Electrical Engineer key topics and quick reference

Updated 17 September 2026 · 2 min read

Engineering judgement rests on facts that must be instant: the relationships between voltage, current, power and power factor, what an enclosure rating protects against, and what a conductor colour means. The reference tables on this page hold those facts. The notes explain how they combine in the decisions an engineer actually makes.

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	56%	6,523	Electrical
Electronics and automation	22%	504	Electrical
Maintenance practice	22%	1,784	Electrical

Formulas as a connected set

Learn the formulas as a web rather than a list. Power connects to current through voltage and power factor; current drives voltage drop through resistance and length; reactance links inductance and capacitance to frequency; the transformer ratio ties primary and secondary together. When a question gives you one quantity and asks for another, the path through that web is usually short.

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.

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

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.

Ratings that decide equipment choice

An IP rating states what an enclosure keeps out, and choosing it is a design decision tied to the environment: dust in a workshop, water in a plant room, weather outdoors. Under-specifying causes failures that look electrical but are environmental. Questions often describe a location and expect the rating to follow from it.

Colours, labels and the record

Conductor colours, labelling and up-to-date drawings are what allow the next person to work safely on your installation. Treat documentation as part of the design rather than paperwork after it, and expect test questions about identification and records.

Be able to state in one sentence

The relationship between kW, kVA and power factor.
Why a longer cable may need a larger conductor than its current rating suggests.
What discrimination between protective devices achieves.
What the two digits of an IP rating mean.
Why a transformer impedance affects the fault level downstream.

Common questions

Which relationships should I know without thinking?

Ohm's law, the power formulas, the three-phase power relationship and voltage drop. Almost every design calculation starts from one of them.

How detailed should my knowledge of standards be?

Know what each standard governs and the principles it enforces. Clause-level detail is looked up in practice, and tests reflect that.