Electrician key topics and quick reference
Electricians rely on facts that must be recalled instantly and correctly, often while standing in front of a distribution board. The reference tables on this page cover the essentials: core formulas, conductor colours and IP ratings. The notes below explain how to memorise them effectively and how they connect in everyday installation and maintenance work.
How this guide was made
Written for this site with AI assistance, then checked automatically before publishing. The topic table, sample questions, worked examples and study plan are generated from this site’s question bank: each worked example is recalculated by separate code, and each sample answer says where it came from.
The guide deliberately states no salaries, grades, pass marks or exam dates. Those change, and they could not be checked here, so take them from the advert itself.
This site is independent and is not affiliated with MIFOTRA or any employer.
Where to spend your study time
The suggested emphasis reflects what this position works with day to day. It is a study guide, not a published exam blueprint.
| Area | Suggested emphasis | Questions in the bank | Practise |
|---|---|---|---|
| Electrical principles and installation | 71% | 6,523 | Electrical |
| Maintenance practice | 29% | 1,784 | Electrical |
Learning formulas so they stay
Do not just read the formula table. Derive the variations yourself: from P = V × I, work out I = P ÷ V and V = P ÷ I, then use each in a quick example. A formula you have used in several real calculations is much harder to forget under exam pressure than one you have only read.
Quick reference
Electrical formulas
| Quantity | Formula | Notes |
|---|---|---|
| Ohm’s law | V = I × R | Rearranges to I = V ÷ R and R = V ÷ I |
| Power | P = V × I = I² × R = V² ÷ R | Watts |
| Series resistance | R = R1 + R2 + … | Same current through each |
| Parallel resistance | 1/R = 1/R1 + 1/R2 + … | Same voltage across each |
| Energy | E (kWh) = P (kW) × t (h) | What a meter records |
| Three-phase power | P = √3 × VL × IL × cos φ | Balanced load, line values |
| Sine wave | VRMS = Vpeak ÷ √2 | 230 V RMS peaks at about 325 V |
| Capacitive reactance | Xc = 1 ÷ (2πfC) | Falls as frequency rises |
| Inductive reactance | XL = 2πfL | Rises with frequency |
| Transformer | Vp ÷ Vs = Np ÷ Ns | Ideal transformer |
| Single-phase voltage drop | Vd = 2 × L × I × ρ ÷ A | ρ of copper ≈ 0.0172 Ω·mm²/m |
Rwanda’s low-voltage supply is 230 V single-phase and 400 V three-phase at 50 Hz.
Conductor colours (IEC 60445)
| Conductor | Colour |
|---|---|
| Line (single-phase) | Brown |
| Neutral | Blue |
| Protective earth | Green-and-yellow |
| Three-phase L1 / L2 / L3 | Brown / black / grey |
Older installations may use earlier colour codes. Never identify a conductor by colour alone - test it.
IP ratings (IEC 60529)
| Rating | Solids | Water |
|---|---|---|
| IP20 | Fingers and objects over 12.5 mm | No protection |
| IP44 | Objects over 1 mm | Splashing from any direction |
| IP54 | Dust-protected | Splashing from any direction |
| IP65 | Dust-tight | Water jets |
| IP67 | Dust-tight | Temporary immersion |
Colours are a starting point, not proof
Conductor colours tell you what a conductor should be, but older installations and poor workmanship mean colours alone cannot be trusted. Know the standard colours for questions, and always test before relying on them in real work.
Matching IP ratings to locations
IP ratings describe how well an enclosure keeps out solids and water. Match them to the location: bathrooms and outdoor areas need higher ratings than dry indoor spaces. Questions often describe a location and ask which rating, or which fitting, is suitable.
Be able to explain in a sentence
- Why an RCD trips when current leaks to earth.
- How to find the current drawn by a 2,000 W appliance on 230 V.
- What the green-and-yellow conductor is for.
- Why a longer cable run increases voltage drop.
- What the two digits of an IP rating mean.
Common questions
Which formula should I learn first?
Ohm's law and the power formula, because most other electrical calculations are built on them.
Are IP ratings tested for electrician posts?
They can be, especially for installations in wet or dusty locations, where choosing the right equipment is part of doing the job safely.
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