Engineering Blog
Guides, standards updates, and calculation tips for electrical engineers.
BS 7671 Amendment 4: What's Changing in the Orange Book (2026)
A practising field engineer's guide to BS 7671 Amendment 4. Covers PoE derating, buried duct data, transition timeline, and what it means for your cable sizing calculations.
Arc Flash Boundary Calculation: IEEE 1584-2018 Guide [Free]
Calculate arc flash incident energy per IEEE 1584-2018, select PPE per NFPA 70E. Worked example at 480V MCC, 35kA. Free calculator — no signup required.
AS/NZS 3008.1.1:2017 — Understanding the Cable Sizing Tables (Appendix A vs B)
A deep dive into AS/NZS 3008.1.1:2017 cable sizing tables — installation methods (Table 3), current ratings (Tables 13-14), derating factors (Tables 22, 25, 27, 28), and the critical difference between Appendix A and Appendix B approaches.
BS 7671:2018 Amendment 3 — What Changed for Industrial Installations
Amendment 3 to BS 7671:2018 introduced significant changes affecting industrial installations — updated fault protection, revised cable selection, new AFDD requirements, and modified protective conductor sizing. Here is what changed and what needs review.
How to Apply Diversity Factors in Maximum Demand Calculations (AS/NZS 3000)
Diversity factors are the difference between a 400A switchboard and a 1000A switchboard. Learn how to correctly apply AS/NZS 3000 Appendix C diversity to industrial, commercial, and residential loads.
Earthing System Design: TN-S vs TN-C-S vs TT — Which to Choose and How to Calculate
TN-S, TN-C-S, and TT earthing systems each have different fault current paths, protection requirements, and failure modes. Learn how to select the right system and calculate earth fault loop impedance.
Your First Cable Sizing Calculation: A Tutorial for Junior Engineers
Step-by-step cable sizing tutorial for junior engineers. Walk through a real 22kW motor circuit from design current to voltage drop verification, with every number shown and every step explained.
Fuse vs MCB vs MCCB: Protection Device Selection for LV Industrial Distribution
Objective comparison of HRC fuses, MCBs, and MCCBs for LV industrial distribution. Fault breaking capacity, I2t energy let-through, discrimination, maintenance cost, and a decision matrix for each device type.
IEC 60364 vs NEC 2023: Key Philosophical Differences Every Engineer Should Know
IEC 60364 and NEC/NFPA 70 take fundamentally different approaches to electrical installation safety — prescriptive vs performance-based, different terminology, different cable sizing methods. These differences produce different cable sizes for the same load.
IEC 60909 vs ANSI/IEEE C37: Two Methods for Short-Circuit Calculation Compared
Side-by-side comparison of IEC 60909 and ANSI/IEEE C37 short-circuit calculation methods. Same 11kV fault scenario calculated both ways — showing where results diverge and why it matters for equipment specification.
IEC 61439 vs IEC 60439: What Changed for Panel Design [2026]
IEC 61439 replaces IEC 60439 — design verification vs type testing, 3 verification methods, temperature rise & short-circuit changes. Free guide for panel builders.
Manual Calculation vs ECalPro: Where Speed and Accuracy Actually Differ
An honest comparison of manual spreadsheet calculations versus ECalPro for cable sizing, voltage drop, and short-circuit work. Where software saves time, where manual methods still matter, and what neither approach replaces.
NFPA 70E 2024: 7 Arc Flash Changes + Compliance Guide [Free]
What changed in NFPA 70E-2024? 7 critical updates for PPE categories, arc flash boundaries, risk assessment & equipment labeling. Free compliance checklist.
Understanding Power Factor Correction: A Tutorial with Worked Calculations
Learn how to calculate capacitor bank sizing for power factor correction. Includes the power triangle, kVAR calculation, before-and-after current comparison, harmonic considerations, and IEC 60831 capacitor selection.
Protective Relay Coordination Tutorial: From Fuse-MCCB-Relay Chain to a Full Coordination Chart
Step-by-step tutorial on building a time-current coordination chart for a three-level protection system. Covers TCC reading, discrimination margins, relay settings, and common coordination failures.
How to Read a Cable Sizing Table (AS/NZS 3008 Table 13 Explained)
Learn exactly how to navigate AS/NZS 3008.1.1:2017 Table 13 for cable current ratings. Step-by-step guide covering installation methods, insulation types, conductor formations, and common mistakes.
IEC 60909 Short-Circuit Calculation: Step-by-Step Walkthrough
Complete IEC 60909-0 short-circuit calculation walkthrough. 11kV/415V transformer, 30m cable, every impedance correction factor. Free calculator included.
TN-S vs TT Earthing: A Real Cost and Safety Comparison for Remote Industrial Sites
Practical comparison of TN-S and TT earthing systems for remote and mining sites. Installation cost, protection reliability, touch voltage analysis per IEC 60364-4-41, and real lessons from high-resistivity soil conditions.
How to Size a Cable for a VFD-Driven Motor: Step-by-Step with IEC 60364
VFD output cables carry harmonic-rich currents that standard sizing tables don't account for. Learn how to apply harmonic derating, manage cable capacitance, and correctly size a VFD-to-motor cable per IEC 60364-5-52.
Voltage Drop Calculation: 3 Methods Compared [Worked Example]
Compare simplified, mV/A/m, and full impedance voltage drop methods on the same circuit. See where simplified breaks down. Free calculator + IEC 60364 limits.
XLPE vs EPR vs PVC Cable Insulation: Which to Specify for High-Temperature Industrial Plants
A data-driven comparison of XLPE, EPR, and PVC cable insulation for industrial plant applications. Temperature ratings, chemical resistance, fire performance, bend radius, and cost per metre — all referenced to IEC 60502-1.
The 125% Rule: When NEC Motor Sizing Creates Oversized Cables
NEC 430.22 requires 125% of FLC for continuous duty motors. Combined with conservative derating, cables end up 2-3 sizes larger than needed. Here's the cost of oversizing and how IEC does it differently.
Why Your Arc Flash Labels Are Already Wrong: The IEEE 1584-2018 Update Most People Missed
IEEE 1584-2002 used a simplified model. The 2018 edition introduced 5 electrode configurations — same equipment, same fault current, but incident energy changes by 300%+. Are your labels still based on 2002?
Neutral Sizing: The Hidden Third Harmonic Problem Nobody Calculates
In balanced 3-phase systems, engineers assume neutral current is zero. With LED lighting and SMPS loads, 3rd harmonic currents ADD in the neutral — reaching 173% of phase current. Here's the calculation most designs miss.
Short Circuit Ratings: The Cable Nobody Checks (Until It Fails)
Most engineers size cables for ampacity and voltage drop. The adiabatic equation (k²S² ≥ I²t) is often forgotten. Here's a real scenario where a properly-sized 4mm² cable fails at 16kA — and how to check yours.
Your Voltage Drop Calculation Is Wrong — The Reactance Error
Why mV/A/m voltage drop is wrong for cables ≥95mm². Reactance dominates above 50m — and at 0.8 PF, voltage drop is LESS than unity PF. Free calculator inside.
Cable Pulling Calculations for Mining — Lessons from 18 Years Underground
Mining cable pulls face unique challenges: steep declines, high ambient temperatures, confined spaces, and zero margin for error. Practical lessons from underground operations.
Cable Pulling Physics — Why Every Bend Multiplies Tension (Capstan Equation)
Understand the capstan equation and why cable pulling tension multiplies at every bend. Real field examples from 18+ years in mining. Free engineering guide.
Why Aluminium Cables Are Making a Comeback — And When They're Actually Better Than Copper
Copper prices have tripled since 2020. At 185mm² and above, aluminium cables deliver the same performance at 40-60% less cost. Here's the engineering case for aluminium that most specs ignore.
Arc Flash Isn't Just an American Problem: Why Every LV Switchboard Needs an Assessment
Engineers outside the US think arc flash is an 'American requirement.' Wrong. A 400V 25kA switchboard produces 8-15 cal/cm² — enough for third-degree burns in 0.1 seconds.
AS/NZS 3008:2025 vs 2017 — 7 Changes That Affect Every Cable Calculation
The new AS/NZS 3008.1.1:2025 replaces the 2017 edition with significant changes to DC cable ratings, installation methods, and derating tables. Here are 7 changes every Australian and NZ engineer must know.
BS 7671 vs IEC 60364: Same Origin, Different Paths — And Why It Matters for Your Calculations
BS 7671 and IEC 60364 share a common ancestor but diverge on cable sizing, earth fault protection, and installation methods. These differences change your calculation results significantly.
The Grouping Factor Trap: Why 6 Cables in a Tray Don't Always Derate by 0.57
Engineers blindly apply grouping factors from Table C.9/Table 22. But the actual derating depends on cable utilisation — and most engineers don't know this shortcut can save them 2 cable sizes.
Operating Temperature vs Maximum Temperature: The Cable Rating Nobody Checks
Your 4mm² cable is rated at 32A — but only at exactly 70°C conductor temperature. At 40°C ambient instead of 30°C, it's actually 28A. Here's the thermal calculation most engineers skip.
Cable Sizing Guide: BS 7671, IEC 60364, NEC & AS/NZS [Free]
Size cables per BS 7671, IEC 60364, NEC, and AS/NZS 3008. Step-by-step methodology with worked examples. Free online calculator — no signup required.
Why Your Cable Sizing Is Wrong: The Reactive Component Most Engineers Ignore
Most engineers calculate voltage drop using resistance only. Above 25mm², the reactive component can add 15-30% more voltage drop. Here's what you're missing.
The Conduit Fill Calculation Everyone Gets Wrong — And Why NEC Chapter 9 Is More Complex Than You Think
1 wire = 53%, 2 wires = 31%, 3+ wires = 40%. Easy, right? Wrong. Equipment grounding conductors, nipples, cable assemblies, and mixed sizes all have different rules.
Why Your Earth Electrode Resistance Test Passes — But Your Earthing System Fails
You drove a rod, tested at 5Ω, and moved on. But electrode resistance changes with seasons — a 5Ω reading in the wet season can be 50Ω in the dry. One test doesn't validate your earthing system.
Earth Fault Loop Impedance: The Calculation That Determines If Your RCD Actually Protects
Installing an RCD doesn't guarantee protection. If your earth fault loop impedance is too high, the fault current won't reach the trip threshold. Here's how to verify your protection actually works.
The Difference Between kW, kVA, and kVAr — And Why Getting It Wrong Costs You 20% More Cable
Engineers who size cables using kW instead of kVA consistently undersize by 15-25%. A 100kW motor at 0.85 PF draws 118kVA — and that's the number your cable must carry. Here's why this matters.
Maximum Demand Calculation — Diversity Factors Explained Step-by-Step
Calculate maximum demand with diversity factors in 3 steps. Covers AS/NZS 3000, IEC 60364 & NEC Article 220 methods. Free calculator included.
Voltage Drop at Startup vs Running: The Motor Circuit Calculation Engineers Forget
Your cable passes the 5% running voltage drop test. But at motor startup with 6-8× inrush current, voltage drop hits 25-40%. The motor stalls, contactors drop out, and VFDs fault. Here's the calculation nobody does.
The 80% NEC Rule That Doesn't Mean What You Think
Engineers say 'the NEC 80% rule' but most don't understand WHERE the 80% comes from, WHEN it applies, and WHY it's different from derating. This article clears up the most misunderstood NEC requirement.
Neutral Current in Three-Phase Systems: The Harmonic Problem Nobody Talks About
In a balanced 3-phase system, neutral current should be zero. With modern LED lighting and switch-mode power supplies, neutral current can EXCEED phase current. Here's why your neutral is overloaded.
Parallel Cables Don't Share Current Equally — And Here's When That Destroys Your Installation
You installed 2 × 185mm² in parallel to carry 400A. But one cable carries 250A while the other carries 150A. The overloaded cable overheats and fails.
Protection Discrimination: Why Your MCB Trips Instead of the Fuse
You have a 63A fuse upstream and a 20A MCB downstream. A fault occurs — and the 63A fuse blows instead of the 20A MCB. Here's why protection discrimination fails more often than engineers think.
Short Circuit Calculations: The 3 Numbers Every Engineer Must Know Before Specifying a Switchboard
Engineers specify switchboards without knowing the prospective fault current. If a 25kA-rated board sees 35kA, bus bars weld together. Here are the 3 numbers you MUST calculate first.
Solar PV String Sizing: Why Your Inverter Clips at 2pm on the Hottest Day
You sized your PV strings at STC (25°C). But on a cold morning, Voc jumps above the inverter maximum. On a hot afternoon, Vmp drops below MPPT range. Here's the temperature calculation.
Transformer Sizing: Why kVA Rating Alone Doesn't Tell You If Your Transformer Is Adequate
You matched the load to the kVA rating. But impedance, tap range, vector group, inrush current, and harmonic loading all determine whether the transformer actually works in your system.
AS/NZS 3008:2025 — What Engineers Need to Know
Overview of key changes in AS/NZS 3008.1.1:2025 compared to the 2017 edition. Covers updated current rating tables, new cable types, revised derating factors, IEC harmonisation, solar PV cable provisions, and transition timeline.
BS 7671 Amendment 4 Is Coming in April 2026 — Here's What Changes for Practising Engineers
A practical guide to BS 7671:2018 Amendment 4 (April 2026). Covers expanded AFDD requirements, EV charging circuit minimums, PV chapter rewrite, transition period rules, and what practising UK electrical engineers need to update in their design workflow.
What Grenfell Tower Taught the Electrical Industry About Cable Specification
An analysis of the cable specification lessons from the Grenfell Tower fire. Covers fire performance classification under BS EN 60332 and IEC 60332, the gap between minimum compliance and fit-for-purpose cable selection, and why fire performance should be a first-class parameter in every cable sizing decision.
AS/NZS 3008.1.1:2025 Just Dropped — ECalPro Is the First Cloud Platform to Implement It
ECalPro is the first cloud-based electrical calculation platform to implement the AS/NZS 3008.1.1:2025 cable sizing tables. Learn what changed in the 2025 edition, why legacy tools like jCalc and ELEK still reference 2017 tables, and how to run a 2025-compliant calculation today.
Five Reasons Your Excel Cable Sizing Spreadsheet Will Fail a Technical Audit
After 15 years of reviewing cable sizing spreadsheets, the same five failure patterns appear in every technical audit. This article explains why Excel-based cable sizing consistently fails independent review and what to use instead.
Piper Alpha and the Cost of Not Coordinating Your Protection System
An analysis of the protection coordination lessons from the 1988 Piper Alpha disaster. Covers how permit-to-work failures intersect with electrical protection design, why coordinated vs non-coordinated protection systems matter, and why current transformer isolation (CTI) is critical even on small LV systems.
IEEE 1584-2018 vs 2002 — The Changes That Add Up to Completely Different Results
A detailed comparison of IEEE 1584-2018 and the 2002 edition, covering the five electrode configurations, enclosure geometry corrections, gap distance as a real variable, and why arc flash labels calculated under the old model may be dangerously inaccurate.
Voltage Drop Limits Around the World — Why 3% in the UK Is Not the Same as 5% in Australia
An international comparison of voltage drop limits across NEC (3%), IEC 60364 (4%), AS/NZS 3000 (5%), and BS 7671 (split limits). Explains measurement origin differences, practical implications, and why applying the wrong standard to the wrong country produces undersized cables.
Power Factor Correction Capacitors Can Make Your Harmonics Problem Worse
How power factor correction capacitors interact with harmonic currents to create resonance conditions, why the 5th harmonic is the worst offender, and how detuned reactors solve the problem. Includes the resonance frequency formula and practical sizing guidance.
Every Number on a Motor Nameplate Explained — And Why They All Affect Your Cable Size
A practical guide to reading motor nameplates: kW rating, service factor, power factor, efficiency class (IE2/IE3/IE4), duty cycle classes S1-S9, and how each parameter flows into cable sizing, protection settings, and starter selection.
Cloud vs Desktop Electrical Calculation Software — The Honest Comparison for 2026
An honest comparison of cloud-based and desktop electrical engineering calculation software in 2026. Covers total cost of ownership, collaboration, standards currency, where desktop still wins (large network simulation, SLD), and where cloud wins (access, PPP pricing, instant updates).