Commercial & workplace EV charging installation

Client brief and scheme planning

Commercial EV work is an infrastructure project. The Code of Practice expects a documented design stage before any cable is pulled.

• Use case — workplace staff parking (long dwell, low power), fleet/depot (overnight, high aggregate load), customer/retail (short dwell, higher power), destination or public charging (payment, uptime and accessibility obligations).
• Number of charge points now, and the cabled/ducted provision for future expansion — installing spare ducts and a sized supply at first fit is dramatically cheaper than a second dig.
• Power profile — 7 kW and 22 kW AC, or 50 kW+ DC rapid. Aggregate simultaneous demand drives the whole design.
• Ownership and operation — who holds the maintenance obligation, who handles billing/back office, and who is the responsible person for periodic inspection.
• Planning, landlord consent, wayleaves and easements where cabling crosses land not in the client's control.
• Building Regulations Part S (England) — new non-residential buildings and major renovations have minimum charge point and cable-route requirements; confirm what applies before design freeze.
• Accessibility — PAS 1899 guidance on accessible charge points: bay dimensions, kerb transitions, connector weight and height, and clear approach.

Supply, DNO and pre-installation checks

• Confirm the incoming supply: LV single/three phase, or HV with the client's own transformer and switchgear. Record the earthing arrangement, transformer rating, and the main switchboard's spare capacity.
• Measure Ze and Ipf at the intake and at the proposed distribution point — breaking capacities on commercial boards can be much higher than domestic.
• Maximum demand assessment for the whole site, with recorded data where available: a half-hourly metering download over a representative period beats a paper calculation.
• Engage the DNO early. New or increased capacity connections (ENA G100/G99 arrangements where storage or generation is involved) have long lead times, and the connection offer often decides the scheme's power level.
• Where capacity is limited, present load management as the alternative to reinforcement — G100 export/import limiting schemes and dynamic load balancing across the charger cluster.
• Above 60 A per phase — once the maximum demand assessment has been calculated with the new charge point(s) included and the result exceeds 60 A, the DNO must be informed before the installation proceeds to ensure compliance with their connection arrangements. This applies equally where load limiting is the chosen answer: a load curtailment scheme that caps charging to keep demand within the supply must be agreed with the DNO under an ENA G100 arrangement, not fitted unilaterally. Record the DNO's response — connection approval, G100 agreement, or a reinforcement offer — in the job file.
• Existing installation condition — an EICR or targeted survey of the distribution serving the new load, including protective bonding, earthing conductor sizes and switchgear condition.
• Fault level study where new distribution boards or sub-mains are added, to confirm device ratings remain adequate.
• Metering strategy — sub-metering per charger or per cluster for recharging costs, and MID-compliant meters where energy is resold.

Earthing, PME and TT arrangements

The open-PEN problem is the same as domestic, but the scale changes the practical answer. Reg 722.411.4.1 still governs.

• PME earthing must not be exported to vehicle chassis unless an open-PEN detection device is used or a TT arrangement is provided.
• On multi-point car parks, a single earth-mat/electrode TT island serving the charging installation is often more practical than device-level open-PEN, and gives a consistent measurable Ra.
• Where a TT island is created, maintain separation from PME earthed metalwork (lighting columns, barriers, structural steel) — simultaneous contact must be prevented, and the separation distance must be assessed and recorded.
• In car parks with extraneous metalwork, carry out a full assessment of extraneous-conductive-parts and bonding; bonding structural steel back to a TT island defeats the purpose.
• HV-supplied sites with their own substation may have a combined or segregated earthing arrangement — an earthing study (ENA TS 41-24 principles) is required before treating it as TN-S.
• Document the earthing arrangement clearly at the distribution board with warning notices, so future contractors do not cross-bond systems.

Distribution and circuit design

• Dedicated final circuit per connection point (722.55.101) — no shared final circuits, no daisy-chained sockets.
• 30 mA RCD protection per connection point, with DC fault management: Type B RCD, or Type A plus 6 mA DC detection integral to the equipment.
• Dedicated charger distribution board(s) close to the cluster, fed by a sized sub-main, with a clearly labelled local means of isolation and emergency switching where required.
• Three-phase 22 kW AC units — balance the phases across the cluster, and consider phase rotation for units that can single-phase fall back.
• DC rapid chargers — typically 50 kW to 350 kW, often supplied as a packaged unit with its own internal protection; the installer's scope is supply, earthing, foundation, containment and coordination with the manufacturer's commissioning.
• Diversity across a cluster is real but must be justified. Fleet depots charging overnight often have near-unity coincidence; workplace car parks do not. Do not borrow domestic diversity figures.
• Load management system: static limit, dynamic limit via CT metering at the intake, or an operator-controlled scheme. Specify failure mode — the system must fail to a safe, limited state.
• Selectivity/discrimination between the charger device, the sub-main device and the main incomer, so a single charger fault does not drop the site.
• Surge protection to Section 443/534 at the origin and, for long external runs, at the charger distribution board.
• Emergency switching and fire-service isolation — agree location and labelling with the responsible person; enclosed and underground car parks may attract additional fire-strategy requirements.

Cabling, containment and civils

• Size sub-mains for continuous duty and the full designed cluster load, with future expansion allowance where agreed.
• Voltage drop across long car-park runs is usually the binding constraint — check the furthest charge point, not the nearest.
• Buried cable: SWA at a minimum 500 mm (600 mm under roads/parking), marker tape, bedding sand, and ducting with draw ropes for future circuits.
• Ducting and chambers sized and positioned at first fit — spare ducts to unequipped bays are the cheapest part of the project.
• Segregation from other services (gas, water, telecoms) to the relevant utility spacing requirements, and full service searches/CAT scanning before excavation.
• Fire-stopping at every compartment penetration, and fire-rated support systems where cables cross escape routes.
• Charger foundations/plinths designed for the unit weight and impact protection (bollards, wheel stops, kerbs) — vehicle impact is the most common damage cause.
• Corrosion and IP/IK ratings suited to exterior coastal or exposed sites; stainless fixings and correctly sealed gland entries.
• Cable management on the units themselves — tethered leads kept off the ground, no trip hazards across pedestrian routes.

Inspection, testing and commissioning

• Full initial verification to Part 6: continuity, insulation resistance (isolating electronic equipment), polarity, Ze, Zs, Ipf, phase sequence, and functional testing of every switching and protective device.
• RCD testing appropriate to the device type — Type B testing needs an instrument capable of smooth DC and higher-frequency residual currents.
• TT installations — measure Ra at each electrode/mat and verify disconnection times; record the electrode arrangement.
• Verify open-PEN device operation by the manufacturer's stated method.
• Functional charging test per point, with an EVSE simulator or a real vehicle: CP/PP signalling, locking, current limit, RFID/payment start, and back-office reporting.
• Load management proving — simulate a high-demand scenario and confirm curtailment occurs before the intake limit is reached, plus the safe behaviour on comms loss.
• Electrical Installation Certificate with full schedules of inspection and test results; a Minor Works Certificate is never appropriate for this work.
• Building Regulations notification where applicable, plus any Part S evidence for the building control file.
• Handover pack — as-built drawings, schedules, duct records, manufacturer documentation, smart charge point statements of compliance, operating instructions, and the maintenance schedule.

Maintenance, periodic inspection and duty holder obligations

• The site operator is a duty holder under the Electricity at Work Regulations 1989 — the charging installation must be maintained in a safe condition.
• The Code of Practice recommends routine checks of charging equipment far more often than the fixed installation: visual checks of leads, connectors, enclosures and impact damage on a regular (often monthly) basis.
• Periodic inspection of the charging installation is typically recommended at intervals not exceeding 3 years for public and commercial equipment, or shorter where the environment or usage demands it — set the interval in the EIC and confirm at each inspection.
• Manufacturer servicing intervals for DC rapid units (filters, fans, cooling, contactors, firmware) must be diarised — these are not fit-and-forget assets.
• Tethered leads and connectors are consumable items; establish a replacement route and keep spares for high-use bays.
• Record keeping — inspection reports, fault logs, uptime data, and firmware/security updates required by the Smart Charge Point Regulations for workplace units.
• Incident and misuse management: reported shocks, repeated RCD operation, or impact damage must take the bay out of service until inspected.

Common failures to avoid

• Designing the cluster load with domestic diversity assumptions.
• Leaving DNO engagement until the chargers are on site.
• Exporting PME earthing into a car park with bonded structural steel.
• No spare ducts — the second phase costs more than the first.
• Voltage drop checked at the nearest bay only.
• No load-management failure mode defined, so a comms loss means full current.
• No maintenance schedule handed over, leaving the operator non-compliant from day one.
• Accessibility ignored — bays that no wheelchair user can actually use.