SE Stephens Engineering Group
Electrical & Building Services Consultancy

Electrical design authority for commercial and public buildings.

Senior-led design, compliance and technical review. Where you want one point of responsibility, we manage the works through to certification.

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Coverage
South Wales · Bristol · UK Wide
Established
2025
Scope
Design · Compliance · Certification
Direct
07478 269752
What we do

Consultancy first. Delivery when you need it.

Electrical Design

LV distribution, small power and critical power. Part L and decarbonisation strategy. RIBA Stage 0 to 4 packages.

Lighting Design

Architectural, functional and emergency lighting. DALI-2 controls and Dialux modelling.

PV & EV

Array design and yield, charge point load management, DNO and G99 applications.

Compliance & Technical Review

Condition surveys, asset registers, prioritised remedial plans and contractor scope review.

Handover & Assurance

Certificate tracking, as-built checks and O&M review.

Where a single point of responsibility suits the project, SEG manages installation through an approved contractor and retains design authority through to certification.

How we’re engaged

Design

Drawings, specification and schedules issued for tender.

Design and managed works

SEG designs, oversees the installation and issues certification.

Independent review

Buildability and compliance review of a third-party design.

Selected work

Drawn properly.

SOLAR PV ARRAY Single line diagram 46.35 kWp 40 kW inverter / 7 strings / 4 MPPT MPPT 1 : 1.1 STRING OF 18 x TRINA 450W (TSM-450NEG9R.28) MPPT 1 : 1.2 STRING OF 18 x TRINA 450W (TSM-450NEG9R.28) MPPT 2 : 2.1 STRING OF 10 x TRINA 450W (TSM-450NEG9R.28) MPPT 2 : 2.2 STRING OF 10 x TRINA 450W (TSM-450NEG9R.28) MPPT 3 : 3.1 STRING OF 16 x TRINA 450W (TSM-450NEG9R.28) MPPT 3 : 3.2 STRING OF 19 x TRINA 450W (TSM-450NEG9R.28) MPPT 4 : 4.1 STRING OF 12 x TRINA 450W (TSM-450NEG9R.28) SOLIS 40K 5G 3P QUAD MPPT INVERTER AC ISO AC ISOLATOR kWh GENERATION METER EXISTING LV BOARD CAT5 CT LINK PV ARRAY TABLE STRING MODULES KWP 1.1 18 8.10 1.2 18 8.10 2.1 10 4.50 2.2 10 4.50 3.1 16 7.20 3.2 19 8.55 4.1 12 5.40 TOTAL 103 46.35 SYSTEM DESIGN PARAMETER VALUE Peak power 46.35 kWp Inverter power 40 kW Modules 103 x Trina Solar 450W Module type TSM-450NEG9R.28 Inverter Solis 40K 5G, 3P quad MPPT Standards BS 7671 / BS EN 62446 / G99
Solar PV · Single line diagram 46.35 kWp rooftop array, 103 modules, 40 kW inverter, metered into the existing LV board.
SEG-SLD-DALI-001 DALI-2 LIGHTING CONTROL ARCHITECTURE STAGE 2 CONCEPT - NOT FOR CONSTRUCTION SYSTEM ARCHITECTURE BMS HEAD END BACnet/IP [1] IP BACKBONE AC-GF Ground floor DALI-2 application controller AC-01 Level 1 DALI-2 application controller AC-02 Level 2 DALI-2 application controller AC-RF Roof and external DALI-2 application controller TYPICAL FLOOR - LINE ARCHITECTURE (AC-01 shown, AC-GF and AC-02 identical) AC-01 2 x 4-line router 8 lines fitted, 6 used 25% spare per I-17 [2] PSU 250mA D1 Open plan - perimeter zone A 56 luminaires | 6 sensors | 0 panels | 62 addresses | 124mA PSU 250mA D2 Open plan - perimeter zone B 56 luminaires | 6 sensors | 0 panels | 62 addresses | 124mA PSU 250mA D3 Open plan - interior zone 55 luminaires | 6 sensors | 2 panels | 63 addresses | 126mA PSU 250mA D4 Cellular and meeting rooms 43 luminaires | 10 sensors | 8 panels | 61 addresses | 122mA PSU 250mA D5 Circulation and stairs 57 luminaires | 6 sensors | 0 panels | 63 addresses | 126mA PSU 250mA D6 WC, tea point, plant, store 30 luminaires | 8 sensors | 4 panels | 42 addresses | 84mA TYPICAL LINE DETAIL - D1 DALI bus LUM L1 x 56 LUM SEN presence + SEN daylight x 6 EM L7 self-test EM PNL wall panel LUM Bus is polarity free, 2-core 1.5mm2 rated 300/500V, max 300m per line, 2V max drop. It may share a multicore with the mains supply because it is mains-rated - but it is NOT SELV and must never be treated as Band I [3]. CONTROL STRATEGY Ref Space Detection Daylight Standby Off K-01 Open plan - perimeter Presence Closed loop dimming Dim to 10% 20 min K-02 Open plan - interior Presence None Dim to 10% 20 min K-03 Cellular and meeting Absence Closed loop dimming Off 15 min K-04 Circulation Presence Open loop where glazed Dim to 20% 10 min K-05 Stairs Presence None Dim to 20% 10 min K-06 WC Presence None Off 10 min K-07 Plant and store Presence None Off 15 min K-08 External and EV area Photocell Dusk to dawn Dim to 30% after 23:00 - Absence detection in cellular rooms is deliberate - manual on, auto off. LINE LOADING Line Addr Max Spare mA Chk D1 62 64 3% 124 PASS D2 62 64 3% 124 PASS D3 63 64 2% 126 PASS D4 61 64 5% 122 PASS D5 63 64 2% 126 PASS D6 42 64 34% 84 PASS KEYNOTES [1] BMS interface is BACnet/IP at the application controller, not at device level. Exposing 350 DALI addresses to the BMS creates a maintenance problem nobody wants to own. [2] Two 4-line routers per floor gives 8 lines against 6 used. Spare lines matter more than spare addresses - a line at 63 of 64 addresses is effectively full. [3] The DALI bus is mains-rated and may share containment with the supply, but it is not SELV. Treating it as Band I is a common and expensive error at installation. [4] Emergency luminaires are DALI-2 Part 202 self-test on the same lines as general lighting. Monthly function and annual duration tests are logged automatically to BS EN 50172:2024. [5] Commissioning is where DALI projects fail. Addressing, grouping and scene setting must be a named deliverable with a witnessed handover, not something the installer does on the last Friday. [6] Sensor current is taken as 2mA. Some multi-sensors draw considerably more - verify against actual device data before the line allocation is frozen. STEPHENS ENGINEERING GROUP SEG DALI-2 lighting control architecture Reference building, LV distribution design standard DRG No SEG-SLD-DALI-001 REV P01 SCALE NTS @ A3 STATUS STAGE 2 CONCEPT - NOT FOR CONSTRUCTION Do not scale. Read with SEG-SCH-LVD-001 sheet 13 and SEG-REF-LTG-002.
Lighting control · DALI-2 architecture Reference design standard. BACnet/IP backbone, six lines per floor, each checked against the 64-address limit.
Who we work with

Technical input with a defined scope.

  • Architects and developers
  • Building surveyors
  • Electrical and main contractors
  • Landlords and property owners
About

Senior engineering input from the first conversation.

Founded by Aaron Stephens MIET, SEG is an electrical and building services consultancy based in Newport, working across South Wales, Bristol and the UK.

Every project is led at senior level, with Part L and decarbonisation built in from the start.

Contact

Discuss a project.

Send drawings, a brief or an idea.

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