ON-SITE RAPID LOOKUP
Pocket Electrical Cheat Sheets
Field-ready reference tables and interactive lookup tools calibrated to BS 7671:2018+A3:2024, BS EN 60529, and UK statutory standards. Designed for high-speed verification on phones, tablets, and field test instruments.
BS EN 60529
1. Ingress Protection (IP Code) Reference Deck
An IP rating defines the level of sealing effectiveness of electrical enclosures against foreign bodies (tools, dirt, dust) and moisture.
⚙️ Interactive IP Code DecoderSelect both digits to decode test specs and on-site applications
IP55Outdoor Weatherproof
Solid Ingress:Ingress of dust is not entirely prevented, but does not enter in sufficient quantity to interfere with safe operation.
Water Ingress:Protected against low-pressure water jets from all directions (12.5 litres/min at 30 kPa from 3 metres).
Typical Site Use:Standard industrial switchgear enclosures, commercial EV chargers, and unwashed external lighting.
| Installation Environment / Equipment | Min IP Rating | Standard / Regulation | Operational Notes |
|---|---|---|---|
| Bathroom Zone 0 (Interior of bath/basin) | IPX7 | BS 7671 Reg 701.512.2 | Protected against submersion to 1m. SELV ≤ 12V AC only. |
| Bathroom Zone 1 & Zone 2 (General) | IPX4 | BS 7671 Reg 701.512.2 | Splash-proof from any direction. 30mA RCD mandatory. |
| Bathroom Zone 1 & Zone 2 (Cleaning jets used) | IPX5 | BS 7671 Reg 701.512.2 | Required where water jets are used for cleaning (e.g. communal showers). |
| Outdoor EV Charging Points | IP54 | BS 7671 Section 722 • BS EN 61851 | Dust protected and resistant to rain/splashing outdoors. |
| External Domestic Sockets (Weatherproof) | IP66 (closed) / IP56 (in use) | BS 1363-2 • BS 7671 Reg 512.2 | Maintains seal with standard 13A plug molded lead inserted. |
| Industrial Food & Beverage Washdown | IP66 / IP69K | BS EN 60529 / DIN 40050-9 | Resistant to high-pressure steam cleaning (80°C @ 100 bar). |
| Underground Joint Boxes / Cable Pits | IP68 | BS EN 60529 • BS 7671 Reg 522.5 | Continuous submersion under head of water. Resin or gel filled. |
| Top Surface of Consumer Units / Boards | IP4X / IPXXD | BS 7671 Reg 416.2.2 | No entry of 1.0mm wire. Mandatory for horizontal top surfaces. |
| Front / Side Surfaces of Consumer Units | IP2X / IPXXB | BS 7671 Reg 416.2.1 | No finger contact with hazardous live parts (80mm probe Ø12mm). |
BS 7671 Section 701
2. Bathroom & Shower Zones Spatial Reference
Locations containing a bath or shower present increased shock risk due to reduced skin resistance in wet contact. Section 701 prescribes rigorous zone boundaries and protective measures.
BS 7671:2018+A3:2024 §701.32Spatial Boundary Geometry
┌─────────────────────────────────────────────────────────────────────────────────────────┐ │ OUTSIDE ZONES │ │ (230V Socket-Outlets permitted ≥ 2.5m from Zone 1) │ ├─────────────────────────────────────────────────────────────────────────────────────────┤ │ │ │ │ 2.25m │ │ │ HEIGHT │ │ │ ┌──────────────────────┐ ┌──────────────┴──────────────┐ ┌────────────────────────────┐ │ │ │ ZONE 2 │ │ ZONE 1 │ │ ZONE 2 │ │ │ │ (0.60m perimeter │ │ (Over bath / shower basin │ │ (0.60m perimeter │ │ │ │ up to 2.25m height │ │ to 2.25m or shower head) │ │ up to 2.25m height │ │ │ │ Min IPX4 │ │ Min IPX4 / IPX5 │ │ Min IPX4 │ │ │ │ Shaver unit OK) │ │ 30mA RCD mandatory) │ │ Shaver unit OK) │ │ │ └──────────┬───────────┘ └──────────────┬──────────────┘ └─────────────┬──────────────┘ │ │ │ ┌──────────────┴──────────────┐ │ │ │ │ │ ZONE 0 │ │ │ │ │ │ (Interior of bath / basin) │ │ │ │ │ │ Min IPX7 • SELV ≤12V AC │ │ │ │ │ └─────────────────────────────┘ │ │ │ ───────────┴───────────────────────────────────────────────────────────┴─────────────── │ │ FINISHED FLOOR LEVEL (FFL) │ └─────────────────────────────────────────────────────────────────────────────────────────┘
| Zone Designation | Dimensional Boundary | Min IP | Permitted Equipment & Switchgear | RCD & SELV Rules |
|---|---|---|---|---|
| Zone 0 | Interior of bath tub or shower basin. For shower without basin: 0.10m height and 1.20m radius from fixed water outlet. | IPX7 | Only equipment specifically intended for use inside bath (submerged luminaires, whirlpool jets). Fixed equipment only. | SELV only with nominal voltage ≤ 12V AC RMS or ≤ 30V ripple-free DC. Safety source must reside outside Zones 0, 1, 2. |
| Zone 1 | Vertical plane bounding bath/shower tray up to 2.25m above finished floor level (or highest fixed shower head position if higher). | IPX4 (IPX5 for jets) | Fixed water heaters, electric showers, shower pumps, luminaires, extraction fans. No standard switches or 13A socket-outlets. | All LV circuits require 30mA RCD (Reg 701.411.3.3). SELV ≤ 25V AC / ≤ 60V DC permitted. |
| Zone 2 | Vertical plane extending 0.60m horizontally outside Zone 1 boundary, up to 2.25m above finished floor level. | IPX4 (IPX5 for jets) | Luminaires, ventilation fans, towel rails, water heaters. Shaver supply units to BS EN 61558-2-5 permitted. | All LV circuits require 30mA RCD. Standard 13A sockets prohibited. |
| Outside Zones | The remaining space within the room beyond Zone 2 and above 2.25m height. | IPX0 (normal) | Standard switches, accessories, fused connection units. 13A 230V socket-outlets permitted ONLY if ≥ 2.5m from Zone 1 boundary. | All low-voltage circuits within the location require 30mA RCD protection (BS 7671 Reg 701.411.3.3). |
⚡ Supplementary Equipotential Bonding Exemption (Reg 701.415.2)
Local supplementary equipotential bonding in bathrooms may be omitted ONLY IF ALL THREE of the following conditions are verified:
- 1. Main Bonding in place: All incoming metallic service pipes (water, gas) are effectively bonded to the main earthing terminal (MET) per Reg 411.3.1.2.
- 2. 30mA RCD on all circuits: Every final circuit (lighting, shower, power) entering or passing through the room is protected by a 30mA RCD with automatic disconnection verified.
- 3. Extraneous continuity: All extraneous conductive parts are effectively connected to the protective equipotential bonding system.
BS 7671 Part 2 • Table 54.8
3. Earthing Systems Quick-Comparison Matrix
Comprehensive comparison of UK supply earthing arrangements: TN-S, TN-C-S (PME), and TT systems, including maximum typical source impedances, main bonding rules, and broken neutral hazards.
TN-S
Terre-Neutre Séparé
Typical Max Supply Ze:0.35 Ω
Earth Path:Lead sheath / separate armour back to DNO substation star point.
Main Protective Bonding:Table 54.7 sizing (Typically 10mm² or 6mm² Cu).
Neutral and Protective Earth conductors are separated throughout the distribution and installation network. No circulating neutral currents through extraneous pipework.
TN-C-S / PME
Protective Multiple Earthing
Typical Max Supply Ze:0.80 Ω
Earth Path:Combined PEN conductor in supply; separated at service cutout.
Main Protective Bonding:Table 54.8: 10mm² Cu (≤ 35mm² neutral), 16mm² Cu (> 35 ≤ 50mm²).
Most common modern UK supply. Broken PEN Hazard: If supply PEN is severed, diverted neutral load currents elevate exposed metalwork to dangerous touch voltages.
TT
Terra-Terra (Independent Rod)
Typical Max Supply Ze:21 Ω (Nominal DNO) • Rod RA < 200 Ω
Earth Path:Local earth electrode (rod/plate/mesh) through mass of earth.
Main Protective Bonding:Table 54.7 / 54.8: Typically 6mm² or 10mm² Cu.
No earth path provided by supplier. RCD mandatory for fault protection (RA × IΔn ≤ 50V). Immune to DNO broken PEN conductor hazards.
Main Protective Bonding Sizing (BS 7671 Table 54.8 for PME)
| Copper Equivalent CSA of Supply Neutral | Min Copper Main Bonding Conductor CSA | Min Aluminium Main Bonding Conductor CSA | Application Context |
|---|---|---|---|
| S ≤ 35 mm² | 10 mm² | 25 mm² | Standard domestic & small commercial installations (100A supply). |
| 35 mm² < S ≤ 50 mm² | 16 mm² | 35 mm² | Commercial TP&N supplies (up to 200A). |
| S > 50 mm² | 25 mm² | 50 mm² | Heavy industrial supplies & transformer fed installations. |
🚫 Statutory & BS 7671 Restrictions on PME Earthing
PME (TN-C-S) earth terminals must NOT be exported or used for the following installations without dedicated mitigation:
- EV Outdoor Charge Points (Section 722): Prohibited unless using open-PEN detection device (Reg 722.411.4.1), independent earth rod with touch voltage < 70V, or isolated transformer.
- Petrol Filling Stations & DSEAR Hazardous Zones: Prohibited due to circulating stray currents causing ignition arcs.
- Agricultural & Horticultural Premises (Section 705): High animal sensitivity to low step/touch potentials (≤ 25V). TT conversion recommended.
- Caravan Parks & Marinas (Section 708 / 709): PME earth must not be connected to caravan or boat hulls. TT supplies required.
BS 7671 Table 41.1
4. Maximum Disconnection Times Reference Deck
Maximum operating times for protective devices under Automatic Disconnection of Supply (ADS) in accordance with BS 7671:2018+A3:2024 Chapter 41.
| Nominal Voltage (U0) | Final Circuits ≤ 32A (TN System) | Final Circuits ≤ 32A (TT System) | Circuits > 32A & Distribution | Standard Reference |
|---|---|---|---|---|
| 120V < U0 ≤ 230V AC (UK Standard 230V) | 0.4 seconds | 0.2 seconds | 5.0 s (TN) / 1.0 s (TT) | Table 41.1 • Reg 411.3.2.2 |
| 230V < U0 ≤ 400V AC (UK Standard 400V 3-Phase) | 0.2 seconds | 0.07 seconds | 5.0 s (TN) / 1.0 s (TT) | Table 41.1 • Reg 411.3.2.2 |
| U0 > 400V AC (High voltage low frequency) | 0.1 seconds | 0.04 seconds | 5.0 s (TN) / 1.0 s (TT) | Table 41.1 • Reg 411.3.2.2 |
| 120V < U0 ≤ 230V DC | 5.0 seconds | 0.4 seconds | 5.0 s (TN) / 1.0 s (TT) | Table 41.1 (DC Systems) |
| Reduced Low Voltage (110V CTE Construction) | 5.0 seconds (Fixed) / 0.4 s (Sockets) | N/A (Centre-tapped earth) | 5.0 seconds | BS 7671 Section 411.8 |
Reg 411.3.2.3
Distribution Circuits (TN Systems)
A maximum disconnection time of 5.0 seconds is permitted for distribution circuits and final circuits exceeding 32A where no socket-outlets are supplied.
Reg 411.3.2.4
Distribution Circuits (TT Systems)
A maximum disconnection time of 1.0 second is permitted for distribution circuits and final circuits exceeding 32A in TT systems.
Reg 411.3.3
Socket-Outlets ≤ 32A Mandatory RCD
Socket-outlets ≤ 32A in locations where they may be used by ordinary persons require 30mA RCD protection with 300ms maximum trip at 1× IΔn.