Electrical
Electrical services design
LV distribution, lighting, small power, fire alarm and life safety design to BS 7671:2018+A4:2026 for buildings across the UK.
- Discipline
- Electrical
- Typical timescale
- Stage 2 concept in 2 to 3 weeks; Stage 4 technical design typically 6 to 10 weeks
WHAT IT IS
Electrical services design covers the distribution of power through a building and the systems that depend on it: incoming supply and LV distribution, small power, lighting and emergency lighting, fire detection and alarm, and the containment that carries all of it.
Every electrical design SDE issues is prepared to BS 7671:2018+A4:2026, with calculations for load, cable sizing, volt drop, earth fault loop impedance and discrimination carried out and recorded rather than assumed.
SERVICES
Services in this discipline
Fire alarm and detection design
Fire detection and alarm system design to BS 5839-1:2025, with the system category agreed against the fire strategy.
LV distribution design
Low voltage distribution design including maximum demand, cable sizing, volt drop, earth fault loop impedance and discrimination.
Lighting and emergency lighting design
Interior, exterior and emergency lighting design to BS EN 12464-1:2021 and BS 5266-1:2025, with calculated illuminance, glare and uniformity.
Security systems design
Access control, intruder alarm and CCTV design — zoning, containment and interfaces resolved with the fire and escape strategy.
Small power and data design
Small power layouts and structured cabling design — final circuits, containment, comms rooms and the loads a fit-out actually draws.
Utilities and renewables design
Incoming supply applications, substation and metering requirements, and PV, battery storage and EV charging design and connection.
WHEN YOU NEED IT
As early as Stage 1 on any project where the incoming supply capacity is in question. A supply upgrade from the distribution network operator has a lead time measured in months and occasionally in years, and it is the single most common cause of a services-driven programme delay.
Also on any new build, fit-out, refurbishment, change of use, or where an existing installation has reached the point that periodic inspection is recording unsatisfactory results.
OUR PROCESS
Load assessment and supply
Maximum demand assessed with diversity applied to the actual load profile. Incoming capacity confirmed against the DNO record early, because this is where programmes are lost.
Distribution design
Board positions, submain routes, cable sizing to BS 7671 with volt drop and earth fault loop impedance calculated, protective device selection and discrimination study.
Lighting and life safety
Lighting design to the illuminance and glare criteria for the task, emergency lighting to BS 5266, and fire detection and alarm to BS 5839-1 with the category agreed with the fire strategy.
Technical design and site
Full drawings, schedules and specification for tender and building warrant, then submittal review, inspection and witnessing through construction and handover.
DELIVERABLES
What you receive
- Maximum demand and diversity assessment
- LV distribution schematics
- Cable sizing, volt drop and earth fault loop impedance calculations
- Discrimination and protective device study
- Lighting design with calculations
- Emergency lighting design and drawings
- Fire alarm design to the agreed category
- Containment layouts and coordinated drawings
- Specification for tender
STANDARDS
Standards applied
The editions in force at the time of design. Where a standard is amended mid-project we confirm which edition the appointment is based on.
- BS 7671:2018+A4:2026Requirements for Electrical Installations — IET Wiring Regulations, 18th EditionIET
- BS 5266-1:2025Emergency lighting — code of practice for the emergency lighting of premisesBSI
- BS 5839-1:2025Fire detection and fire alarm systems for buildings — code of practice for designBSI
- BS EN 12464-1:2021Light and lighting — lighting of work places — indoor work placesBSI
- Approved Document BFire safety (England)GOV.UK
- Approved Document SInfrastructure for charging electric vehicles (England)GOV.UK
- Technical Handbook Section 4Safety (Scotland)Scottish Government
- IET Guidance Note 3Inspection and TestingIET
QUESTIONS
Common questions
What does an electrical services designer produce?
An electrical services designer produces the load assessment, distribution schematics, cable and protective device calculations to BS 7671, lighting and emergency lighting design, fire alarm design, containment layouts, drawings, schedules and a specification suitable for tender and for building warrant or Building Regulations approval.
Which edition of the Wiring Regulations do you design to?
BS 7671:2018+A4:2026, the consolidated 2026 edition of the IET Wiring Regulations published on 15 April 2026. BS 7671:2018+A2:2022+A3:2024 is withdrawn on 15 October 2026, and any design issued during the transition states on its face which edition it was assessed against. Where an amendment is published mid-project, the edition the appointment is based on is confirmed in writing so there is no ambiguity at handover.
How early do I need to check the incoming electrical supply?
At RIBA Stage 1 if there is any doubt. A supply upgrade from the distribution network operator has a lead time measured in months, and an unconfirmed supply capacity is the most common services-driven cause of programme delay on a construction project.
Do you provide electrical designs for building warrant applications?
Yes. Electrical designs are prepared to a standard suitable for submission with a building warrant application in Scotland, or for Building Regulations approval in England and Wales, including the calculations and drawings the verifier will expect to see.