What is the difference between BS 7909 and BS 7671?

BS 7671 (the IET Wiring Regulations, 18th Edition) is the national standard for electrical installations in the UK and applies to all electrical installations, including temporary ones. BS 7909 is a separate Code of Practice that specifically addresses temporary electrical systems for entertainment and related purposes — including outdoor events, concerts, festivals, exhibitions, and temporary structures. BS 7909 supplements BS 7671 with additional requirements that are specific to temporary installations, such as environmental protection (IP ratings for outdoor use), cable management in public areas, generator supply requirements, and the particular risks associated with temporary structures and outdoor events. Where BS 7909 applies, BS 7671 still forms the foundation — BS 7909 adds to it but does not replace it. For construction site temporary installations that are not entertainment-related, BS 7671 Section 704 (Construction and demolition site installations) applies directly.

Does a temporary installation need an electrical certificate?

Yes. Temporary installations must be inspected and tested in accordance with BS 7671, and the results must be recorded on the appropriate certificate. For a new temporary installation, an Electrical Installation Certificate (EIC) must be issued, confirming that the installation has been designed, constructed, inspected, and tested in accordance with BS 7671. For periodic re-testing (which should occur at least every 3 months on construction sites and before each event for entertainment installations), an Electrical Installation Condition Report (EICR) should be issued. Minor additions or alterations to an existing temporary installation may be covered by a Minor Electrical Installation Works Certificate (MEIWC). All certificates must be completed by a competent person and retained as part of the project documentation.

What earthing system is used for temporary installations?

The earthing system for a temporary installation depends on the supply source. If the temporary installation is supplied from the public distribution network (mains supply), the earthing arrangement will typically follow the DNO supply — TN-S, TN-C-S (PME), or TT. However, BS 7909 recommends against relying on a PME (TN-C-S) earth for temporary installations in outdoor or high-risk environments because a loss of the PEN conductor could put exposed metalwork at mains potential. In these cases, a TT earthing arrangement with earth electrodes is preferred. If the supply is from a generator, the earthing system will typically be either TN-S (with the generator star point earthed and a separate earth conductor) or IT (unearthed, with an insulation monitoring device). For outdoor events and festival installations, TT earthing with driven earth electrodes is the most common and safest arrangement. The earth electrode resistance must be tested and verified before the installation is energised.

How often should a temporary installation be inspected?

The inspection frequency depends on the type of temporary installation and the environment. BS 7671 Regulation 652 requires the interval to be determined by a competent person having regard to the type of installation, its use, and the external influences it is subjected to. Established industry practice (reflected in IET Guidance Note 3 and HSE guidance) is that construction site temporary installations are inspected and tested at intervals not exceeding 3 months. For entertainment and events, BS 7909 recommends inspection and testing before each event or season of use. If the installation remains in place for an extended period — for example, a long-running construction project — periodic inspection should continue at 3-monthly intervals throughout. Between formal inspections, visual checks should be carried out daily or weekly by a competent person — looking for cable damage, loose connections, water ingress, and signs of overheating. Any defects found during visual checks must be reported and rectified before the installation is used.

What IP rating is required for temporary outdoor electrical equipment?

For outdoor temporary installations, all electrical equipment must be protected against water ingress and dust to a level appropriate for the environment. The minimum IP rating for outdoor distribution equipment is typically IP44 (protected against splashing water from all directions and objects greater than 1mm). For equipment that may be exposed to heavy rain, hose-down cleaning, or water jets, IP55 or IP65 is recommended. Socket outlets used outdoors should be IP44 minimum when in use (with the flap closed over the plug). Equipment at ground level in areas prone to flooding or standing water should be IP67 (protected against temporary immersion). All connections, junction boxes, and cable terminations must be made using appropriate IP-rated enclosures — never use domestic-grade junction boxes or connector strips in outdoor temporary installations. The IP rating should be clearly marked on all equipment.

Can I use a domestic consumer unit for a temporary installation?

No. Domestic consumer units (metal or plastic, designed for permanent fixed installation in dry indoor environments) are not suitable for temporary installations on construction sites or at outdoor events. Temporary installations require distribution equipment that is designed for the environment — typically industrial-grade distribution boards in IP44 or higher enclosures, with BS 4343 (IEC 60309) industrial plugs and sockets. The distribution boards must be mechanically robust (able to withstand the knocks and impacts of a construction or event environment), environmentally protected (IP-rated for outdoor or wet conditions), and electrically appropriate (with adequate fault ratings, RCD protection, and cable entries). Pre-assembled temporary distribution boards ("panel boards" or "distro boards") specifically designed for construction or event use are widely available and should always be used in preference to domestic equipment.

TECHNICAL GUIDE

Temporary Installations: BS 7909, Events, and Construction Sites

Temporary electrical installations demand the same rigour as permanent ones — and often more. From construction site supplies to festival power systems, this guide covers supply design, earthing, RCD protection, testing, and the documentation that proves compliance.

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12 min readUpdated 2026-06-10Andrew 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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What is BS 7909 and how does it relate to BS 7671?

BS 7909 is the UK Code of Practice for temporary electrical systems for entertainment and related purposes — outdoor events, concerts, festivals, exhibitions and temporary structures. It supplements BS 7671 (the IET Wiring Regulations) rather than replacing it: every temporary installation must still meet BS 7671 as the baseline. Temporary installations on construction and demolition sites are instead covered directly by BS 7671 Section 704.

Section 704 mandates that a PME (TN-C-S) earthing facility shall not be used on a construction site unless all extraneous-conductive-parts are reliably bonded (Reg 704.411.3.1), and that socket-outlets and hand-held equipment up to 32 A are protected by reduced low voltage, automatic disconnection with a 30 mA RCD, electrical separation or SELV/PELV (Reg 704.410.3.10).

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Key Takeaways

1BS 7909 is the Code of Practice for temporary electrical systems for entertainment and related purposes — it supplements BS 7671 with requirements specific to temporary installations.
2Temporary installations must have an effective earthing system, appropriate RCD protection (30mA for socket outlets), and be designed to withstand the environmental conditions on site.
3All temporary installations must be inspected and tested before first use and at regular intervals thereafter — typically every 3 months on construction sites.
4Comprehensive documentation is required including single-line diagrams, test certificates, risk assessments, and method statements for the installation.
5Elec-Mate generates electrical installation certificates, risk assessments, and RAMS documents for temporary installations — saving hours of paperwork per project.
6RCD type selection matters: Type A covers pulsating DC; Type F covers composite/mixed-frequency loads (variable-speed drives); Type B covers smooth DC components — Type AC (BS 7671 Reg 531.3.3) may now only serve fixed equipment where the load contains no DC components, so it cannot be the default on modern loads.
7Section 704 does not apply to administrative locations on construction sites (offices, canteens, welfare facilities) — those areas are subject to the general requirements of BS 7671 only (Reg 704.1.1).
8On construction and demolition sites a PME (TN-C-S) earthing facility must not be used unless every extraneous-conductive-part is reliably bonded to the main earthing terminal (BS 7671 Reg 704.411.3.1) — in practice TT with an earth electrode is the default.

01 · Technical Guide

What Does BS 7909 Cover?

BS 7909 is the British Standard Code of Practice for the design and installation of temporary electrical systems for entertainment and related purposes. It was developed to address the specific requirements of temporary electrical installations that go beyond what BS 7671 covers for permanent installations.

Entertainment and events: Concerts, festivals, theatres, outdoor shows, exhibitions, conferences, and any temporary venue where electrical systems are installed for a limited period.
Temporary structures: Marquees, temporary stages, grandstands, hospitality areas, and any structure erected for a temporary purpose that requires an electrical supply.
Construction sites: While BS 7671 Section 704 specifically covers construction and demolition site installations, the principles in BS 7909 regarding temporary supply design, environmental protection, and cable management are also applicable.
Generator-supplied installations: BS 7909 provides detailed guidance on using generators as supply sources, including earthing arrangements, voltage regulation, and fault protection for generator-fed systems.

BS 7909 does not replace BS 7671 — it supplements it. Every temporary installation must comply with BS 7671 as the baseline, with BS 7909 adding additional requirements where the temporary nature of the installation creates specific risks (such as cable damage from foot traffic, water ingress from outdoor conditions, or the need for rapid assembly and disassembly).

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02 · Technical Guide

Temporary Supply Design

Designing a temporary electrical supply requires careful planning. Unlike a permanent installation where the supply is established and the installation is built around it, a temporary installation often starts with the question: "Where is the power coming from, and how much do we need?"

Supply sources: Temporary installations can be supplied from the public mains (via a temporary builder's supply from the DNO), a portable generator, or a combination of both. For large events, multiple generators may be used in parallel with automatic changeover from mains.
Load assessment: Calculate the maximum demand for the temporary installation, applying diversity factors where appropriate. Include all loads: lighting, power tools (or stage equipment for events), heating, welfare facilities, and any specialist equipment. Size the supply, main cables, and protection devices to handle the maximum demand with adequate headroom.
Distribution layout: Plan the distribution board layout to minimise cable runs and provide power where it is needed. Use sub-distribution boards to bring power to different areas of the site or event. Each distribution board must have its own main isolator, RCD protection, and circuit protection devices.
Cable selection: Cables for temporary installations must be suitable for the environment. Use SWA (Steel Wire Armoured) or equivalent for buried or semi-permanent runs. Use H07RN-F (heavy-duty rubber-sheathed flexible cable) for above-ground runs that may be subject to foot traffic or mechanical damage. All cables must be adequately rated for the current they will carry, taking into account cable sizing factors including ambient temperature and grouping.

Minimum IP ratings by environment

Indicative guidance for distribution equipment, enclosures and connectors. Select for the worst conditions the equipment will actually see (rain, hose-down, ground water), not the conditions on a dry commissioning day.

Location	Minimum IP	Protects against
Indoor / under cover, dry	IP2X – IP4X	Finger/solid-object contact; no specific water protection
Outdoor, general exposure	IP44	Solid objects >1mm and splashing water from any direction
Heavy rain / hose-down cleaning	IP55 – IP65	Dust ingress and low-pressure water jets from any direction
Ground level, flood / standing water risk	IP67	Dust-tight and temporary immersion (up to 1m for 30 min)

03 · Technical Guide

Earthing and Bonding for Temporary Installations

Earthing is the single most critical safety element of a temporary installation. Without effective earthing, protective devices cannot operate in the event of a fault, and exposed metalwork can become live — creating a lethal shock hazard.

TT earthing is preferred for outdoor temporary installations. BS 7909 recommends against relying on PME (TN-C-S) earthing for temporary installations in outdoor or high-risk environments. A loss of the PEN conductor in a PME system would put all exposed metalwork at mains potential — in an outdoor environment with wet conditions and metallic structures, this is extremely dangerous.
Earth electrodes: For TT earthing, driven earth electrodes (copper clad steel rods) are used to establish an earth connection. The electrode resistance must be measured and verified — a value of 200 ohms or less is typically required to ensure RCD operation within the required disconnection time. Multiple electrodes may be needed to achieve this in poor soil conditions.
Bonding: All extraneous conductive parts within the temporary installation must be bonded to the main earthing terminal. This includes metal structures (scaffolding, staging, trusses), metallic water pipes, and any other metalwork that could introduce an earth potential. Main protective bonding conductors are sized per BS 7671 Reg 544.1.1 — not less than half the cross-sectional area of the earthing conductor, with an absolute minimum of 6mm² copper (or 10mm² copper where PME supply conditions apply, per Table 54.8). Supplementary bonding conductors (Reg 544.2) must be at least 2.5mm² copper where mechanically protected, or 4mm² copper where they are not.

Earthing systems for temporary supplies

On construction and demolition sites, a PME (TN-C-S) earthing facility must not be used unless every extraneous-conductive-part is reliably bonded to the main earthing terminal (BS 7671 Reg 704.411.3.1) — in practice this is very difficult to maintain, so TT is the default.

System	Source	Suitability for temporary work
TT	Mains or generator with earth electrode	Preferred outdoors and on sites. Fault protection relies on RCDs; electrode resistance must be measured and stable.
TN-S	DNO TN-S, or generator with earthed star point + separate PE	Acceptable where a sound, dedicated earth conductor is available all the way back to the source.
TN-C-S (PME)	DNO combined PEN	Restricted on sites (Reg 704.411.3.1); a lost PEN puts metalwork at mains potential — avoid outdoors.
IT	Unearthed generator	Continues to run on a first fault, but requires an insulation monitoring device to alarm before a second fault occurs.

For generator-supplied installations, the earthing arrangement depends on the generator configuration. A generator with an earthed star point typically operates as a TN-S system. An unearthed generator operates as an IT system, which requires an insulation monitoring device to detect first faults. The earthing arrangement must be documented on the single-line diagram and verified by testing before the installation is energised.

04 · Technical Guide

Protection and Overcurrent Devices

Temporary installations require the same level of overcurrent and fault protection as permanent installations — and often more, because the environmental conditions are harsher and the risk of damage is higher.

RCD protection: Socket-outlets with a rated current up to 32A require additional protection by a 30mA RCD (BS 7671 Reg 411.3.3), with limited exceptions permitted by that regulation. For TT earthing systems, RCD protection is essential for fault protection: earth fault loop impedance via driven electrodes is typically too high for overcurrent devices alone to achieve the required disconnection times, so RCDs are the primary means of achieving disconnection. The RCD type must be matched to the load it protects (BS 7671 Reg 531.3.3) — see the table below.
MCBs and RCBOs: Each circuit must be protected by an appropriately rated MCB or RCBO. The protective device must be selected to provide both overload protection and short-circuit protection. The breaking capacity of the protective device must be equal to or greater than the prospective fault current at the point of installation.
Discrimination: Where multiple levels of RCD protection are used (for example, a 100mA time-delayed RCD at the main board and 30mA RCDs at sub-boards), discrimination must be achieved to ensure that a fault on one circuit only trips the nearest RCD, not the upstream one.

RCD type selection (Reg 531.3.3)

Choose the lowest type that fully covers the residual-current waveform the load can produce. Type AC may only serve fixed equipment with no DC content.

Type	Detects	Typical temporary-installation loads
AC	Sinusoidal AC residual current only	Fixed resistive loads with no DC content only (e.g. simple heaters, filament lamps). Not suitable as a default for modern electronics.
A	AC + pulsating DC residual current	General socket outlets, single-phase tools, most LED and switch-mode loads — the practical minimum for modern equipment.
F	As Type A + composite/mixed-frequency residual currents	Single-phase variable-speed drives, dimmers and stage equipment producing mixed-frequency residual currents.
B	As Type F + smooth DC residual currents (incl. 3-phase rectified)	Three-phase drives, EV charge points and other equipment that can produce smooth DC fault current.

The type and rating of RCD must be carefully selected for the loads being protected. Modern entertainment lighting and stage equipment often contain electronic drivers that produce pulsating DC or composite fault currents — a standard Type AC RCD will not detect these. Use Type A as a minimum for most modern equipment; Type F where variable-speed drives or mixed-frequency loads are present; and Type B where smooth DC components exist (Reg 531.3.3).

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05 · Technical Guide

Testing and Verification of Temporary Installations

Every temporary installation must be inspected and tested before it is energised for the first time. The testing regime is the same as for a permanent installation under BS 7671 Chapter 64 (Initial Verification), with additional visual checks for the temporary-specific risks.

Visual inspection: Check all cables for damage; verify all connections are tight and properly terminated; confirm IP ratings of enclosures are appropriate for the environment; check cable routing for trip hazards, water exposure, and mechanical damage risks; verify labelling of all circuits and distribution boards.
Dead tests: Continuity of protective conductors (including main and supplementary bonding); continuity of ring final circuits (if applicable); insulation resistance per Reg 643.3 (for circuits up to and including 500V, test at 500V DC with a minimum acceptable value of 1.0 MΩ — BS 7671 Table 64); polarity checks at all points.
Live tests: Earth fault loop impedance at the furthest point of each circuit (to verify disconnection times); prospective fault current at the origin; RCD testing (trip time at rated current, 5x rated current, and ramp test); voltage and frequency at the origin.
Functional tests (Reg 643.10): Verify all switching and isolation devices operate correctly; test emergency stop buttons and emergency lighting (where installed); verify that generator changeover systems operate correctly (where installed).

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06 · Technical Guide

Documentation Requirements

Temporary installations require the same documentation as permanent installations, plus additional records specific to the temporary nature of the work. For event installations under BS 7909, the documentation requirements are particularly detailed.

Single-line diagram: A schematic showing the supply source, main distribution, sub-distribution, cable types and sizes, protective devices, earthing arrangement, and all loads. This is the reference document for anyone working on or maintaining the installation.
Electrical Installation Certificate (EIC): Issued for the initial installation, confirming compliance with BS 7671. Must be completed before the installation is energised.
Schedule of test results: All dead and live test results recorded in the standard format. Must accompany the EIC.
Risk assessment and method statement (RAMS): Covering the installation, commissioning, operation, and decommissioning of the temporary electrical system. Must be completed before work begins.
Periodic inspection records: For installations that remain in place for extended periods, regular inspection and test records (EICR) at intervals not exceeding 3 months.

For entertainment events, BS 7909 also recommends a site-specific electrical safety policy, an emergency procedure document, and a handover document for the event organisers confirming that the installation is safe for use.

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07 · Technical Guide

Construction Sites vs Events: Key Differences

While the fundamental principles of temporary installation design are the same, there are important differences between construction site installations and entertainment/event installations:

Construction Sites

BS 7671 Section 704 applies directly
110V CTE reduced low voltage strongly preferred for portable tools (Reg 704.410.3.10)
3-month inspection intervals
CDM 2015 duties apply
Users are trained electricians and trades

Entertainment and Events

BS 7909 supplements BS 7671
230V and 400V commonly used for lighting rigs
Inspection before each event
Public safety is the primary concern
Users may include untrained public

Note on Section 704 scope (Reg 704.1.1): The particular requirements of Section 704 do not apply to administrative locations on construction sites — offices, cloakrooms, meeting rooms, canteens, restaurants, dormitories, and toilets are explicitly excluded. Those areas are treated as ordinary installations under the general requirements of BS 7671.

The public safety dimension of event installations cannot be overstated. On a construction site, the users of the electrical system are (or should be) trained workers who understand the risks. At an event, members of the public — including children — may come into proximity with the temporary electrical installation. This demands higher standards of cable protection, enclosure security, and signage. All accessible distribution equipment must be locked or secured to prevent public access.

Frequently Asked Questions About Temporary Installations

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Temporary Installations: BS 7909, Events, and Construction Sites

What is BS 7909 and how does it relate to BS 7671?

Key Takeaways

What Does BS 7909 Cover?

Get the BS 7671 A4:2026 Cheat Sheet — free

Temporary Supply Design

Minimum IP ratings by environment

Earthing and Bonding for Temporary Installations

Earthing systems for temporary supplies

Protection and Overcurrent Devices

RCD type selection (Reg 531.3.3)

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Testing and Verification of Temporary Installations

Complete electrical certificates on your phone

Documentation Requirements

Generate RAMS and certificates with AI

Construction Sites vs Events: Key Differences

Construction Sites

Entertainment and Events

Frequently Asked Questions About Temporary Installations

What is the difference between BS 7909 and BS 7671?

Does a temporary installation need an electrical certificate?

What earthing system is used for temporary installations?

How often should a temporary installation be inspected?

What IP rating is required for temporary outdoor electrical equipment?

Can I use a domestic consumer unit for a temporary installation?

Continue reading

Electrical Safety on Site

Earthing Arrangements

RCD Testing Guide

Risk Assessment for Electricians

BS 7671 18th Edition Guide

Construction Site Electrical Safety

What electricians say

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Certificates and RAMS for Temporary Installations