If you are protecting a three-phase circuit where smooth DC leakage may be present, a standard Type A device is not always enough. In those situations, a 4-pole Type B RCD is often the correct choice because it monitors all three phases plus neutral and can detect AC, pulsating DC and smooth DC residual currents.
At Power & Data UK, 4-pole Type B protection sits within our wider Type B RCDs and Three Phase ranges, including standalone devices, specialist enclosures and protection setups for inverter-driven applications.
Quick Answer: You generally need a 4-pole Type B RCD when the circuit is three-phase with neutral and the connected equipment can produce smooth DC residual current. That commonly includes some EV charging setups, solar inverters, UPS systems, frequency converters and other inverter-driven loads. If the installation is only single-phase, a 2-pole Type B RCD may be the correct fit instead.
| Device | Use It When | Typical Use Case |
|---|---|---|
| 2-Pole Type B RCD | The circuit is single-phase and smooth DC leakage is still a risk | Single EV charger, single-phase inverter equipment, specialist domestic circuits |
| 4-Pole Type B RCD | The circuit is three-phase with neutral and DC-sensitive protection is required | 3-phase EV charging, solar PV arrays, UPS systems, VFDs, industrial inverter loads |
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The Quick Answer
- Choose a 4-pole Type B RCD when the supply is three-phase + neutral and the connected equipment may generate smooth DC leakage current.
- Common triggers include 3-phase EV charging, solar inverter systems, UPS equipment, variable speed drives and other converter-driven loads.
- If the circuit is single-phase, a 2-pole Type B RCD is often the more appropriate fit.
- For broader spec support, browse our full Type B RCD range and Three Phase protection range.
Related reads: What Is a Type B RCD? · Type A vs Type B RCD – What’s the Actual Difference? · What Is a 3-Phase RCD?
What Does “4-Pole” Actually Mean?
A 4-pole RCD is designed to monitor and disconnect all three live phases plus neutral. That makes it the normal choice where the installation is running on a 230/400V three-phase system rather than a standard single-phase supply.
That pole configuration matters because the protective device needs to match the circuit architecture. On a three-phase system, a 2-pole device simply is not the right format. You need protection that covers the full path of the supply, including the neutral where applicable.
So when people ask whether they need a 4-pole Type B RCD, the first question is not the brand of equipment. It is usually: is this a three-phase circuit, and can the load generate DC-sensitive fault conditions?
When Do You Actually Need a 4-Pole Type B RCD?
You are normally looking at a 4-pole Type B RCD when both of the following apply:
- The circuit is three-phase with neutral
- The connected equipment can create smooth DC residual currents or waveform characteristics that a standard Type A device is not designed to handle reliably
That is why 4-pole Type B devices come up so often around more advanced electrical loads. They are not there for the sake of it. They are there because some modern equipment changes the fault-current picture completely.
Installer’s Pick: The WEV463B-030 4 Pole B-Type RCD is a strong fit for three-phase EV, inverter and industrial protection scenarios where 63A, 30mA Type B protection is required.
If you are working on a higher-load three-phase application, the WEV4100B-030 100A 4 Pole B-Type RCD gives you another route where current demand and board design call for it.
Typical Applications for 4-Pole Type B RCDs
The most common scenarios where a 4-pole Type B RCD enters the conversation are the ones where three-phase equipment and DC-sensitive leakage overlap.
- 3-phase EV charging – especially on commercial installs or multi-point charging setups where the charger specification points you toward Type B protection
- Solar PV and inverter systems – where converter-driven equipment can introduce smooth DC residual currents
- UPS systems – particularly where waveform characteristics make a standard Type A device unsuitable
- Variable speed drives and frequency converters – common on industrial and plant applications
- Specialist three-phase enclosures and pre-wired units – where the protection strategy has already been designed around Type B sensitivity
This is also where three-phase protection ties closely into other site requirements. Depending on the install, you may also be pairing the RCD with surge protection, a suitable TPN board, or other kit from our Three Phase Boards & Accessories range.
2-Pole vs 4-Pole Type B RCD: Which One Is the Right Fit?
The easiest way to separate them is this:
- 2-pole Type B RCD = single-phase circuits
- 4-pole Type B RCD = three-phase + neutral circuits
That means a domestic single EV charger, single-phase inverter setup or specialist heat pump circuit will often sit better with a 2 Pole B-Type RCD – WEV240B-030 or 2 Pole B-Type RCD – WEV263B-030.
But if the equipment is genuinely three-phase, or the board layout is built around a three-phase supply, then you are firmly into 4-pole territory. In that situation, using a 2-pole device is not a sensible workaround. It is the wrong protective format for the circuit.
| Question | 2-Pole Type B | 4-Pole Type B |
|---|---|---|
| Supply type | Single-phase | Three-phase + neutral |
| Typical use | Domestic EV, single-phase inverter loads, heat pump circuits | Commercial EV, PV arrays, UPS, drives, industrial loads |
| Main product examples | WEV240B-030 / WEV263B-030 | WEV463B-030 / WEV4100B-030 |
63A vs 100A: Which Current Rating Do You Need?
Once you know you need a 4-pole Type B RCD, the next decision is usually the current rating. That part is driven by the design current of the installation, the board arrangement and the rest of the protection strategy, not by guesswork.
- 63A 4-pole Type B RCD – a common fit for many three-phase protection scenarios
- 100A 4-pole Type B RCD – more relevant where the load profile or board design pushes beyond that lower rating
On Power & Data UK, the main options in this cluster are:
- WEV463B-030 – 63A, 30mA, 4 Pole Type B RCD
- WEV4100B-030 – 100A, 30mA, 4 Pole Type B RCD
- WME06/SP-B10063 – 6 Way Metal Unit with 100A B Type RCD & 63A MCB
If the job is not actually three-phase, stop there and check the single-phase options first. Many buyers jump straight to “bigger” protection when they really just need the right 2-pole Type B RCD or a dedicated pre-wired board from our Heat Pump Boards range.
Common Mistakes to Avoid
- Choosing 4-pole just because it sounds more heavy-duty – if the circuit is single-phase, it is the wrong format.
- Only thinking about current rating – the pole count and waveform sensitivity matter just as much.
- Assuming Type A is always enough – some inverter-driven loads need DC-sensitive protection that Type A may not handle properly.
- Ignoring the rest of the board spec – on three-phase installs, the RCD choice often needs to work alongside SPDs, 3-phase RCD configurations and suitable enclosures.
- Mixing up standalone devices and complete solutions – sometimes a pre-configured unit is the cleaner route than building it from separate parts.
Regulation Reminder: Where equipment can generate smooth DC residual current, the protective device has to be suitable for that fault profile. On EV charging circuits, one recognised route is a Type B RCD at ≤30mA, while another is a Type A or Type F device used with compliant integrated 6mA DC detection in the charging equipment itself.
Products That Fit the Job
- 4-Pole Type B RCDs: WEV463B-030 63A 30mA · WEV4100B-030 100A 30mA
- 2-Pole Type B RCDs: WEV240B-030 40A 30mA · WEV263B-030 63A 30mA
- Heat Pump Type B Options: WHP240-030 · 8 Way Heat Pump Board · 12 Way Heat Pump Board
- Enclosures & Kits: IP65 Weatherproof EV Kit with B-Type RCD · 6 Way Metal Unit with 100A B Type RCD
Browse collections: Type B RCDs · Three Phase · Heat Pump Boards · Surge Protection · Consumer Units
FAQs
Do I need a 4-pole Type B RCD for every three-phase circuit?
No. The circuit being three-phase tells you the likely pole format, but the need for Type B sensitivity depends on the connected equipment and whether smooth DC residual current is a realistic fault condition.
What is a 4-pole Type B RCD mainly used for?
Common applications include 3-phase EV charging, solar inverter systems, UPS equipment, frequency converters and other inverter-driven loads.
Can I use a 2-pole Type B RCD instead?
Only if the circuit is single-phase. For three-phase + neutral systems, a 4-pole device is normally the correct configuration.
What is the difference between a 63A and 100A 4-pole Type B RCD?
The key difference is the rated current. The right choice depends on circuit design, load and the rest of the protection setup. Compare the 63A version and 100A version before ordering.
Are 4-pole Type B RCDs only for EV charging?
No. EV charging is one major use case, but they are also commonly specified for PV, UPS, industrial drives and other converter-based equipment.
Final Word
A 4-pole Type B RCD is the right call when the install is three-phase + neutral and the load can create smooth DC leakage. That is why they show up so often on commercial EV charging, inverter systems, UPS equipment and drive-based plant.
If the circuit is single-phase, look at a 2-pole Type B RCD instead. If it is genuinely three-phase, make sure the protection format, current rating and wider board setup all line up before you order.
👉 Ready to spec? Browse our full Type B RCD range, compare 4-pole 63A and 4-pole 100A options, or explore our wider three-phase protection range.