3-Phase Distribution Boards for Commercial EV Charging UK

🏢 Commercial EV Charging · TPN Distribution · 3-Phase

3-Phase Distribution Boards for Commercial EV Charging UK

When a commercial site needs 5 or more EV charger circuits, individual protection boards for each charger stop making sense. A TPN (three-pole and neutral) distribution board provides centralised 3-phase power distribution, a single point of isolation, and a scalable foundation for any size commercial charging installation.

Covers: car parks · workplaces · hospitality · fleets · 5–50+ charger sites · 125A main switch
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Direct Answer

A TPN (Three-Pole and Neutral) distribution board distributes 3-phase power from the main supply to multiple EV charger circuits. Each circuit gets its own RCBO; the TPN board provides the main switch, surge protection, and a single point of isolation for the whole installation. EcoHarmony’s 125A TPN board with 4-pole main switch and SPD option is the standard specification for commercial EV charging sites with 5+ chargers.

5+ charger sites 125A 4-pole main switch TPN distribution board SPD option Car parks & workplaces Fleet charging infrastructure
🏠 Plain English — What is a TPN distribution board and why does it matter?

Think of a TPN distribution board as the electrical equivalent of a motorway junction. The main supply arrives at the board — at 125A across three phases in a large commercial installation — and is then distributed to multiple outgoing circuits, each feeding one or more EV chargers.

Without a distribution board, every charger circuit would need its own supply run all the way back to the main incoming switchgear. That’s expensive in cable, time, and complexity. With a TPN board positioned close to the chargers, you run one large supply to the board and distribute from there — much more practical and cost-effective at scale.

The TPN board also provides a single point of isolation for the entire EV charging installation — one switch to make the whole area dead for maintenance. That’s an important safety and operational feature for any managed commercial site.

When Do You Need a TPN Distribution Board?

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5 or more EV charger circuits

Below 5 chargers, multi-charger WCED boards are generally the most cost-effective solution. Above 5, a TPN distribution board with individual circuit RCBOs becomes more practical and economical.

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Long cable runs to chargers

Where chargers are located far from the main incoming supply, a TPN board positioned near the charging area reduces total cable length significantly — one large supply cable to the board, short tails to each charger.

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Phased installation plans

Where the site will grow — installing 6 chargers now with plans for 12 later — a correctly sized TPN board with spare ways accommodates expansion without rewiring the distribution.

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Managed commercial sites

Car parks, hotel sites, fleet depots, and business parks where a single point of isolation and a clear distribution architecture are requirements of the site operator or property manager.

The EcoHarmony TPN Distribution Board

Commercial 3-phase distribution · 125A · SPD option · £85

TPN Distribution Board — 125A 4-Pole Main Switch + SPD

The standard specification for commercial EV charging distribution. 125A 4-pole main switch for 3-phase + neutral isolation. Multiple outgoing ways for individual circuit RCBOs. Optional 4-pole SPD for surge protection at the distribution point. Sized for sites with 5–20+ charger circuits depending on individual charger draw.

  • 125A 4-pole main isolating switch
  • Three-phase + neutral distribution
  • Multiple outgoing RCBO ways
  • 4-pole SPD option for surge protection
  • Suitable for 22kW charger circuits (32A per phase)
  • Commercial grade — designed for managed site installation
Buy — £85.00 →

How the Distribution Architecture Works

A well-designed commercial EV charging distribution typically follows this structure:

1

Main incoming supply

3-phase supply from the DNO (Distribution Network Operator) or landlord’s supply. On a PME supply, PEN fault detection is installed at or near the main incoming point — before the TPN distribution board.

2

TPN distribution board

Mounted close to the charging area. 125A 4-pole main switch provides a single isolation point for the entire EV charging installation. SPD at this point protects all downstream circuits. Individual outgoing ways for each charger circuit RCBO.

3

Individual circuit RCBOs

Each charger circuit (or pair of chargers if load-sharing) gets its own RCBO in the TPN board. 40A for 22kW chargers, 20–32A for lower-rated chargers. This provides the per-circuit residual current and overcurrent protection required by BS 7671.

4

EV chargers

Each charger fed directly from its RCBO. Cable sizing from the RCBO to the charger based on circuit length and installation method. Trunking or armoured cable for surface runs in car parks and outdoor areas.

PME protection placement on commercial sites

On a PME supply, PEN fault detection must be upstream of the EV charger circuits. On commercial sites, this is typically installed at the main incoming point or in a dedicated PME board upstream of the TPN distribution. The TPN board itself does not contain PME protection — that’s provided separately upstream. EcoHarmony can advise on the correct architecture for your specific site.

Sizing a TPN Distribution Board for EV Charging

Site scale Total charger capacity Main switch rating Cable to board (approx)
5–6 chargers at 22kW Up to 132kW 125A 4-pole 70mm² 4-core SWA (depending on diversity)
8–10 chargers at 11kW Up to 110kW 125A 4-pole 70mm² 4-core SWA (depending on diversity)
10+ chargers with smart load management Subject to diversity 125A+ 4-pole Designed to actual peak draw with load management

Diversity is critical on commercial EV charging sites. A site with 10 × 22kW chargers does not draw 220kW simultaneously in most real-world scenarios — not all bays are occupied at peak times, and vehicles reach their onboard charge limit before the session ends. Proper diversity assessment significantly reduces supply and cable requirements. EcoHarmony can assist with diversity calculations for commercial specifications.

Commercial Site Types — Typical Specifications

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Workplace charging (10–30 bays)

Typically 7kW or 11kW chargers for overnight or all-day dwell. Often split across multiple TPN sub-boards by zone. Smart load management usually specified to stay within supply limits during working hours.

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Hotel & hospitality (4–20 bays)

Often 7kW for overnight stays, sometimes 22kW for day visitors. MID metering frequently specified for billing. A single TPN board typically covers the full installation unless the site is very large.

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Car parks (20–100+ bays)

Multi-zone distribution with TPN boards per zone, connected to a main incoming panel. 22kW common for visitor charging. OCPP management system integration required for billing and access control.

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Fleet depots

Overnight charging focus — high diversity, multiple vehicles drawing overnight means lower peak demand than rated capacity. Smart scheduling often eliminates the need for supply upgrades at existing sites.

Frequently Asked Questions

What is the difference between a TPN board and a standard consumer unit?
A standard domestic consumer unit is typically single-phase (or split-phase in some older installs) and rated for household loads. A TPN (Three-Pole and Neutral) distribution board is designed for three-phase commercial and industrial distribution, with a 4-pole main switch that isolates all three phases and neutral simultaneously. They are different products for different applications.
Does the TPN board include PME protection?
No. The TPN distribution board provides distribution, isolation (main switch), and with the SPD option, surge protection. PME/PEN fault detection must be provided separately, upstream of the TPN board, as a dedicated device. EcoHarmony can advise on the correct upstream PME protection for your site.
How many charger circuits can the 125A TPN board support?
At 32A per circuit (22kW charger), a 125A supply could theoretically support approximately 3–4 simultaneous full-power chargers. In practice, with diversity and smart load management, a 125A supply can comfortably serve 8–15 charger circuits depending on usage patterns. The board itself has multiple outgoing ways for individual circuit RCBOs.
What cable do I need from the main supply to the TPN board?
For a 125A 3-phase supply, typically 70mm² 4-core steel wire armoured (SWA) cable, subject to cable length, installation method, and actual load calculations. This must be determined by the installing electrician based on the specific site conditions and confirmed load assessment.
Do I need an SPD at the TPN board if there’s already an SPD at the main incoming?
Depending on the cable length between the main incoming SPD and the TPN board, a second SPD at the TPN board may be required. BS 7671 Appendix 16 and IEC 62305 guidance indicates that a second SPD is generally required where the cable between SPDs exceeds approximately 10–30 metres. An electrician should assess this as part of the overall lightning and surge protection design.
Can the TPN board be expanded if the site grows?
Yes — provided spare ways are available in the board for additional RCBOs. This is why EcoHarmony recommends sizing the TPN board with spare capacity at initial installation rather than fitting the minimum number of ways. Adding ways to a full board usually requires a new board; adding RCBOs to a board with spare ways is a simple extension.
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EcoHarmony — commercial EV charging infrastructure supply

We supply the full commercial EV charging distribution stack — TPN boards, 3-phase PME protection, 3-phase RCBOs, SPDs, kWh meters, and enclosures. Volume pricing for commercial programmes and OEM supply. Technical support on site architecture and product selection.

  • 🧠 Technical support on commercial site design and product selection
  • 💷 Volume pricing — framework pricing for large programmes
  • 📦 OEM supply for commercial charging infrastructure projects
  • 🚚 Same-day dispatch on stock lines

Specifying a commercial EV charging installation?

Tell us the number of bays, charger power rating, and supply type — we’ll confirm the distribution architecture and product list.

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Technical Glossary

TPN
Three-Pole and Neutral — distribution board or switching arrangement with three-phase live conductors plus neutral. Standard format for commercial 3-phase power distribution.
4-pole main switch
Isolating switch that disconnects all three phase conductors and the neutral simultaneously. Required for safe isolation of 3-phase installations. The EcoHarmony TPN board includes a 125A 4-pole main switch.
Diversity
The ratio of expected simultaneous peak demand to total installed capacity. A site with 10 × 22kW chargers rarely draws 220kW simultaneously — diversity assessment determines actual expected peak demand for supply and cable sizing.
Sub-mains
Distribution cable from the main incoming switchgear to a sub-distribution board (the TPN board in this context). Sub-mains sizing is based on the rated capacity of the sub-board’s main switch.
SWA
Steel Wire Armoured cable — mechanically protected cable used for underground runs and surface-mounted commercial installations. Standard for sub-mains and longer EV charger circuit runs in commercial settings.
OCPP
Open Charge Point Protocol — communication standard for connecting chargers to management platforms. Required for billing, access control, and energy management on commercial sites.
MID metering
Measuring Instruments Directive — legally accurate energy metering for billing purposes. Required where charging costs are passed to users (e.g. pay-per-use car parks, fleet cost allocation).
TPN 3-phase distribution boards Commercial EV charging · 125A · EcoHarmony UK
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