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4-Pole vs 2-Pole RCDs for 3-Phase Installations

RCDs & RCBOs

4-Pole vs 2-Pole RCDs for 3-Phase

Pole count and RCD type (A, B, F) are two separate decisions. Get the pole count wrong and the device simply won’t fit the circuit; get the type wrong and the protection has a gap you won’t notice until it matters.

Quick answer

A 2-pole device switches live and neutral, for a single-phase circuit. A 4-pole device switches all three phases and neutral, for a three-phase circuit. You cannot protect a three-phase circuit with a 2-pole device.

What the pole count means

2-pole vs 4-pole RCD A 2-pole device switches live and neutral on a single-phase circuit. A 4-pole device switches all three phases and neutral on a three-phase circuit.LN2-poleSingle-phase circuitL1L2L3N4-poleThree-phase circuit
A 2-pole device covers a single-phase circuit (L + N). A 4-pole device covers a three-phase circuit (L1 + L2 + L3 + N).
2-pole 4-pole
Conductors switched Live and neutral L1, L2, L3 and neutral
Supply type Single-phase, 230V Three-phase, 400V
Typical use Domestic circuits, single-phase EV chargers, single-phase consumer units TPN distribution boards, three-phase EV chargers (11kW/22kW), commercial supplies

Why every phase has to be switched together

On a three-phase circuit, a fault or an earth leakage event can affect the balance across any of the three phases. If an RCD only monitored and switched one or two of them, a fault on the unmonitored phase could go undetected, or the circuit could be left partially live after a trip. A 4-pole device disconnects all three phases and the neutral together, so the whole circuit is isolated on a trip and every phase is monitored.

This is a separate question from RCD type. A three-phase EV charger still needs the Type A vs Type B decision covered in What is a Type B RCD?, on top of needing a 4-pole device rather than a 2-pole one.

Where you’ll meet each

Single-phase domestic consumer units and 7kW single-phase EV chargers use 2-pole RCBOs. TPN distribution boards and 11kW/22kW three-phase EV installations need 4-pole devices throughout, both for the main switch and for any RCD or RCBO protecting the charger circuit.

Shop 2-pole and 4-pole RCDs

Type A and Type B, both pole counts, in stock for domestic and three-phase installs.

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Frequently asked questions

Can I use two 2-pole devices instead of one 4-pole device on a three-phase circuit?

No. A three-phase circuit needs a single device that switches all three phases and the neutral together, so that a trip isolates the whole circuit and every phase is monitored for imbalance. Two separate 2-pole devices don’t achieve this.

Does a 4-pole device cost significantly more than a 2-pole one?

Yes, a 4-pole device costs more than a 2-pole one of the same type and rating, reflecting the additional poles and switching mechanism. It is a mandatory requirement for three-phase circuits rather than an optional upgrade.

If my home has a three-phase supply, does everything need 4-pole devices?

The main incomer and any genuinely three-phase loads (such as a 22kW EV charger) need 4-pole protection. Individual single-phase circuits fed from that supply, such as lighting or sockets on one phase, still use standard 2-pole devices.

RCDs & RCBOsRCBO vs MCB vs RCD ExplainedRCDs & RCBOsRCBO Types Explained: A, B, F and AFDDRCDs & RCBOsWhat Is a Type B RCD?RCDs & RCBOsRCD Trip Sensitivity: 30mA vs 100mA vs 300mA

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