Skill Profile
Electrical Load Calculations
"The observable action of calculating the total electrical demand of a building or system — including connected loads, diversity factors, and future capacity — in order to correctly size cables, switchgear, protective devices, and supply infrastructure."
YOUR SKILLS
Problems This Skill Solves
- Undersized cables and switchgear that overheat under actual demand, creating fire risk and causing installation failures
- Supply infrastructure (transformers, incoming mains) that cannot meet peak load demand, causing voltage drop, tripping, and production downtime
- Over-specification of electrical infrastructure, wasting capital cost on oversized components when accurate load calculations would have indicated a smaller, cheaper solution
- Non-compliance with BS 7671 (IET Wiring Regulations) because cable sizing and protective device selection are not supported by documented calculation
Tools Used
"Load calculations are mainly about diversity factors — apply the right diversity, and the calculated demand reflects what the installation will actually draw."
Diversity factors reduce the connected load to an estimated maximum demand, but the calculation also needs to account for power factor correction, the contribution of non-linear loads to harmonic distortion, the effect of inrush currents on protective devices, and future load growth. Applying diversity to connected load without addressing these produces a calculation that is right on average but wrong at the moments that determine protection sizing and cable selection.
Research & Outlook
Electrical load calculation is becoming more complex and more important as buildings transition to electrification — replacing gas heating with heat pumps, integrating EV charging, installing battery storage, and connecting building-level generation. Accurate load forecasting is now central to both infrastructure investment decisions and grid connection negotiations with DNOs. The skills required are evolving from static load schedule calculation towards dynamic demand modelling and energy systems analysis.
See This Skill In Action
Watch a professional demonstrate Electrical Load Calculations in a real working environment — what it looks like, how it's applied, and why it matters.
Engineering / Electrical
Electrical Load Calculations
Also Known As
Growth Path
Can calculate the connected load for individual circuits, apply basic diversity factors from standard tables, and produce a simple load schedule for a domestic or small commercial installation. Understands the relationship between load, current, and cable rating under standard installation conditions.
Produces load schedules and cable sizing calculations for multi-storey commercial or industrial installations, applying correction factors for installation method, temperature, and grouping. Selects appropriately rated distribution boards, MCBs, and RCDs. Prepares BS 7671-compliant design documentation for building regulations submission.
Designs electrical supply infrastructure for large or complex sites — hospitals, data centres, manufacturing facilities — including high-voltage intake, transformer sizing, power factor correction, harmonic mitigation, and resilience design. Conducts power quality surveys and load flow analysis. Advises on demand management strategies and future EV or renewable integration capacity.
How to Practise
- 1.Build a load schedule from scratch for a simple commercial office — list all circuits, calculate connected VA for each circuit, apply diversity factors from BS 7671 Table 1B, and sum to maximum demand.
- 2.Work through the IET Guidance Note 1 (Selection and Erection) cable sizing examples to practise applying correction factors for installation method, ambient temperature, and grouping.
- 3.Use Amtech or an equivalent software tool to model a small installation and compare the software output to a manual calculation to understand where the tool applies assumptions.
- 4.Review a set of existing electrical drawings for a building and verify that the main distribution board is correctly rated for the load schedule shown.
How to Prove
- ·Electrical installation design calculations submitted as part of a building regulations Part P application or BS 7671 design package, signed by a competent person
- ·Completed load schedules produced as part of a tender or detailed design package, reviewed and approved by a senior engineer
- ·IET membership with demonstrated electrical design competency, or CIBSE membership for building services engineers
- ·DNO (Distribution Network Operator) supply application completed with documented maximum demand calculation accepted by the network operator