SPARKYSTUDY NOTES
SPARKY STUDY NOTES sparkystudynotes.co.uk/learn/finding-a-fault-and-where-you-restart

Free notes

Finding a fault — and where you restartAfter a fix, where do you restart your tests?

Free from the notes: Sparky’s video on it, the section word for word as members see it, and a PDF to keep.

From Sparky’s full video lesson. Members get the whole lesson on every notes page.

The notes

Exactly as they are on the site.

Download these notesPDF · free to keep

Take that ring with the high neutral reading. Working the fault out is a better lesson than any diagram.

TestResult
Continuity, line and CPCGood — r1 0.01 Ω and r2 0.02 Ω, as expected
Insulation resistance, live conductors to earth (line and neutral joined, to CPC, global)> 2000 MΩ — good
Continuity, neutral end to end0.52 Ω against 0.01 Ω on the line — outside the 0.05 Ω tolerance
Insulation resistance, line to neutral (global)Fail
→Line and CPC continuity are good, and nothing is breaking down to earth. The two results that are wrong — neutral continuity and line-to-neutral insulation — both involve the neutral. So the neutral conductor is where you look first — and you've narrowed it down without opening anything up. That's fault finding.

What it's likely to be: a conductor slipped out of a terminal and touching something it shouldn't, a high-resistance joint, or damaged insulation with bare copper in contact somewhere.

The question that catches people

✋The fault gets rectified — a re-termination, or a new length of cable. Where do you restart the tests? Not from where it failed. You go back to the beginning of the sequence and start again at continuity.
Reg 643.1: when a test shows a failure, that test and those preceding, the results of which may have been influenced by the fault, are repeated after the fault has been put right. A new length of cable or a re-termination disturbs continuity, so here that is the whole sequence from continuity on.
Why. Whatever you did to fix it, you disturbed the installation. The continuity result you had before was taken on a circuit that no longer exists in that form. Re-terminate, retest continuity, then insulation resistance, then carry on through the sequence.
≡And if you're the tester rather than the installer, the installer goes back and fixes it. Then the whole sequence runs again.

GN3 · 2.6 · Figure 2.12 · p.57 · the sequence of tests ★ OSG · Section 10

Free section from Sparky Study Notes. The full Level 3 notes, 1,463 practice questions and the video lessons: sparkystudynotes.co.uk

Test yourself on it

The tests are in the members’ area. Get one wrong and it shows you why, and where to revise.

Get access

Get new notes and exam tips from Sparky

About one email a fortnight. Unsubscribe any time. Privacy notice

That was one section. There are 583.

Sparky Study Notes is the whole Level 3 syllabus written up like this: the explanation, the worked example, and where it is in your book. With a video lesson for every part and a practice paper for every exam.

  • 583sections of written notes
  • 35video lessons
  • 1,463practice questions
  • 146diagrams, redrawn
  • 18th Edition
  • Building Regs
  • PAT
  • Fundamental Inspection & Testing
  • Initial Verification
  • Periodic Inspection & Testing
Get access — £100 12 months. One payment. See what’s inside