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TP&N Distribution Boards Explained: Types, Components and Wiring
Updated October 2026 · Meteor Electrical guides · 9 min read
Quick answer: A TP&N (triple pole and neutral) distribution board takes a three-phase supply, L1, L2 and L3 plus a neutral, and splits it into protected circuits. In the UK and Ireland that supply is nominally 400V between phases and 230V from phase to neutral, so one board can feed three-phase motors and single-phase lighting and sockets. It is used in commercial, industrial and some large domestic installations.
If you are specifying or replacing a board on a three-phase supply, a TP&N distribution board is usually what you need. This guide explains what TP&N means, the difference between Type A and Type B boards, the main components, phase balancing and labelling, where the boards are used and who can install them.
In this guide
What is a TP&N distribution board?
A distribution board receives the incoming supply and divides it into separate final circuits, each with its own protective device. TP&N stands for triple pole and neutral: the board has three line conductors, L1, L2 and L3, and a neutral.
In the UK and Ireland, the nominal voltage between any two phases is 400V and between any phase and neutral it is 230V. That means a TP&N board can supply:
- Three-phase circuits at 400V, using triple-pole devices, for motors, compressors and large heaters.
- Single-phase circuits at 230V, using one phase and the neutral, for lighting, sockets and small equipment.
Phase conductors are identified as brown (L1), black (L2) and grey (L3), with blue for neutral and green and yellow for protective conductors. Older installations may use red, yellow and blue for the phases and black for neutral, so take care when working on mixed colour codes.
How is a TP&N board different from a consumer unit?
A consumer unit is a type of distribution board for single-phase domestic supplies. It is fed by one line and a neutral at 230V and usually built to BS EN 61439-3, with the extra non-combustible enclosure requirements for dwellings in BS 7671.
A TP&N board does the same job on a three-phase supply. It has a 4-pole incomer and a busbar that carries each phase to the outgoing ways, so it handles higher loads and can supply 400V equipment. In larger buildings, a TP&N board often feeds several sub-distribution boards around the site.
What is the difference between Type A and Type B distribution boards?
The terms Type A and Type B describe how a three-phase board is built and what devices it will accept. The exact definitions vary slightly between manufacturers, so always check the data sheet, but the general difference is:
| Feature | Type A board | Type B board |
|---|---|---|
| Outgoing devices | Single-pole (and sometimes double-pole) MCBs and RCBOs | Single-, double- and triple-pole MCBs, RCBOs and RCDs |
| Three-phase outgoing circuits | Limited or not possible | Yes, with TP devices across L1, L2 and L3 |
| Incoming device | Usually fixed (main switch) | Usually a choice, such as a switch disconnector, MCCB or RCD |
| Typical size | Smaller boards, fewer ways | Larger boards, more ways |
| Typical use | Small shops, offices, larger homes with three-phase supply | Commercial, industrial and mixed three-phase installations |
When is a Type A board enough?
A Type A board suits sites where the outgoing circuits are mostly single-phase, such as lighting and sockets in a small office, with the load spread across the three phases.
When do you need a Type B board?
Choose a Type B board where you need three-phase outgoing circuits, such as motors, plant or sub-main feeds, or where you want a specific incoming device. Many Type B boards accept triple-pole devices in each row of ways.
What is inside a TP&N distribution board?
Most TP&N distribution boards share the same basic parts, although the layout differs between makes.
| Component | What it does | Typical choice |
|---|---|---|
| Incomer / main switch | Isolates the whole board, and in some boards gives overcurrent protection | 4-pole switch disconnector or MCCB, often 100A to 125A |
| Busbar | Carries each phase from the incomer to the outgoing ways | Fully shrouded, phase-segregated busbar |
| MCBs | Protect each circuit against overload and short circuit | SP for 230V circuits, TP for 400V three-phase loads |
| RCBOs | Overcurrent plus earth leakage protection on one circuit | 30mA Type A RCBOs for sockets and final circuits |
| RCDs | Earth leakage protection for a group of circuits | Usually 4-pole where they protect three-phase circuits |
| SPD | Limits transient overvoltages from lightning or switching | 4-pole Type 2 SPD near the incomer |
| Neutral and earth bars | Terminate circuit neutrals and protective conductors | Numbered to match the outgoing ways |
Incomers and main switches
The incomer isolates the whole board so it can be worked on safely. It does not limit the current the building uses; that is set by the supply and the protective devices. Boards are commonly supplied with a 100A or 125A 4-pole main switch, and some take an MCCB or RCD as the incomer. A separate TP&N isolator or switch fuse is often fitted ahead of the board or for local isolation of plant.
MCBs and RCBOs
Single-pole three-phase board MCBs protect 230V circuits, while triple-pole MCBs protect 400V three-phase circuits. RCBOs combine overcurrent and 30mA earth leakage protection in one device, so a fault on one circuit only trips that circuit. For more on trip curves and ratings, see our MCB buying guide.
Surge protection devices
A 4-pole Type 2 surge protection device fitted close to the incomer protects the whole board from transient overvoltages. Many three-phase boards now come with an SPD already fitted. Our guide to SPD installation in a consumer unit explains placement and lead length.
How do you balance phases and label a TP&N board?
Phase balancing
Each single-phase circuit takes its load from one phase, so the designer spreads them across L1, L2 and L3 to keep the current in each phase as even as possible. Ways are usually numbered by phase, for example 1L1, 1L2 and 1L3, which makes the balance easy to see.
- Estimate the design current of every circuit, applying diversity where appropriate.
- Allocate single-phase circuits so each phase carries a similar total load.
- Keep large single-phase loads, such as water heaters, on different phases.
- Record the allocation on the circuit chart, and re-check it when circuits are added.
Good balancing reduces neutral current, stops one phase of the incomer running hot and makes the best use of the supply.
Labelling
- A clear circuit chart showing each way, phase, rating and what it supplies.
- Phase identification for L1, L2 and L3 at the terminals.
- A warning label where 400V is present and would not normally be expected.
- The RCD test notice, periodic inspection notice and any mixed colour code warning required by BS 7671.
- A label identifying where the board is fed from.
Safety: Three-phase circuits carry 400V between phases, which is far more dangerous than a single-phase supply. Isolate and prove dead on every phase before working on a board, and lock off the supply.
Where are TP&N distribution boards used?
| Setting | Why a TP&N board is used |
|---|---|
| Offices and shops | Lighting, small power and air conditioning spread across three phases |
| Factories and workshops | Three-phase motors, compressors, machine tools and welders |
| Plant rooms | Pumps, fans, boilers and other building services |
| Farms | Grain dryers, milking equipment and large motors |
| EV charging and heat pumps | Several chargers or large heat pumps on one site |
| Large homes | Where a three-phase supply has been installed for high loads |
Three-phase power suits these sites because it delivers more power over smaller cables than single-phase, and three-phase motors start and run more smoothly.
How do you choose the right TP&N distribution board?
- Way count: count the circuits you need now, then add spare ways for future expansion.
- Type A or Type B: decide whether you need triple-pole outgoing devices.
- Incomer rating: match it to the supply and maximum demand, such as 100A or 125A.
- Protective devices: check the board accepts the MCBs, RCBOs and SPD you plan to use. Use devices the board manufacturer approves, as mixing makes can invalidate the tested assembly.
- Environment: choose a suitable IP rating and enclosure for plant rooms, external or dusty locations.
- Standards: look for BS EN 61439-3 for boards intended to be operated by ordinary persons.
Our three-phase distribution boards range includes Live boards from 4 to 24 ways, each with a 125A main switch incomer and a 4-pole 20kA/40kA surge protection device. For switchgear, isolators and protective devices, also see the GARO range.
Who can install a TP&N distribution board?
Installing, replacing or altering a TP&N board is a job for a qualified, competent electrician with three-phase experience. The work must be designed, installed, tested and certified to BS 7671 in the UK, or I.S. 10101 in Ireland.
- In workplaces, the Electricity at Work Regulations 1989 (or the Northern Ireland equivalent) require safe systems of work and competent people.
- In dwellings in England and Wales, new boards and circuits are usually notifiable under Part P of the Building Regulations.
- In the Republic of Ireland, use a Registered Electrical Contractor.
- The supply connection itself is the network operator’s responsibility.
A typical installation follows safe isolation, mounting the board, terminating the supply, fitting the protective devices, connecting the circuits and full testing, including continuity, insulation resistance, polarity, phase rotation, earth fault loop impedance and RCD tests.
Key takeaways
- TP&N means triple pole and neutral: L1, L2, L3 and N.
- Nominal voltages are 400V phase to phase and 230V phase to neutral.
- Type A boards take single-pole devices; Type B boards also take triple-pole devices and a choice of incomer.
- The main parts are the incomer, busbar, MCBs, RCBOs, RCDs, SPD and neutral and earth bars.
- Balance single-phase circuits across the three phases and label every way clearly.
- Only a qualified electrician should install a TP&N distribution board.
Choosing a TP&N distribution board
A TP&N distribution board is the standard way to distribute a three-phase supply safely in commercial, industrial and large domestic buildings. Decide between Type A and Type B, size the incomer and way count, plan the phase balance and labelling, and have the board installed and certified by a qualified electrician.
Shop TP&N boards and switchgear
Three-phase boards, MCBs, RCBOs, isolators and surge protection for TP&N installations. Trade prices, next working day delivery across NI & ROI on in-stock orders before 5pm.
Shop TP&N boards Shop GARONeed help choosing? Call our team on 028 8675 1515 (048 from ROI), Monday to Friday, 8am–5pm.
FAQs
What does TP&N mean on a distribution board?
TP&N stands for triple pole and neutral. The board is fed by three line conductors, L1, L2 and L3, plus a neutral. In the UK and Ireland the nominal supply is 400V between any two phases and 230V between any phase and neutral, so the board can feed both three-phase and single-phase circuits.
What is the difference between a Type A and a Type B distribution board?
A Type A board accepts single-pole, and sometimes double-pole, protective devices fed from a fixed busbar, and usually has a fixed incomer. A Type B board also accepts triple-pole devices for three-phase circuits and normally offers a choice of incoming device. Type B boards suit larger or mixed commercial loads.
Does a three-phase distribution board need a neutral?
A board feeding only balanced three-phase loads, such as some motors, can work without one. Most buildings also need 230V single-phase circuits for lighting and sockets, which take their return path through the neutral. That is why TP&N boards, with a neutral bar, are standard in commercial and mixed installations.
Can I have a three-phase board in a house?
Yes, if the property has a three-phase supply from the network operator. Larger homes, farms and properties with heat pumps, several EV chargers or big workshops sometimes have one. A three-phase supply has to be requested from the network operator, and the board must be designed and installed by a qualified electrician.
Why is phase balancing important?
Spreading single-phase circuits evenly across L1, L2 and L3 keeps the current in each phase similar. Good balancing reduces current in the neutral, avoids overloading one phase and its incomer, and makes better use of the supply capacity. The designer should check the balance at the design stage and again when circuits are added.
Who can install a TP&N distribution board?
Only a qualified, competent electrician with three-phase experience should install or alter a TP&N board. The work must meet BS 7671, or I.S. 10101 in Ireland, and be tested and certified. Work in dwellings may also be notifiable under Part P in England and Wales, and the Electricity at Work Regulations apply in workplaces.