shore power earth conductor. It passes AC fault currents (essential for protective device operation) but blocks low-level DC galvanic currents. Galvanic isolators are strongly recommended for all boats connected to shore power.
  • Isolation transformer — an isolation transformer on board the boat provides complete galvanic isolation from the shore earth. The boat's AC system is referenced to a floating (unearthed) supply derived from the transformer secondary. This eliminates galvanic currents entirely but is more expensive and requires careful design to maintain shock protection.

Marina operators should advise berth holders of the galvanic corrosion risk and the protective measures available. Electricians designing or inspecting marina installations should verify that galvanic protection measures are in place and functioning correctly.

04 · Specialist Installation

Earth Leakage Monitoring Systems

Section 709 requires earth leakage monitoring (ELM) systems in marina installations. ELM systems provide continuous monitoring of residual current in shore power circuits, alerting marina staff to developing faults before they reach dangerous levels.

  • How ELM works — a current transformer fitted around the live and neutral conductors of each shore power circuit continuously measures the difference between outgoing and returning current. Any difference (residual current) indicates a fault path — either through a fault on the boat, through the water, or through a damaged cable. The ELM system triggers an alarm when the residual current exceeds the pre-set threshold (typically 10 mA or 15 mA).
  • Alarm vs. trip — the ELM system typically provides an alarm rather than automatically disconnecting the supply. This allows marina staff to investigate and advise the boat owner before disconnection. The 30 mA RCD remains the primary automatic protective device for shock protection.
  • Central monitoring — in modern marinas, ELM signals are aggregated to a central marina management system, allowing marina staff to identify which berth has a developing fault and respond quickly. Systems can send alerts by email or SMS to the marina manager.
  • Testing at inspection — ELM systems must be tested at every periodic inspection. Testing involves injecting a known residual current into the monitoring circuit and verifying the alarm operates at or below the pre-set threshold. Test results should be recorded in the inspection report.
05 · Specialist Installation

IEC 60309 CEE Connectors for Marina Shore Power

IEC 60309 (BS EN 60309) connectors are the standard for marina shore power throughout the UK and Europe. Their weatherproof construction, earth-first engagement, and colour-coded voltage identification make them well suited to the demanding marina environment.

  • 16 A blue single-phase — the standard connector for leisure craft and small boats. Provides a nominal 3.68 kW supply at 230 V. This is the same connector used at caravan parks, making standardised EHU (electric hookup) cables compatible between marinas and caravan sites.
  • 32 A blue single-phase — used for larger motorboats and yachts with higher power requirements (heating, air conditioning, refrigeration). Provides up to 7.36 kW. Larger vessels may require 63 A or three-phase supplies.
  • Locking mechanism — marina-specific IEC 60309 socket outlets typically incorporate a locking collar that prevents the plug from being accidentally disconnected by a wave or the boat's movement. This feature is not required by the standard but is strongly recommended for marina use.

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06 · Specialist Installation

RCD Requirements for Marina Installations

RCD protection is mandatory for every shore power socket outlet in a marina installation under Section 709. The aquatic environment makes rapid disconnection of fault currents more critical here than in almost any other electrical installation.

  • 30 mA individual RCD per socket — Regulation 709.411.3.3 requires each socket outlet to be individually protected by a 30 mA RCD. A single RCD protecting multiple berths is not acceptable under Section 709, as a fault at one berth must not disconnect other berths.
  • Type A RCDs — boats with electronic equipment on board (inverter-chargers, engine management, electronic instrumentation) can produce pulsating DC residual currents that Type AC RCDs cannot detect. Type A RCDs detect both sinusoidal and pulsating DC residual currents. All marina installations should use Type A RCDs as standard.
  • Disconnection time — RCDs must operate within the time limits specified in BS 7671 Table 41.1. For 30 mA RCDs protecting socket outlet circuits, the maximum disconnection time at 5× IΔn (150 mA) is 40 ms. Annual RCD testing must verify these operating times using a calibrated RCD tester.
07 · Specialist Installation

Earthing Arrangements at Marinas

Earthing at marinas is complex and presents unique challenges not found in other installations. The interaction between the shore earth, the water, galvanic currents, and protective earth conductors on individual boats requires careful engineering.

  • TT vs. TN systems — many marinas are TT earthed, particularly where the distribution network does not provide a reliable PME (protective multiple earthing) earth at the marina origin. TT earthing requires earth electrode resistance testing at commissioning and at every annual inspection. The earth electrode must be positioned to minimise the risk of step voltages in areas accessible to marina users.
  • PME prohibition — Section 709 prohibits the use of PME (TN-C-S) earthing for shore power socket outlets at marinas. This is because the PME combined neutral-earth conductor, if broken, can result in dangerous voltages on metalwork accessible to users in or near the water. A local TT earth arrangement or an isolating transformer must be used.
  • Structural metalwork bonding — all metallic structural elements of the marina — steel pontoon frames, handrails, ladders, berthing cleats — must be assessed for bonding requirements. Where metalwork is accessible to persons who may simultaneously contact the water, bonding is required to equalise potentials and prevent electric shock.
08 · Specialist Installation

For Electricians: Marina Inspection and Certification

Marina electrical work is a specialist area with significant life-safety implications. Electricians who develop expertise in Section 709 installations can build valuable relationships with marina operators, who need qualified annual inspections and ongoing maintenance support.

Complete EICRs On Site

Use the Elec-Mate EICR app to complete marina inspection reports berth-by-berth on your phone. Record RCD test results, earth leakage monitor test results, and earth electrode resistance measurements in the schedule of test results. Generate the PDF report before leaving the site.

Annual Contracts with Marina Operators

Annual inspection is the recommended interval for marina installations. Use the quoting app to offer multi-year maintenance packages to marina operators, covering annual inspection, RCD testing, and ELM system testing. A marina with 50+ berths represents a substantial recurring revenue opportunity.

Marina inspection work made simple with Elec-Mate

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