Q: What type of RCD do I need?

Type AC suits general socket and lighting circuits. Type A is the minimum for circuits with electronics that produce pulsating DC fault currents — EV chargers, most modern appliances and solar PV (AC side). Type B is needed where smooth DC fault currents are possible, such as VFDs/inverters and some EV and PV equipment.

Q: What RCD sensitivity should I use?

30 mA is required for additional (personal) protection on socket circuits, bathrooms, outdoor circuits and similar (BS 7671 Reg 411.3.3). 100 mA or 300 mA is used for fire protection or as a time-delayed (S-type) upstream device for discrimination, not for personal protection.

Q: What is the difference between a Type A and Type B RCD?

A Type A RCD detects sinusoidal AC and pulsating DC residual currents. A Type B RCD additionally detects smooth (pure) DC residual currents, which electronic drives, some EV chargers and PV inverters can produce. Type B is more expensive, so it is only specified where the equipment requires it.

Q: Do EV chargers need a special RCD?

Yes — an EV charging point needs 30 mA RCD protection plus protection against smooth DC fault current. That means either a Type B RCD, or a Type A RCD combined with 6 mA DC fault detection (often built into the charger). Always follow the charger manufacturer's instructions and the IET Code of Practice.

Question 1

What type of RCD do I need?

Accepted Answer

Type AC suits general socket and lighting circuits. Type A is the minimum for circuits with electronics that produce pulsating DC fault currents — EV chargers, most modern appliances and solar PV (AC side). Type B is needed where smooth DC fault currents are possible, such as VFDs/inverters and some EV and PV equipment.

Question 2

What RCD sensitivity should I use?

Accepted Answer

30 mA is required for additional (personal) protection on socket circuits, bathrooms, outdoor circuits and similar (BS 7671 Reg 411.3.3). 100 mA or 300 mA is used for fire protection or as a time-delayed (S-type) upstream device for discrimination, not for personal protection.

Question 3

What is the difference between a Type A and Type B RCD?

Accepted Answer

A Type A RCD detects sinusoidal AC and pulsating DC residual currents. A Type B RCD additionally detects smooth (pure) DC residual currents, which electronic drives, some EV chargers and PV inverters can produce. Type B is more expensive, so it is only specified where the equipment requires it.

Question 4

Do EV chargers need a special RCD?

Accepted Answer

Yes — an EV charging point needs 30 mA RCD protection plus protection against smooth DC fault current. That means either a Type B RCD, or a Type A RCD combined with 6 mA DC fault detection (often built into the charger). Always follow the charger manufacturer's instructions and the IET Code of Practice.

RCD Selector

RCD Selector

Choosing the right RCD

Frequently Asked Questions

What type of RCD do I need?

What RCD sensitivity should I use?

What is the difference between a Type A and Type B RCD?

Do EV chargers need a special RCD?

Free: BS 7671 Quick Reference Card