Commercial Electrical
Contractor Mid Somerset

TPN Distribution & Balanced Loading

Every three-phase installation starts with a maximum demand calculation. We assess every load on the premises -- machinery, HVAC, lighting, socket circuits, kitchen equipment -- and calculate total demand in kVA across all three phases. This determines your incoming supply size and ensures balanced loading across L1, L2, and L3 to prevent neutral overloading and voltage imbalance.

We install TPN (Triple Pole and Neutral) distribution boards with careful phase allocation. Single-phase loads distributed evenly across the three phases to maintain balance within 10-15% -- critical for motor longevity and power quality. Three-phase loads such as compressors, large HVAC units, and industrial machinery connected directly through TP isolators with appropriate overload protection.

• Maximum demand calculations to BS 7671 and IET Guidance Note 1
• DNO application management (WPD/National Grid) for new or upgraded supplies
• Phase rotation verification for motor-driven equipment
• CT metering for landlord/tenant sub-metering and energy monitoring
• Power factor correction where reactive loads (motors, VFDs) reduce efficiency

What We Install

From a new 100A three-phase supply for a small workshop to a 400A+ supply feeding an industrial unit, we handle the complete process: DNO liaison, meter position, main switch, distribution, sub-mains, and final circuits. Every installation designed with diversity applied correctly and fault levels calculated to ensure protective devices operate within disconnection times.

• New three-phase supplies -- 60A to 400A+
• Single-phase to three-phase upgrades
• Sub-main distribution to multiple areas or floors
• Automatic changeover switches for generator backup
• Harmonic filtering where non-linear loads create power quality issues

Protection Strategy

RCBO vs MCB+RCD: For commercial installations, we specify individual RCBOs on critical circuits. Each circuit gets its own overcurrent and earth leakage protection, so a single fault does not trip an entire bank -- essential where loss of power to refrigeration, servers, or EPOS means lost revenue.

Where budget requires it, we use split-load boards with MCBs protected by upstream RCDs -- but always with careful circuit grouping so a trip on one RCD does not take out both lighting and power in the same area.

RCD Types & Protection

Type A RCDs detect sinusoidal AC earth leakage and pulsating DC fault currents. Required by BS 7671 for circuits feeding IT equipment, LED drivers, and EV chargers.

Modern EV chargers (Hypervolt, Ohme, Zappi, Easee) have integral 6mA DC fault detection, so Type A RCBOs on the supply side are correct for every domestic and commercial install we carry out. Type AC alone is no longer acceptable under the 18th Edition.

Surge Protection (SPD)

Type 1+2 SPDs installed at the origin of supply protect against direct lightning strikes and indirect surges. BS 7671 requires a risk assessment for SPD provision on every new installation -- for commercial premises, the answer is almost always yes.

We install SPDs with backup fuse protection and short cable runs to the main earth bar. Type 3 SPDs added at point-of-use for sensitive equipment such as server rooms and medical devices.

Boards We Specify

• Hager -- Invicta 3 TPN boards, reliable and widely stocked, our go-to for most commercial work
• Schneider Electric -- Acti9 iC60 range for premium installations and client specification
• ABB -- System pro E power for larger industrial switchgear

Every Board Includes

• Full circuit schedule with descriptions, device ratings, cable sizes
• Warning labels, isolation procedures, danger notices to BS 7671
• Spare ways for future expansion (minimum 20% spare capacity)
• IP-rated enclosures (IP65 washdown, IP54 plant rooms)

Cable Types We Use

• SWA (Steel Wire Armoured) -- external runs, underground routes, anywhere needing mechanical protection. Glanded with CW glands and earthed via the armour
• LSOH (Low Smoke Zero Halogen) -- mandatory for public buildings, schools, hospitals, premises with sleeping accommodation. Minimal toxic smoke in fire
• FP200 (Fire Performance) -- fire alarm and emergency lighting circuits. Maintains integrity during fire. BS 5839-1, BS 5266, BS 8491, BS EN 50200
• Cat6 / Cat6a -- structured data cabling. Cat6: 1Gbps at 100m. Cat6a: 10Gbps at 100m. Installed to TIA-568 with cable tester certification
• Fibre Optic -- OM3/OM4 multimode for building backbone, OS1/OS2 singlemode for campus links. Fusion spliced, OTDR tested

Containment Systems

Properly specified containment protects cables, simplifies future maintenance, and ensures fire stopping compliance.

• Galvanised trunking -- main cable routes through ceiling voids and risers
• Basket tray -- open mesh for data cabling, excellent ventilation
• Ladder rack -- heavy-duty for sub-main cables and SWA in plant rooms
• Steel conduit -- surface-mounted in exposed areas, workshops, kitchens
• PVC conduit -- concealed wiring in walls and ceiling voids

System Types

Self-contained units have individual batteries within each luminaire. Most common for smaller premises -- each unit independent. Typical battery life 3-4 years.

Central battery systems use a single battery bank feeding all emergency luminaires via FP200 fire-rated cable. Better for large premises -- easier to maintain, longer battery life, consistent output.

Maintained vs Non-Maintained: Maintained fittings illuminate at all times, switching to battery on mains failure -- required in cinemas, theatres, entertainment venues. Non-maintained only illuminate on mains failure -- standard for offices, shops, most commercial buildings.

Testing & Certification

BS 5266 mandates a strict testing regime. We provide testing contracts and issue emergency lighting certificates.

• Monthly flash test -- brief mains failure simulation confirming each luminaire works. Recorded in log book
• Annual 3-hour duration test -- full discharge confirming rated illumination. Failures replaced
• Emergency lighting certificate issued after each annual test
• Lux level verification at floor level (min 1 lux centre line, 0.5 lux band)
• Coverage of all exit routes, direction changes, stairwells, fire fighting equipment, final exits

System Categories

BS 5839-1 categories determine detection coverage, set by the fire risk assessment:

• Category L1 -- detection throughout entire building including roof voids. Highest life protection. Care homes, HMOs, high-risk
• Category L2 -- detection in areas where fire could threaten escape routes. Common in offices. Escape routes plus adjacent rooms plus high-risk rooms
• Category L3 -- escape routes only. Corridors, stairways, landings
• Category L4 -- escape routes only. Minimum level for life safety

Conventional vs Addressable

Conventional divides into zones -- panel shows which zone, not which detector. Good for smaller premises.

Addressable gives every device a unique address. Panel identifies exact detector location. Essential for larger buildings.

Cause and effect: specific detectors trigger specific actions. Kitchen detector = local sounder only. Server room = HVAC damper shutdown. Fire doors release by zone.

• Weekly testing -- different call point each week, recorded in log book
• Six-monthly service to BS 5839-1
• Fire alarm certificate on commissioning and after every service

Periodic Inspection (EICR)

Commercial premises need an EICR every 5 years minimum. Legal requirement under the Electricity at Work Regulations 1989.

• Full inspection and testing from origin to furthest point of every circuit
• Distribution board schedules verified and updated
• Thermal imaging for loose connections and overloaded circuits
• Loop impedance, insulation resistance, RCD trip times recorded
• C1, C2, C3, FI observations coded and explained in plain English

Planned Preventive Maintenance (PPM)

Scheduled visits to inspect, test, service, and maintain your entire electrical installation. No unexpected downtime.

• Quarterly, six-monthly, or annual visit schedules
• Emergency lighting tests and fire alarm servicing included
• PAT testing on a risk-based schedule
• Emergency callout SLA -- 4-hour critical, same-day non-critical
• All compliance documentation maintained and current

Offices

Cat A/B fit-outs, desk power, data, lighting

Retail

Display lighting, EPOS, security systems

Restaurants & Pubs

Kitchen circuits, extraction, bar lighting

Hotels & B&Bs

Room circuits, maintained emergency lighting

Warehouses & Factories

Three-phase, high bays, machinery power

Schools & Education

LSOH cabling, safeguarding, ICT suites

Churches & Heritage

Sympathetic installations, listed buildings

Landlords & Agents

EICRs, compliance, tenant changeovers

Data Centres & Comms

UPS, PDUs, rack power, structured cabling

GP Surgeries & Dental

Clean-power circuits, treatment-room lighting, CQC-compliant emergency systems