Guides
Electrical guides
Explanations of low-voltage installation topics: voltage drop, cable sizing, derating and fault withstand, wire gauges, power factor, motor starters, transformers, earthing, RCDs and lighting levels, written for engineers, electricians and informed owners.
The guides below pair with the electrical calculators: the guide explains the physics and the standard, the tool does the arithmetic.
How voltage drop works
Why voltage falls along a cable, how to calculate it for DC, single-phase and three-phase circuits, what limits the common standards set, and what happens to equipment when the drop is too large.
Read guide →How to size a cable
The three checks a cable must pass, how the breaker rating and the cable's derated capacity are matched (Ib ≤ In ≤ Iz), what the IEC 60364-5-52 reference methods and correction factors mean, the voltage drop and fault-withstand checks, and the mistakes that undersize cables.
Read guide →The cable adiabatic check
Why a short circuit heats a conductor adiabatically and what I²t ÷ S² decides; where the k values of IEC 60364 come from; how the device's clearing time and let-through energy set the size; where the check bites; sizing protective conductors; and reading a breaker datasheet against (k × S)².
Read guide →AWG and mm² wire sizes
How the American Wire Gauge is defined and why three steps double the area; what IEC 60228 fixes about a mm² conductor; SWG and the 7/029 family on old Pakistani wiring; converting by area, not ampacity; resistance, mass and aluminium; and the mistakes where imported machines meet local cable.
Read guide →Single-phase and three-phase power
Why volts times amps is not the whole story in AC, where the √3 comes from, what kW, kVA and kVAr each measure, how to convert a motor's horsepower into the current it draws, and the mistakes that get cables and breakers wrong.
Read guide →Choosing a motor starter
Why an induction motor draws six to eight times its running current at switch-on, how direct-on-line, star-delta, soft starter and drive trade current against torque, cost and wear, the protection and coordination behind each, and what a hard start means for a generator.
Read guide →What power factor means
Power factor explained without hand-waving: the lag between voltage and current, real versus apparent power, what a low power factor costs in penalties, cable loss and capacity, how capacitor banks fix it, and where they make things worse.
Read guide →How to size a distribution transformer
Connected load, demand factor and a load study; kVA, power factor and growth; why a transformer is loaded to 80 % and what heat does to its insulation; what the percent impedance on the nameplate means and how it sets the fault current the LV switchgear must break; losses; one unit or two.
Read guide →How much light a room needs
Lux against lumens, the maintained illuminance EN 12464-1 asks for in offices, classrooms, workshops and warehouses, and the lumen method that turns that number into a count of luminaires: room index, utilisation factor, maintenance factor, spacing, glare, and what the installation costs to run.
Read guide →Earthing and electrode resistance
What an earth electrode is for, why soil resistivity decides its resistance, what the rod formula says about length and diameter, what more rods, longer rods and better soil buy, which value an installation actually needs, how TT earthing works in Pakistan, and how to measure it.
Read guide →RCDs explained
How an RCD compares the line and neutral currents and trips on the difference, what 30 mA means for a person, ratings and types (AC, A, F, B; RCCB, RCBO), what an RCD cannot do, the real causes of nuisance tripping, why TT installations in Pakistan depend on them, and how to choose and test one.
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