Solar · For traders
Which RCD type do PV and battery inverters need - Type A or Type B?
Short answer
Use Type B where the inverter or PCE lacks at least simple separation between DC and AC and could feed smooth DC fault current, unless the manufacturer states a Type A is acceptable. A4 reg 570.6.2.2 requires Type B for non-isolated PCE on battery systems. Type AC devices should not protect inverter circuits, and devices must suit bidirectional power flow.
Last checked 24 September 2026 · 2 sources
In more detail
- IET Wiring Matters Jul 2026 cites 570.6.2.2: Type B for non-isolated PCE.
- A3:2024 530.3.201 bidirectional/unidirectional device selection.
- IET position paper: many legacy RCDs are Type AC and unable to handle DC from inverters; many RCBOs not assessed as bidirectional.
- Plug-in spec: device must limit smooth DC residual current to <=5 mA and not impair upstream RCDs.
- Section 712 Type B provision (simple-separation exception) not re-read this session.
The facts, dated
- 01Maximum smooth DC residual current from a plug-in solar device — 5 mA
standard · GB · checked 24 September 2026 · GOV.UK
- 02BS 7671 reg requiring Type B RCD for non-isolated PCE (per IET) — 570.6.2.2
standard · UK · checked 24 September 2026 · IET
Sources
- GOV.UK — assets.publishing.service.gov.uk/media/6a60a03c47af652afa0c89f5/plug-in-solar-fi…
- IET — electrical.theiet.org/wiring-matters/years/2026/110-july-2026/automatic-disconne…
Last checked: 24 September 2026