MCB, RCD, RCBO, AFDD, SPD, PFC, Ze, Zs, CPC, PME, TN-S, TN-C-S, TT — the electrical trade runs on acronyms. This A-Z reference explains every one you will encounter in UK installation, testing, and certification work.
Free for 7 days · No charge until day 8 · Cancel anytime · Used by 1,000+ UK electricians
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.
1,000+
UK electricians
“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”
Daniel Palmer — DP Electrical
Walk onto any job site and the conversation is a stream of letters: MCB, RCD, RCBO, CPC, PME, PFC, Zs, Ze, R1+R2, EICR, EIC, C1, C2, FI. For apprentices, it can feel like learning a new language. For experienced electricians, these acronyms are second nature — but even qualified sparks occasionally encounter one they need to look up.
This glossary covers every common electrical acronym used in UK installation work, testing, and certification. Each entry explains what the acronym stands for, what it means in practice, and why it matters. Use it as a reference whenever you encounter an unfamiliar term — whether you are studying for your 18th Edition exam, filling in an EICR, or explaining something to a customer.
Every key change in the 2026 amendment on one page. AFDDs, TN-C-S protection, new schedule columns, model forms. Pinned on your van dash.
Protects a circuit against overcurrent (overload and short circuit). Contains a thermal element (bimetallic strip) that trips on sustained overload and a magnetic element (solenoid) that trips instantly on short circuit. Available in Type B, C, and D — the type determines the instantaneous trip threshold. Type B trips at 3-5x rated current (domestic). Type C at 5-10x (commercial/motor circuits). Type D at 10-20x (heavy inductive loads).
Detects earth leakage by comparing current on the line and neutral conductors. If the difference exceeds the rated sensitivity (typically 30mA for personal protection), the RCD trips. Protects against electric shock from indirect contact and reduces fire risk from earth faults. Does not protect against overcurrent — that is the MCB's job. See our full guide to RCDs.
One of the most significant changes introduced by BS 7671:2018+A4:2026 is Regulation 411.3.4: all AC final circuits supplying luminaires (light fittings) in domestic premises must now be provided with additional protection by an RCD with a rated residual operating current not exceeding 30mA. The requirement uses "shall" — it is mandatory, not advisory. Lighting circuits were previously exempt from mandatory 30mA RCD protection in many existing installations, making this one of the most impactful new obligations for new domestic wiring and rewires post-A4.
Combines MCB and RCD protection in one device. Provides overcurrent protection and earth leakage protection for an individual circuit. The key advantage is selectivity — a fault on one circuit trips only that RCBO, not an entire bank of circuits. Increasingly used in new consumer units. See RCBO vs RCD+MCB comparison.
Detects dangerous electrical arcing — from damaged insulation, crushed cables, or loose connections — and disconnects the circuit before a fire starts. Analyses the waveform of the current for arc signatures. Recommended by BS 7671:2018+A4:2026 Regulation 421.1.7 for AC final circuits of a fixed installation to mitigate the risk of fire from arc fault currents. The wording is recommendatory, not mandatory — the regulation uses 'recommending' rather than 'shall'.
Protects the installation and connected equipment against transient overvoltages (voltage spikes) caused by lightning or switching operations. Required by BS 7671 Regulation 443 in most new installations and rewires where the consequence of an overvoltage could be serious (injury, loss of life, disruption to public services). Fitted at the origin of the installation, between line and earth.
Elec-Mate's voice entry feature lets you speak your test results — 'Ring 1, R1+R2 0.32, Zs 0.89…
Try it free for 7 days
The earthing system determines how the installation is connected to the general mass of earth. It affects bonding requirements, protective device selection, and the maximum Zs values that can be achieved. See our full guide to earthing.
The supply has separate neutral and earth conductors all the way back to the transformer. The earth conductor is typically the metal sheath or armouring of the supply cable. Common in older properties with lead-sheathed supply cables. Typical Ze: 0.35-0.8Ω. Generally the most reliable earthing arrangement.
The supply neutral also serves as the earth (PEN conductor) in the supply cable. At the consumer's origin, the PEN is split into separate N and E. This is Protective Multiple Earthing (PME) — the most common arrangement for newer UK domestic properties. Typical Ze: 0.2-0.35Ω. The risk is an open PEN fault, which is why PME supplies have strict bonding requirements.
The installation has its own earth electrode (typically a driven rod) with no metallic earth return through the supply. Common in rural properties and overhead supply areas. Ze can be very high (often 20Ω or more), so fault loop impedance values are much higher than TN systems. RCD protection is essential on TT systems because the high Zs means MCBs alone cannot disconnect fast enough under earth fault conditions.
16 certificate types, 70+ calculators, RAMS, quoting, invoicing, AI agents, and 46+ training courses — from £6.99/mo.
Start free trialPoint your phone camera at the distribution board and Elec-Mate reads the MCB ratings, circuit details, and board layout from the photo.
Try it free for 7 daysVerified reviews from the UK App Store.
Elec-Mate is my go to app for business and electrical work. It's feature rich without feeling cluttered. A true all in one app for quotes, certs, calculations, RAMS, EICRs, and more. I use it every day without fail, and it makes my workflow much smoother since I'm not jumping between apps anymore. The price-to-feature ratio is excellent. Any issues I've had, the developer responds within the hour and usually fixes them the same day. 100% recommend.
I've used the app and the web based version for a while now and it's well worth the investment. If you're an apprentice or experienced Spark give it a go, you won't be disappointed.
I've been using Elec-Mate for a while now, and honestly, it's one of the best apps I've ever downloaded. Every aspect of it feels thoughtfully designed, from the clean and intuitive interface to the powerful features that make everything so easy to manage. It's clear that a lot of care and attention went into building this app, and it shows in every detail.
Real feedback from real sparks
“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”
Daniel Palmer
Sole Trader · DP Electrical
“I've won two contracts this month because I could turn quotes around same-day with the AI cost engineer.”
Nathan Perry
Electrician · NP Electrical Services
“The study centre got me through my AM2. Mock exams and flashcards are brilliant.”
Jake Pizey
3rd Year Apprentice · Apprentice
Elec-Mate's built-in AI assistant explains any electrical term or acronym instantly. Ask it during a certificate, a study session, or on site. 7-day free trial, cancel anytime.
“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”
Daniel Palmer, DP Electrical
From £6.99/mo after trial — less than a coffee a week
We use cookies to improve the app and measure what works. Cookie Policy