Free notes
Cable calculation, step 3: the design current, IbWhy might 230 volts be the wrong number?
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.
Ib = design current: how many amps the circuit will draw. It depends only on the load. From the power triangle, cover I and you're left with P over V.
Working
Ib = P ÷ V = 9600 ÷ 230 = 41.7 A (full load, every hob, oven and grill on full)
Use 230 V unless you know otherwise. One case where you do know otherwise:
One customer replaced an old garden shed with a summer house and a hot tub. There was "already a supply there": a 50–60 m run of about 4–6 mm² cable, fine for a light and a socket. The hot tub wouldn't work because of the voltage drop on that long run. Nobody had checked the existing installation first (Reg 132.16 again).
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