Section 705 of BS 7671 covers agricultural and horticultural premises, and it is one of the strictest special locations in the book. Two facts set the tone: every circuit needs RCD protection, with 300 mA the ceiling for fire protection on anything that is not a socket circuit, and any metalwork livestock can touch must be tied into supplementary equipotential bonding. Add ammonia, wash-down, dust, rodents and animals whose hooves stand in wet slurry, and a farm punishes any installation that was treated like a domestic job. This guide walks through what Section 705 actually asks for, how to test it, and how to code what you find on an EICR.
- Section 705 applies to fixed installations indoors and outdoors on agricultural and horticultural premises, and to the parts of a dwelling on the farm that are electrically connected to them.
- RCDs everywhere: 30 mA for socket-outlet circuits up to 32 A, 100 mA or less for socket circuits above 32 A, 300 mA or less on all other circuits for fire protection.
- Supplementary bonding is mandatory in livestock areas, and floor reinforcement or metal grids in the floor must be connected to it.
- Equipment needs IP44 minimum, more where wash-down or ammonia is present, and must be out of reach of animals or mechanically protected.
- Radiant heaters for livestock must be fixed at least 0.5 m from animals and combustibles.
- The installation must come with a plan, single-line diagram and bonding diagram (705.514.9.3).
- Test with the animals in mind: bonding continuity to floor grids, RCD trip times at 300 mA as well as 30 mA, and earth electrode resistance on TT systems.
Where does Section 705 apply, and where does it stop?
Regulation 705.1 scopes the section to fixed electrical installations, indoors and outdoors, in agricultural and horticultural premises. That means cattle sheds, milking parlours, pig and poultry units, stables, grain stores, greenhouses, polytunnels with fixed supplies, and the yards and outbuildings around them. It also brings in the farmhouse and any other dwelling on the site where they are electrically connected to the agricultural installation, which is common because the farm supply often lands in the house first.
It does not cover the rooms where livestock are not kept and where ordinary Part 4 and Part 5 rules apply on their own, such as a farm office that is separately supplied, and it does not deal with the electrical equipment of machinery, which is covered by product standards. The judgement call is usually the mixed building: a workshop that opens into a stable, or a feed store beside the parlour. If animals can get in, or the environment is the same, treat it as a 705 location.
Section 705 sits on top of the general rules, not instead of them. Section 522 on external influences, Chapter 41 on shock protection, Chapter 42 on fire, and Section 544 on bonding all still apply. If you are also running a supply to a cottage, a caravan for a seasonal worker, or a shop, Sections 708 and 709 in the caravan and marina guide at Caravan Parks and Marinas: Sections 708 and 709 Explained and the outbuilding supply guide at Outbuilding and Garden Supply: SWA, TT or PME Earth? cover the crossover.
What RCD protection does Section 705 require?
This is the part most often got wrong on farms wired before 2008, and the table below sets out the current position under BS 7671:2018+A4:2026.
| Circuit type | Maximum RCD rating | Regulation | Purpose |
|---|---|---|---|
| Final circuits supplying socket-outlets rated up to 32 A | 30 mA | 705.411.1 | Additional protection against shock |
| Final circuits supplying socket-outlets rated above 32 A | 100 mA | 705.411.1 | Shock protection for large industrial sockets |
| All other circuits | 300 mA | 705.411.1 and 705.422.7 | Fault protection and protection against fire |
| Circuits essential to livestock life support (ventilation, feeding, etc.) | Designed case by case | 705.422.7 and 705.560.6 | Avoid unwanted loss of supply that would harm animals |
The 300 mA requirement is about fire, not shock. Straw, dust, dry feed and timber make a farm building one of the most combustible environments you will wire, and a low-level earth fault that would sit unnoticed for years in a house can smoulder in a barn. IET Guidance Note 7 makes the point that the RCD should be an S-type or time-delayed device where discrimination with downstream 30 mA devices is needed, so a fault in a socket circuit trips the local device and not the whole building.
Life support is the one deliberate exception. Regulation 705.422.7 recognises that in intensive livestock rearing, losing ventilation or feeding can kill animals in hours, so where the automatic disconnection of a circuit would cause that harm, the designer can use a different approach, such as an RCD that alarms rather than trips, or a separate supply arrangement. Regulation 705.560.6 goes further and calls for a safety service or standby supply where life support depends on electricity, with monitoring that alerts someone when the supply fails. If you find a broiler shed with the fans on a plain 300 mA RCD and nothing to warn the farmer, that is worth a conversation and a note on the report.
Why is supplementary bonding non-negotiable in livestock areas?
People stand in shoes on a dry floor and tolerate a touch voltage of 50 V for a fraction of a second. A cow stands on four wet hooves on concrete, with a low body resistance and a long path from a drinking bowl to the ground. Livestock can react to potential differences of only a few volts, and a herd that refuses to drink or gives less milk is a classic symptom of stray voltage across a parlour. That is why Regulation 705.415.2.1 requires supplementary equipotential bonding in locations intended for livestock, connecting all exposed-conductive-parts and extraneous-conductive-parts that animals can touch.
The same regulation says that where a metal grid is laid in the floor, or the floor contains reinforcement, it must be connected to the supplementary bonding. In practice that means bonding tails brought out to the reinforcement mesh before the concrete is poured, or a purpose-laid steel grid in the standing area, tied to the cubicle rails, feed barriers, water pipes, the parlour stalls and the CPCs of the circuits feeding that area. On new builds this is a coordination job with the builder that has to happen before the slab goes down. On existing buildings it is often missing entirely, and you cannot retrofit it to a slab, which is why an EICR on an old parlour so often ends up with a C2 for absent bonding.
A related point is the earthing arrangement itself. Regulation 705.411.4 states that in a TN system the PEN conductor must not be used downstream of the origin, so there is no TN-C within the installation. A TN-C-S supply is not prohibited by Section 705, but an open PEN on a PME supply raises every bonded part to a potential that animals will feel long before people do. Many designers therefore keep the PME earth in the farmhouse and take livestock buildings TT with their own electrodes, which brings the electrode testing described at Earth Electrode Testing for TT Systems: Methods and Limits and the arrangement comparison at Earthing Arrangements Explained: TN-S, TN-C-S and TT into play. Check what the DNO has actually provided rather than assuming.
What do the external influences do to equipment and cables?
Regulation 705.512.2 requires equipment in normal use to have a degree of protection of at least IP44, and where the external influences are more severe the selection must match them. The influences to think about on a typical farm are water (AD4 splashing and AD5 jets in wash-down areas), corrosive substances (AF4, ammonia from livestock waste and fertiliser dust), dust (AE), mechanical impact from animals and machinery (AG), and rodents. Sheds, dairies and parlours are washed with pressure hoses, so IP65 or IP66 gear with stainless or polymer fittings is the norm in those areas, and galvanised steel corrodes fast where ammonia is present.
Regulation 705.513.2 says switchgear and controlgear must be placed where livestock cannot reach it, and 705.522.16 requires wiring systems in areas accessible to animals to be inaccessible to them or protected against mechanical damage. A horse will chew a surface cable, a cow will lean on a trunking run until it splits, and rats treat PVC as a snack, which is why Regulation 705.522.10 asks for cables to be protected against rodents where they are present. Steel wire armoured cable, galvanised or polymer conduit, and cable runs kept above animal height are the practical answers. Table 4A2 of Appendix 4 and IET Guidance Note 1 give the selection detail.
Socket-outlets follow Regulation 705.553.1: industrial types to BS EN 60309-2 in the main, with BS 1363 outlets only where the rating and location make them suitable and they carry the IP rating the environment needs. The Electrical Safety First Best Practice Guides are worth a read for how these choices translate into codes on an EICR.
What are the fire rules for heaters and lamps?
Regulation 705.422.6 is short and specific: heating appliances used for the breeding and rearing of livestock must comply with their product standards and be fixed, with a clearance of at least 0.5 m from the animals and from combustible material, unless the manufacturer instructs a greater distance. In practice this is about the infra-red heat lamps used for piglets, lambs and chicks. They are often hung on a length of flex from a nail, over straw, with the lamp swinging within reach of the animal below. That arrangement fails 705.422.6 on every count.
Regulation 705.422.7, mentioned above, is the fire half of the RCD rule: for protection against fire, an RCD with a rated residual operating current not exceeding 300 mA must disconnect all live conductors, and where the circuit supplies life-support equipment the designer has to weigh the fire risk against the loss-of-supply risk. Regulation 422.3 on locations with combustible material and 422.4 on combustible constructional materials also apply to timber-framed barns and stores with hay or straw, which affects luminaire selection, the use of enclosed fittings, and keeping cables clear of stored material.
How do you test a Section 705 installation?
The tests are the same tests you run anywhere, but the priorities change. IET Guidance Note 3 is the reference, and the points below are where farms differ from domestic work.
Start with the earthing arrangement and bonding. On a TT installation measure the electrode resistance with the earth fault loop tester or a three-terminal electrode tester and check it against the 300 mA device: 50 V divided by 0.3 A gives 167 Ω, and GN3 recommends keeping electrodes at 200 Ω or below for stability, so you will usually want considerably less than 100 Ω across dry and wet seasons. Then prove the supplementary bonding with a low-resistance ohmmeter, working from the main earthing terminal or the local bonding bar out to each cubicle rail, water trough, feed barrier and the floor grid connection. Anything over a fraction of an ohm on a short bonding conductor points to a corroded clamp, and corroded clamps are the norm in a parlour.
Insulation resistance is the second headache. Damp, dust and ammonia bring readings down, and old rubber or damaged PVC cables in a shed can read below 1 MΩ. Test at 500 V on circuits with no electronics and drop to 250 V where variable-speed fan drives, milking controls or LED drivers cannot be disconnected. Where readings are low, the troubleshooting sequence at Low Insulation Resistance: Finding the Fault on Site applies. Then test every RCD at its rated current and at five times for the 30 mA devices, and confirm the 300 mA device trips within 300 ms at rated current, as covered at RCD Testing Explained: Types, Test Currents and Trip Times. Long runs across a yard put earth fault loop impedance under pressure, so compare Zs against the corrected maximum for the device, not the raw table figure.
Finally, check the paperwork. Regulation 705.514.9.3 requires a plan showing the location of equipment, the routing of concealed cables, a single-line diagram and the bonding arrangement. Most farms do not have one. It is not a code on the report, but it belongs in the observations and in your recommendations.
How do you code Section 705 defects on an EICR?
The table gives typical codes using the Electrical Safety First Best Practice Guide 4 approach. Use your own judgement on the day, and remember that the presence of livestock and a combustible environment shifts many findings from C3 to C2.
| Finding | Typical code | Reason |
|---|---|---|
| Socket circuit up to 32 A with no 30 mA RCD | C2 | Wet, conductive location; shock risk to people and animals |
| Non-socket circuit with no RCD at all (no 300 mA fire protection) | C2 | Fire risk in a combustible environment |
| No supplementary bonding to cubicle rails, troughs or floor grid in a livestock area | C2 | Livestock touch-voltage risk |
| Bare conductors where rodents have stripped a cable | C1 | Live parts accessible |
| Enclosure at IP20 in a wash-down area, water ingress present | C2 | Water on live parts likely |
| Radiant heat lamp on flex over straw, not fixed, under 0.5 m | C2 | Fire risk under 705.422.6 |
| Switchgear within reach of livestock | C2 or C3 | Depends on enclosure damage and access |
| No installation plan or single-line diagram | Note or recommendation | Not a danger; documentation gap under 705.514.9.3 |
| Consumer unit in a dusty grain store with no fire enclosure | C3 | Improvement recommended under 422 |
If you want the general framework for these decisions, the observation codes guide at EICR observation codes explained: C1, C2, C3 and FI and the ten most common fails at EICR Fails: The Ten Most Common C1 and C2 Observations cover the reasoning in more depth.
Sources
BS 7671:2018+A4:2026 Requirements for Electrical Installations, Section 705, Chapters 41 and 42 and Section 544; IET Guidance Note 3 Inspection and Testing; IET Guidance Note 7 Special Locations; Electrical Safety First Best Practice Guide 4; HSE agriculture guidance on electrical safety published via GOV.UK; NICEIC technical guidance on agricultural installations.
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