TPN 3-Phase Distribution Boards Explained

TPN (Triple Pole and Neutral) distribution boards are designed for 3-phase supplies. They distribute load across three phases, accept 3-pole and single-pole MCBs or RCBOs, and are the correct board type for 11–22kW EV charging, commercial premises, and any installation supplied from a 3-phase incomer.

As 3-phase EV charging becomes more common in commercial and residential settings, and as solar and battery systems increasingly use 3-phase supplies, TPN distribution boards have moved from a specialist commercial product to something many domestic and commercial installers encounter regularly. This guide explains what TPN means, how these boards differ from single-phase consumer units, and when one is required.

What TPN means

TPN stands for Triple Pole and Neutral — meaning the board's busbar carries all three phases (L1, L2, L3) and a neutral conductor. This allows both 3-pole devices (connecting to all three phases simultaneously, for 3-phase loads) and single-pole devices (connecting to one phase and neutral, for single-phase loads) to be installed in the same board.

This flexibility is one of the key advantages of a TPN board in a mixed installation — you can feed a 22kW 3-phase EV charger from a 3-pole MCB alongside single-phase lighting and socket circuits on individual RCBOs, all from the same board.

TPN board vs single-phase consumer unit

Feature	Single-phase consumer unit	TPN 3-phase board
Supply voltage	230V (L + N)	400V 3-phase (L1 + L2 + L3 + N)
Busbar phases	1	3 (balanced across ways)
3-pole device support	❌	✅
Single-pole device support	✅	✅
Max load per way	Limited to single phase	Can distribute across all 3 phases
Typical applications	Domestic, small commercial	3-phase EV charging, commercial premises, light industrial

WCED WTPN series

The WCED WTPN series provides fully assembled TPN 3-phase distribution boards in 12-way and 18-way configurations. Boards are supplied complete with a 4-pole 100A main isolator, 4-pole Type B 40A RCD, neutral bar, earth bar, and SPD — ready to connect on site without field assembly. Available in metal (IP40) for indoor use and configured for standard commercial and EV charging applications.

4-pole 100A main isolator included

4-pole Type B RCD for 3-phase EV protection

SPD built in — Type 2 40kA

12-way and 18-way options

Accepts 3-pole and single-pole devices

Metal IP40 construction

Sizing a TPN board for EV charging

Charger type	Charger output	Current per phase	Board/OCPD required
Single-phase 7kW	7kW (32A)	32A on 1 phase	Single-phase board, 32A RCBO
3-phase 11kW	11kW (16A/phase)	16A × 3 phases	TPN board, 3-pole 20A MCB + 4-pole Type B RCD
3-phase 22kW	22kW (32A/phase)	32A × 3 phases	TPN board, 3-pole 40A MCB + 4-pole Type B RCD

Shop WCED TPN 3-Phase Distribution Boards

Fully assembled TPN boards with main isolator, 4-pole Type B RCD, SPD, and busbar ready to install. In stock.

View TPN boards →

Frequently Asked Questions

Can I install a TPN board on a single-phase supply?

No — a TPN board requires a 3-phase supply. On a single-phase supply, two of the three busbars would be dead, and any 3-pole devices would not function correctly. If you have a single-phase supply and need an EV charging sub-board, use a single-phase consumer unit or EV connection unit instead.

How do I balance the load across three phases?

When populating a TPN board with single-phase circuits, distribute them as evenly as possible across all three phases — roughly equal numbers of circuits on L1, L2, and L3. This minimises neutral current and prevents one phase from being overloaded while others are lightly loaded. Most TPN board manufacturers label the ways by phase to make this straightforward.

Do I need a 3-phase supply from my DNO for a 22kW EV charger?

Yes — a 22kW charger requires a 3-phase supply. This typically requires a new supply application to your DNO (UK Power Networks, Western Power Distribution, etc.). The DNO will assess whether your existing supply infrastructure can support the additional load and provide a quotation for the new connection. Lead times vary but are typically 4–12 weeks.

Further reading:
4-pole vs 2-pole RCDs for 3-phase
What is a Type B RCD?
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