The appendices worth tabbingWhich appendix holds the time-current curves?

The contents list 17 appendices, but Appendix 7 and Appendix 17 are listed as deleted and Appendix 12 as not used, so 14 have content. Realistically five of them earn a tab. A quick tour of them:

Appendix 1 — British Standards

The list of BS and other standards referenced by the book. It is the one to read if you want to fall asleep. Know it exists; don't study it.

Appendix 2 — three pages, one useful table

Appendix 2 runs pp.434–436 — statutory regulations and associated memoranda. The only thing in it worth highlighting is the table at the very end, on p.436:

Nominal voltage to earth, U₀ = 230 V
Permitted tolerance = +10 % / −6 %

230 − 6 %  = 216 V
230 + 10 % = 253 V

In force since 1 January 1995

This answers a question raised earlier: can the supply coming into a property be more or less than 230 V? Yes — legitimately anywhere between 216 V and 253 V.

Appendix 3 — time/current characteristics

• Where you get your fault currents and disconnection times for overcurrent devices. You've now been in it repeatedly across these modules.
• Appendix 3 prints, with each set of curves, a table giving the current needed to operate the device within 0.1 s and within 5 s. That is where the t in the adiabatic equation comes from: the device's operating time, read from Appendix 3.
• The curved part of the characteristic is overload protection; the straight part is the high fault current giving you the 0.1 s or 0.4 s trip.
• Worked from it: a BS 88-2, 80 A fuse needs 750 A to operate in 0.4 s. Find the 0.4 s column and read the current: 750 A.

Appendix 4 — current-carrying capacity and circuit design

Enormous, and the one you'll live in during cable calculation work. Everything below sits in it.

Also in Appendix 4, and worth its own tab:

• Table 4Ab — voltage drop limits: 3 % for lighting, 5 % for everything else. At 230 V that's 6.9 V and 11.5 V. You won't have the On-Site Guide in the exam, so this is where you get them. Expect the question to want the volts, not the percentage.
• Table 4B1 — ambient temperature rating factors. Example: 70 °C thermoplastic at a 40 °C ambient gives C_A = 0.87.
• Installation reference methods — how cables may be installed and what's permitted, including reference method 100.
• The triple harmonics table, if a question ever asks about harmonic content in particular cable types.
• The I_z ≥ I_n formulas, several versions for different circumstances.

Appendix 5 — external influences

Any question about an external influence: Appendix 5 first, Chapter 52 second. Codes worth knowing:

• AG = impact. AG1 = low severity — normal household and similar equipment.
• AE = presence of foreign solid bodies — the IP-rating end of things.
• BA4 = instructed person, BA5 = skilled person.
• Temperature is an external influence too — which is why the sauna question is really an external-influence question.

Appendix 1 · British Standards Appendix 2 · p.436 · 230 V nominal · +10 % / −6 % · 216–253 V ★ Appendix 3 · time/current characteristics · BS 88-2 80 A at 0.4 s = 750 A Appendix 4 · C_A C_I C_G C_F · I_b I_n I_z I₂ ★ Table 4Ab · voltage drop 3 % / 5 % ★ Table 4B1 · ambient temperature · 40 °C = 0.87 Appendix 5 · external influences · AG1, AE, BA4, BA5 ★