A complete guide to finding and diagnosing electrical faults — earth faults, open circuits, short circuits, and high resistance joints. Test sequence, tools, and safe isolation procedure.
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
Understanding the type of fault before picking up test equipment saves time and reduces the risk of making the fault worse. The four main fault types are:
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.
The fault-finding test sequence follows a logical order that moves from safe de-energised tests to energised tests, only progressing if previous tests are satisfactory.
See the EICR observation codes guide for how these test results translate into EICR codes and required remedial actions.
Earth faults are the most common cause of RCD tripping in domestic and commercial installations. The fault diagnosis approach depends on whether the RCD trips immediately on reset or only when a load is applied.
An open circuit fault means part or all of the circuit has no continuity — the conductor is broken, a terminal is disconnected, or a contact has failed. The circuit does not trip but simply does not work.
16 certificate types, 70+ calculators, RAMS, quoting, invoicing, AI agents, and 46+ training courses — from £6.99/mo.
Start free trial
High resistance faults are the most dangerous because they typically do not cause protective devices to operate — yet they generate sufficient heat to ignite nearby materials.
Having the right test equipment and knowing how to use it correctly is the foundation of effective fault finding.
Log test results, generate EICRs, and share observation reports with clients directly from your phone. No paper, no desktop required.
Try Elec-Mate freeFollow this systematic procedure to diagnose electrical faults safely and efficiently.
Before testing, establish what the fault symptoms are: which circuits have tripped or failed; whether the problem is intermittent or permanent; when it started; and whether any work was recently carried out. Note whether the MCB trips immediately on reset (short circuit or earth fault), trips after a delay (overload or high resistance), or fails to trip at all (open circuit or RCD fault).
Isolate the affected circuit at the consumer unit. Prove dead with an approved voltage indicator (GS38 compliant). Lock off the MCB or remove the fuse. Apply a warning label. Do not rely on a neon screwdriver as the sole means of proving dead.
For a ring main, measure end-to-end continuity of line, neutral, and CPC (earth) conductors. For a radial circuit, measure from consumer unit to end of circuit. High resistance on the CPC compared to the line conductor (more than 1.67 times for same CSA) indicates a CPC fault. Use a low-resistance ohmmeter or the continuity range of your MFT. Record results and compare against calculated R1+R2.
With all equipment disconnected from the circuit, apply 500V DC between line and earth, neutral and earth, and line and neutral. Record readings in MΩ. Readings must be at least 1MΩ (BS 7671 Table 64). A reading below 0.5MΩ indicates a serious defect. If a circuit shows low IR, systematically disconnect socket outlets and appliances to identify the faulty section.
Using the MFT RCD test function: apply a ramp test to confirm the RCD trips at or below IΔn (30mA for 30mA RCDs). Apply x1 IΔn test and confirm disconnection within 300ms. Apply x5 IΔn test and confirm disconnection within 40ms. For Type S or time-delayed RCDs, confirm disconnection within 500ms at x1 IΔn. Record all test results.
Re-energise the circuit and measure Zs at the furthest point. Compare against the maximum permitted Zs for the protective device (from BS 7671 tables). High Zs can indicate a broken CPC, a high-resistance joint, or a supply problem (high Ze). If Zs is too high, the circuit may not disconnect within the required time on a fault.
Verified 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
Generate EICRs and observation reports from your phone. Share results with clients instantly. No paper required.
“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