Guides

Engineering guides

Short, technical explanations written to answer one question properly: the physics, the numbers, the standard that applies, a diagram where one helps, and how to use the related tool.

Each guide is written by our engineers, states its publication and last-update dates, and cites the standards or sources it relies on. We publish a guide when we have something specific to explain, not on a schedule.

Electrical

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Energy

How to size solar arrays, orient the panels, choose a charge controller and an inverter type, work out the payback, charge a battery properly, size a UPS or a standby generator and what it costs to run, and find where the units on the bill go.

How to size a solar system

A step-by-step method for sizing a rooftop or off-grid solar system in Pakistan: measure the energy, find the peak sun hours for your site and worst month, apply honest losses, then choose panels, battery, inverter and cables that fit each other.

How to size a UPS

What a UPS is for and what an inverter is for; VA, watts and the power factor trap; the three topologies of IEC 62040-3; runtime, Peukert and the C-rate; measuring the real load; generators and UPSs; the worked example; and the installation details that decide battery life.

How to size a standby generator

Running load, motor starting, kW against kVA, prime and standby ratings, derating for heat and altitude, and the trap of an oversized diesel: how to arrive at a generator size that starts everything and still runs healthily.

What a generator costs to run

Litres per kWh, not litres per hour; the fuel line and why a lightly loaded diesel is expensive twice; reading the datasheet; the diesel unit against the grid and against solar; how sizing and cost interact; the service costs nobody writes down; and what cuts the bill without a new set.

How to orient solar panels

Why the best tilt is a little less than the latitude, why direction matters more than tilt on a real roof, what an east or west roof costs, when adjusting twice a year is worth it, and how dust and the tariff change the answer.

Grid-tied, hybrid or off-grid

How grid-tied, hybrid and off-grid solar systems work, what anti-islanding means during load-shedding, the "solar UPS" market and what to demand of a hybrid inverter, batteries for each case, sizing in a paragraph each, net-metering approvals and the meter, and what we honestly recommend.

Solar payback and net metering

The three numbers that decide a solar payback: specific yield and where to get it, the self-consumption share the quotation never states, and the export credit; how net metering works at the DISCO; what a quotation should show; financing; a worked 10 kWp example; and when solar does not pay.

Choosing a solar charge controller

What a charge controller does; PWM as a switch and MPPT as a converter; the voltage window set by the coldest morning and the hottest afternoon; the 1.25 current factor; how to read a controller datasheet; a worked two-string example; and the installation errors seen in Pakistan.

Where your electricity units go

A unit is a kilowatt-hour, and what an appliance costs depends less on its rating than on how much of the time it actually draws it. The arithmetic for the air conditioner, pump, geyser, fridge, fans and lights of a Pakistani home, the slab trap, standby loads and how to measure.

How long a battery takes to charge

Charge efficiency, the three stages of a charger, C-rate limits by chemistry, why the absorption stage cannot be hurried, what solar changes, and the load-shedding arithmetic that kills lead-acid batteries by never letting them fill.

Electronics

Short explanations of circuit-level decisions: LED resistors, voltage dividers and loading, RC filters, the 555 timer, keeping power parts cool, power budgeting for battery devices, PCB trace width, and what changes when a prototype has to ship.

Choosing an LED series resistor

Why an LED cannot be connected straight to a supply, how the series resistor sets the current, what forward voltage really is, how much headroom to leave, how to pick a standard value and a power rating, and when a resistor is the wrong tool.

Voltage dividers and loading

The ideal divider is a ratio; the real one is a source with an output impedance. Thévenin, the ten-times rule, how ADC inputs, transistor bases and meters load a divider, choosing the resistor values, tolerance, where a divider is the wrong part, and a 12 V battery monitor worked through.

RC filters in practice

What the time constant and the −3 dB cutoff of an RC filter mean, why 20 dB per decade is often not enough, and how the one-resistor-one-capacitor filter is used to debounce a switch, smooth a sensor, turn PWM into a voltage, and why the source and the load are part of it.

The 555 timer in practice

What is inside the 555 and why every circuit on it times a capacitor between ⅓ and ⅔ of the supply; the astable and monostable in detail; capacitors and resistors that hold the timing; bipolar against CMOS; the traps that cost an afternoon; and where a 555 still beats a microcontroller.

Keeping power semiconductors cool

Why the junction temperature decides a power device's life; the three thermal resistances in series from junction to air; where the watts come from; grease, pads and torque; heat sinks in still air, in an enclosure and with a fan; measuring; and when a heat sink is the wrong answer.

Power budgeting for battery devices

Why a battery-powered device lives or dies by its average current; the shape of a wake-measure-transmit burst; the sleep floor and the parts that quietly raise it; choosing a cell for the load; regulators at microamp loads; firmware that keeps a node asleep; and measuring it.

PCB trace width and current

A copper trace is a resistor with poor cooling: where its heat goes, the IPC-2221 curve, why an inner trace needs twice the width, the vias and terminals that limit first, voltage drop and Kelvin sense lines, copper weight and pours, and checking a finished board.

From dev board to product

The prototype works on the bench; a product has to answer different questions. What the dev board hid, power input, inputs and outputs that survive the field, the board and its supply chain, the enclosure, firmware for a product, EMC, safety and radio approval, documentation, and the stages between.

Automation

How current loops carry a measurement to a PLC, how milliamps become engineering units, how to tune a PID loop, wire a PT100, turn a level into litres, choose between a PLC, a microcontroller and an industrial PC, and make Modbus behave: the fundamentals behind our automation work.

How 4–20 mA current loops work

Why process signals are currents rather than voltages, why zero is 4 mA, what sits in a loop and how much voltage it needs, how a PLC scales milliamps into bar and raw counts, the NAMUR NE 43 fault bands, grounding and shields, and when a plain loop still beats a fieldbus.

How to size a pump motor

Flow, head and the duty point; hydraulic power and why head is not pressure; pump efficiency and the best efficiency point; margins, IEC ratings and the run-out case; motor efficiency, current and the cable; specific energy per cubic metre; and what a variable-speed drive changes.

PID tuning from a step test

What P, I and D each do; how to bump a loop in manual and read K, τ and θ off the trend; what the Ziegler–Nichols and SIMC rules are designed for; the ultimate-gain test and autotuners; the vendor forms and units that trip people; fine-tuning afterwards; and the loops these rules do not fit.

PT100 sensors and wiring

Why platinum and why 100 Ω; the Callendar–Van Dusen curve; what 2-, 3- and 4-wire connections do about lead resistance; immersion, thermowells and response time; self-heating; tolerance classes against installed accuracy; head-mounted transmitters; and fault-finding a PT100 loop with a multimeter.

Level measurement and tank volume

A transmitter reports a height and the plant wants litres: the geometry of vertical, horizontal and dished tanks; hydrostatic, ultrasonic, radar, float and capacitance transmitters and where each fails; PLC scaling by formula or strapping table; alarms, overfill protection and installation details.

PLC, microcontroller or industrial PC

What a PLC, a custom microcontroller board and an industrial PC each give you and cost you; the questions that decide (I/O, safety, timing, quantity, maintenance, lifetime, integration); the combinations that work; spares, technicians, heat and power in Pakistan; three typical examples.

Modbus RTU and TCP explained

One master, many slaves and four register tables; the off-by-one in addressing; 32-bit values and word order; the RTU frame, CRC and timing; RS-485 wiring, termination and bias; Modbus TCP and gateways; how many registers a second a bus carries; diagnostics; where Modbus is the wrong tool.