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

A 4-pole RCD monitors all three phase conductors and neutral simultaneously. A 2-pole RCD monitors only one phase and neutral. For 3-phase supplies and 3-phase connected equipment, a 4-pole device is required to provide protection across all conductors.

The question of 4-pole vs 2-pole comes up constantly on 3-phase EV charging installations, commercial distribution boards, and any installation supplied from a 3-phase incomer. Getting it wrong either leaves conductors unprotected or introduces unnecessary cost and complexity. This guide explains when each is required and why.

What the pole count actually means

Device	Conductors monitored	Conductors disconnected on trip	Supply type
2-pole RCD	L + N	L + N	Single-phase (230V)
4-pole RCD	L1 + L2 + L3 + N	L1 + L2 + L3 + N	Three-phase (400V)

A 2-pole RCD sums the current on one live conductor and the neutral. If the balance is broken by more than 30mA, it trips. A 4-pole RCD does the same but across all three phase conductors and the neutral simultaneously — the vector sum of all four conductors is monitored. Any leakage on any phase causes the device to trip and disconnect all four conductors.

When is a 4-pole RCD required?

Application	Required device	Reason
3-phase EV charger (11–22kW)	4-pole Type B RCD	3-phase supply, smooth DC leakage risk
3-phase distribution board incomer	4-pole RCD or RCCB	All three phases must be monitored and disconnected
3-phase motor or industrial load	4-pole RCD or RCBO	Complete isolation required on fault
TPN distribution board upstream protection	4-pole time delay RCD	Discrimination across 3-phase downstream devices
Single-phase circuit from 3-phase board	2-pole RCBO per circuit	Each circuit is single-phase — 2-pole is correct

3-phase EV charging — the most common application

The most common reason a UK installer encounters 4-pole RCDs is 3-phase EV charging. An 11kW or 22kW Mode 3 charger is connected to all three phases and neutral. The charger's internal power electronics produce smooth DC leakage currents from the 3-phase rectifier circuit. This requires a 4-pole Type B RCD — not a 2-pole, and not a Type A device.

The WCED WEV 4-pole Type B range (WAR4 series) provides 40A and 63A options at 30mA sensitivity, specifically designed for this application. See our full guide on this topic: What is a Type B RCD?

Can I use two 2-pole RCDs instead of one 4-pole?

No — not for 3-phase equipment. Two 2-pole devices cannot collectively provide the same protection as a single 4-pole device on a 3-phase load. A 4-pole RCD measures the vector sum of all four conductors; two separate 2-pole devices measure two pairs independently and cannot detect leakage that flows between phases. For 3-phase connected equipment, a single 4-pole device is always the correct approach.

Shop WCED 4-Pole RCDs

4-pole Type A and Type B RCDs for 3-phase EV charging and distribution. 40A and 63A at 30mA. In stock.

View 4-pole RCD range →

Frequently Asked Questions

Does a 4-pole RCD need a neutral connection on a 3-phase 3-wire system?

In a 3-phase 3-wire system (no neutral conductor), a 3-pole RCD is technically sufficient. However, 4-pole devices are commonly specified even where no neutral exists, as they provide complete isolation and are more versatile if a neutral is added later. Always check the specific system configuration before specifying.

What current rating should a 4-pole RCD be for a 22kW EV charger?

A 22kW 3-phase charger draws approximately 32A per phase. A 40A 4-pole RCD is typically specified, though 63A is used where the circuit protective device is rated at 63A or where load growth is anticipated. The RCD rating should be at least equal to the circuit's design current and the protective device upstream.

Are 4-pole RCBOs available?

Yes. 4-pole RCBOs (combining 4-pole RCD + 3-phase MCB) are available for 3-phase circuit protection. The WCED WFR series provides 4-pole Type A RCBOs in 32A and 40A C curve configurations. These are used on 3-phase circuits where individual circuit protection rather than upstream RCD coverage is required.

Further reading:
What is a Type B RCD? Why EV charging needs it
TPN 3-phase distribution boards explained
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