Free notes
Global insulation resistance, RCBOs and sensitive equipmentWhy no global test with RCBOs in?
Free from the notes: Sparky’s video on it, the section word for word as members see it, and a PDF to keep.
The notes
Exactly as they are on the site.
Global insulation resistance and RCBOs
Figure 2.21 shows a global insulation resistance test with the RCBOs on, all conductors connected, and the lead clamped on the earth bar. Read a little further into the same section and the text tells you to disconnect them.
Worth stating twice: on RCBO circuits do individual insulation resistance tests, not a global one. You will get problems otherwise.
Why sensitive equipment comes out
Guidance Note 3 · pp.71–72 spells out the reason, and it is worth highlighting because it tells you how to interpret everything else:
Relays, contactors, electronic components, RCDs and RCBOs all behave this way. If a device is going to present a low resistance to your test, it has no business being connected while you take the reading.
| If you can | If you cannot |
|---|---|
| Disconnect it, or drop the front and bypass with connector blocks | Drop the test voltage to 250 V |
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 new notes and exam tips from Sparky
About one email a fortnight. Unsubscribe any time. Privacy noticeThat 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