Engineering Guides and Decision Tools

All 42 guides in this section

• Generator kVA and kW Sizing Guide — How to size a generator in kVA and kW: connected and running load, power factor, motor starting, derating, growth and the checks that stop undersizing and oversizing.
• Building an Electrical Load List: kW, kVA and Power Factor — How to build a load list with kW, kVA, power factor, duty and diversity: the columns that matter, where the numbers come from, and how the list feeds generator, UPS and cable sizing.
• Maximum Demand and Diversity: From Connected Load to Design Load — How to move from connected load to maximum demand using demand and diversity factors, with a worked example, typical pitfalls and guidance on measured data versus assumptions.
• Generator Capacity Requirement: From Load to Preliminary Size — A step-by-step method for estimating the generator capacity a site needs: running load, power factor, starting, derating, redundancy and growth, with a worked example and limits of the estimate.
• Generator Loading and Spare Capacity: How Hard Should a Set Run? — How to assess generator loading and spare capacity: target loading, light-load risks, headroom for steps and growth, and how to read a load profile against a generator’s rating.
• Generator Derating: Altitude, Temperature and Installation Effects — How altitude, ambient temperature, humidity, enclosure and ventilation reduce generator output, how to apply derating factors, and why manufacturer data governs the final number.
• Motor-Starting Generator Capacity Guide — How to check whether a generator can start a motor: starting kVA, voltage and frequency dip, load already running, and a worked screening example with its limits.
• Motor Starting Method and Generator Impact Selection Guide — How to choose a motor starting method to suit a generator: comparing DOL, star-delta, auto-transformer, soft starter and drive by current, torque, voltage dip and cost.
• Generator Load-Step and Transient Screening Guide — How to screen a generator for load steps: step size, voltage and frequency dip, recovery time, load staging and the point at which a detailed transient study is needed.
• Multi-Generator Capacity and Number of Generators — How to decide how many generators a site needs and in what sizes: load profile, redundancy, step handling, part-load efficiency, maintenance and growth, with a worked comparison of options.
• N, N+1, N+2 and 2N Capacity Guide — How to calculate installed capacity for N, N+1, N+2 and 2N power architectures, with unit-count tables, a worked example and the pitfalls of counting redundancy by number of units.
• Multi-Generator Operating Combination and Dispatch Selection — How to choose which generators to run as load changes: start and stop thresholds, running-hour balancing, redundancy margin, minimum loading and the dispatch rules for a parallel plant.
• Generator kW Load-Sharing Guide — How parallel generators share real power: droop and isochronous modes, load-sharing lines, governor settings, typical sharing errors and what to check when units do not share evenly.
• Generator kVAr and Power-Factor Sharing Guide — How parallel generators share reactive power: AVR droop, cross-current compensation, power-factor control, causes of circulating current and what to check when units carry unequal kVAr.
• Generator Synchronising Readiness Checklist — A checklist and decision guide for readiness to synchronise generators: the four conditions, phase sequence, protection, controls and tests to complete before closing a breaker onto a live bus.
• Diesel Generator Fuel Consumption Estimation Guide — How to estimate diesel generator fuel use from load: specific consumption, load percentage, typical litres per hour, cost per kWh, and why site data beats catalogue figures.
• Generator Fuel Tank and Runtime Guide — How to size a generator fuel tank for a target runtime: consumption, usable volume, reserve, day tank versus bulk storage, resupply planning and safety and regulatory points to check.
• Generator Rental Capacity and Runtime Planning Guide — How to plan a rental generator: sizing from the real load, runtime and fuel, connection method, cabling, protection and what to prepare so temporary power arrives and works first time.
• Cable Sizing and Voltage-Drop Screening Guide — How to screen cable size for current rating, voltage drop and short-circuit withstand, with a worked example, correction factors and the point at which a full design is needed.
• Transformer Capacity and Loading Guide — How to size and check a transformer: kVA rating, loading, load factor, overload capability, impedance, losses and the checks for generator and double-ended arrangements.
• Transformer Energisation and Inrush Screening Guide — How transformer inrush current arises when energised from a generator or grid, how to screen it, what it does to generators and protection, and ways to reduce it.
• Short-Circuit Study Requirement Screening Guide — How to decide whether a short-circuit study is needed and what it must cover: triggers such as new sources, ratings, paralleling, protection changes and the data to collect first.
• Protection and Coordination Study Requirement Selection Guide — How to decide which protection studies a site needs: coordination, selectivity, arc-flash, generator and transformer protection, with triggers, inputs and expected outputs.
• Power-Factor Correction and kVAr Requirement Guide — How to calculate the capacitor kVAr needed to improve power factor, with a worked example, generator and harmonic cautions, and when APFC panels or detuned reactors are needed.
• Harmonic Risk and Harmonic-Study Screening Guide — How to screen a site for harmonic risk: sources, the ratio of non-linear load to supply, generator sensitivity, symptoms, and when a harmonic study or filter is warranted.
• Power-Quality Problem to Required Study Selection Guide — Match a power-quality symptom, such as sags, flicker, harmonics, unbalance or transients, to the measurement or engineering study that finds the cause and the likely solutions.
• UPS Capacity and Load Guide — How to size a UPS: load in kW and kVA, power factor, crest factor, redundancy, growth, efficiency and the generator and battery implications that come with the chosen rating.
• UPS Battery Autonomy and Runtime Guide — A practical method for estimating UPS battery runtime and the battery size for a target autonomy, with worked numbers, correction factors, checks and how to confirm runtime on site.
• BESS Power (MW/kW) Requirement Guide — How to estimate the power rating a battery energy storage system needs for peak shaving, generator support, bridging or islanding, including motor starts, fault current and inverter limits.
• BESS Energy (MWh/kWh) and Runtime Guide — How to size BESS energy capacity for a target runtime: usable energy, depth of discharge, efficiency, degradation, reserve state of charge and a worked example of nominal versus usable kWh.
• DG + BESS Hybrid Capacity and Runtime Screening Guide — How to screen a diesel generator and battery hybrid: how to split load between engine and battery, expected fuel and runtime effects, sizing logic and the limits of a screening estimate.
• Critical-Load Classification and Priority Guide — A practical method to classify loads by consequence and tolerable outage, assign priority tiers, and use the result for generator, UPS, load-shedding and restart planning.
• Load-Shedding Requirement and Priority Planning Guide — How to decide whether load shedding is needed and plan it: capacity shortfall cases, shed tiers, triggers, staged shedding and restoration, with a worked shortfall example.
• Critical-Power Redundancy Architecture Selection Guide — A decision guide to choose between N, N+1, N+2, 2N and distributed redundancy from outage cost, failure to survive, maintainability and budget, with a scoring table and examples.
• ATS, STS and UPS Architecture Selection Guide — How to choose between ATS, STS, UPS and combinations for a load: transfer time needs, source types, load sensitivity, cost and maintenance, with a selection table and examples.
• Utility + DG + UPS + BESS Architecture Selection Guide — How to choose how utility, generator, UPS and BESS combine for a site: roles, topologies, selection by outage tolerance and duration, and the integration checks that decide success.
• Black-Start Readiness and Dependency Assessment Guide — A checklist to assess whether a site can restart from total blackout: black-start source, auxiliaries, control power, fuel, breaker closing and the dependencies that most often block restart.
• Islanding and Microgrid Readiness Assessment Guide — A structured way to judge whether a site can operate as an island or microgrid: sources, load balance, control, protection, grid interface, reserve and the gaps to close before attempting it.
• Generator Retrofit and Modernisation Decision Matrix — A decision matrix for upgrading an existing generator: controls, AVR, governor, ATS, emissions, fuel system and engine overhaul, with drivers, benefits, risks and when each upgrade pays back.
• Electrical Problem to Required Engineering Study Selection Guide — Match an electrical problem, such as tripping, overheating, voltage dips, faults, capacity limits or expansion plans, to the engineering study that finds the cause and the data you need.
• Critical-Power Requirement to Complete Solution Architecture Guide — Start from your requirement, outage tolerance, duration, load, site and compliance, and find the complete solution architecture of sources, protection, controls, testing and services.
• RECD, Dual Fuel or DG Replacement Decision Guide — How to compare retrofitting emission control (RECD), dual-fuel conversion and replacing a diesel generator: compliance, cost, performance, availability, risk and the data needed to decide.

Questions engineers ask

Can I size a generator from the total connected load?

Not reliably. Adding nameplates overstates the running load, while ignoring the largest motor start understates the generator needed. Build a load list, apply diversity, then check the largest step load.

How accurate are these guides?

They give screening-level answers based on stated typical values. Final sizing should use the actual equipment data and site conditions.

Engineering content reviewed by D. Srinivas Reddy, Managing Partner and Service Engineer, Reddy Generators. Last updated 8 November 2026. For advice on your own site, send us your requirement or call 98852 01608.