Free mock exam
Cable Selection — Level 3 Systems Design Practice
Free topic-focused mock exam: 30 random questions from a pool of 65 on Cable Selection, drawn from the wider Level 3 Systems Design bank. 35-minute timer, 70% to pass, worked explanation on every question. Use this when you've taken the full mock once and want to drill the topics you got wrong.
- Questions
- 30
- Time limit
- 35 min
- Pass mark
- 70% · 21/30
- Question bank
- 65
Free, no sign-up. Retake as many times as you like — different questions each time.
Sample questions
01The three main factors that govern cable sizing are:
- Acost, appearance and the availability of the cable from the (local) wholesaler
- Bcurrent-carrying capacity, voltage drop and fault (thermal) protection
- Cambient temperature, humidity and the height (altitude) above sea level
- Dinsulation colour, run length and the manufacturer (brand) of the cable
Why: A cable must carry the design current, limit voltage drop and allow protective devices to operate correctly.
02In the relationship Ib ≤ In ≤ Iz:
- AIb is cable capacity, In is design current and Iz is the device rating
- Ball three symbols stand for prospective fault current, measured at the origin
- CIb is device rating, In is cable capacity and Iz is the design current
- DIb is design current, In is device rating and Iz is cable capacity
Why: Design current ≤ protective-device rating ≤ cable current-carrying capacity under the installed conditions.
03Rating factors reduce a cable's current-carrying capacity to account for:
- Athe colour, thickness and finish of the cable insulation
- Bthe rated current of the overcurrent protective device, and its breaking capacity
- Chigher ambient temperature, grouping and thermal insulation
- Dlonger cable runs, and the resulting increase in voltage drop
Why: Derating accounts for conditions that reduce heat dissipation: high temperature, grouped cables and thermal insulation.
Common questions
Is the Cable Selection mock exam free?
Yes — 100% free, no sign-up needed. Questions are pulled at random from a substantial bank, with a worked explanation on every question after you submit.
Can I retake the mock exam?
Yes. Every attempt picks a different random selection and reshuffles the options, so each retake gives you genuinely new questions. No limit on retakes.
Does this count towards the real qualification?
No — this is independent practice material. To gain the actual qualification you need to sit the official assessment through an approved provider.
