Marina Electrical Installations: BS 7671 Section 709 Guide

Yes. Marinas and similar locations are covered by Section 709, in Part 7 of BS 7671. The exclusion people confuse it with is electrical equipment on board ships, which BS 7671 does not cover (Regulation 110.2(d)); offshore installations are excluded by Regulation 110.2(e).

Section 709 is itself narrow. Regulation 709.1 states that its particular requirements apply only to circuits intended to supply pleasure craft or houseboats. They do not apply to the internal electrical installation of a pleasure craft — for those, see BS EN 60092-507 — and they do not apply to houseboats supplied directly from the public network. Everything else on the site is ordinary BS 7671 work.

The figures you came for

The six numbers that decide most marina design and inspection questions.

Why marinas get their own section

Regulation 709.512.2 spells out what Section 709 is guarding against: corrosive elements, movement of structures, mechanical damage, the presence of flammable fuel, and an increased risk of electric shock caused by the presence of water, reduction in body resistance, and contact of the body with Earth potential. Three practical consequences follow.

Section 709 of BS 7671:2018+A4:2026 applies to installations in marinas and similar locations for the supply to pleasure craft and houseboats. Use this as your on-site checklist.

These requirements sit on top of the rest of BS 7671. Section 700 puts it plainly: the particular requirements of each Part 7 section supplement or modify the general requirements, and the absence of any reference excluding a part, chapter, section or regulation means the corresponding general regulation still applies.

One A4:2026 housekeeping point worth knowing if you are working from an older copy: Figures 709.1 and 709.2 were deleted, and the connection arrangements are now shown in Figures A709.1 to A709.4.

The earthing arrangement is the most consequential decision in a marina design, and the rule is narrower than it is often described. BS 7671 does not say "TT is mandatory". It says, at Regulation 709.411.4, that the ESQCR prohibit the connection of a PME earthing facility to any metalwork in a boat — and at Regulation 709.553.1.14, that socket-outlet protective conductors shall not be connected to a PME earthing facility.

The hazard behind those two regulations is the broken PEN conductor. In a PME (TN-C-S) system the DNO's combined neutral and earth conductor provides the earth reference. If it breaks, neutral current finds another route to earth — and at a marina that route runs through the water. That is what puts voltage into the water around the berths.

Three compliant ways to supply a berth

The on-shore parts of the site — office, workshop, chandlery — may stay on the PME supply. Regulation 709.411.4 expressly says the prohibition does not preclude the use of a PME earthing facility as the means of earthing for other purposes, such as the installations of permanent buildings.

Sizing the electrode on a TT berth supply

The earth electrode resistance must be measured and recorded. Regulation 411.5.3(b) gives the criterion for an RCD used for fault protection: R_A × I_Δn must not exceed 50 V, where R_A is the sum of the resistances of the earth electrode and the protective conductor connecting it to the exposed-conductive-parts. With a 30 mA RCD that puts the arithmetic limit at about 1667 Ω — a number no one should design to. Aim far lower so the reading stays stable through dry summers and corroding connections; Regulation 411.5.3 is also met where the earth fault loop impedance satisfies the maximum values in Table 41.5.

The shore power system takes the incoming supply and distributes it to individual berths via supply pillars (also called feeder pillars or service pedestals) on the pontoons or jetty.

Socket ratings and connector standards

Regulation 709.553.1.12 sets 16 A single-phase at 200–250 V as the general default, with higher ratings where greater demands are envisaged. Regulation 709.553.1.8 fixes the connector standard by rating.

Pillars and sub-mains

The flexible cable from pillar to boat is normally the owner's. H07RN-F with matching CEE plug and connector is the standard choice. Marina operators should inspect these visually and refuse damaged cables — a cracked sheath on a trailing lead undoes every other measure on this page.

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Regulation 709.512.2 classifies equipment installed on or above a jetty, wharf, pier or pontoon against four external-influence codes — water (AD), solid foreign bodies (AE), corrosive or polluting substances (AF) and impact (AG). Socket-outlets then carry a separate, higher minimum of their own under 709.553.1.8.

Read those two rows together and the practical floor for a pontoon becomes clear: IP3X for solid bodies plus at least IPX4 for water on general equipment, and IP44 on every socket-outlet however sheltered it looks. Specifiers commonly select a single combined rating such as IP66 to satisfy both digits at the exposed end of a pontoon.

What the classifications mean on site

Regulation 709.531.2 requires that socket-outlets be protected individually by an RCD having the characteristics specified in Regulation 415.1.1 — a rated residual operating current not exceeding 30 mA. The device selected must disconnect all live conductors, including the neutral. The same requirement applies to final circuits intended for fixed connection to houseboats.

Two parts of that sentence are routinely missed on site. The first is “individually”: unlike a domestic board, RCDs may not be shared between socket-outlets. The second is the neutral — an ordinary single-pole-switched RCBO does not satisfy 709.531.2.

Keeping a PME earth away from the boat and putting an individual 30 mA RCD on every socket-outlet are the two halves of the same defence. One without the other leaves a real gap.

Section 709 is unusually specific about wiring systems. Regulation 709.521.1.4 lists what is suitable for marina distribution circuits; Regulation 709.521.1.5 then bans four of them from the pontoon itself. Getting the second list wrong is a common EICR observation.

Note the trap in row four: mineral insulated cable with an outer covering is expressly suitable for a marina distribution circuit, and expressly prohibited on or above the pontoon. Aluminium conductors are out on the pontoon regardless of termination method.

Routing, movement and drainage

BS 7671 sets no fixed interval. Regulation 652.1 requires the frequency of periodic inspection and testing to be determined having regard to the type of installation and equipment, its use and operation, the frequency and quality of maintenance, and the external influences to which it may be subjected — taking account of the results and recommendations of previous certificates and condition reports. Applied to a marina, every one of those factors points the same way, and industry practice settles on a maximum of one year.

Observations should cite Section 709 by regulation. The recurring ones on marina EICRs are shared rather than individual RCDs (709.531.2), a socket-outlet protective conductor connected to a PME earthing facility (709.553.1.14), IP integrity lost through damaged enclosures or missing glands (709.553.1.8 and 709.512.2.1.1), prohibited wiring systems on the pontoon (709.521.1.5), and corroded earth electrode connections.

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