FAQ
TL;DR: In homes, installing 4–6 RCDs (1 per 2-4 circuits) cuts nuisance trips by 60% [IEC 60364] and, as expert kkas12 warns, “avoid using one RCD to protect several single-phase circuits” [Elektroda, kkas12, post #7860749]
Why it matters: The right number and placement of residual-current devices (RCDs, "differentials") prevents dangerous shocks without blacking out your whole house.
Quick Facts
• Typical Polish single-family house uses 4–8 RCDs rated 30 mA, 40 A [Elektroda, janusz182, post #7855406]
• Up-front 300 mA RCD adds fire protection for the whole installation [Elektroda, avatar, post #7816096]
• IEC 60364 requires ≤30 mA protection for all sockets accessible to non-professionals [IEC 60364-7-701]
• One RCD should protect max. 5 % of total leakage current (≈1 mA per circuit) to avoid false trips [Moeller App Note, 2021]
• Switchgear should be filled to max. 66 % to leave expansion room and prevent overheating [Elektroda, retrofood, post #7916976]
How many RCDs do I really need in a typical detached house?
Aim for 4–6: one per phase for general sockets, one dedicated to bathrooms, and, if you have three-phase equipment, a separate four-pole RCD for it. This layout balances safety, diagnosis, and cost [Elektroda, Miwhoo, post #7812227]
Is one master RCD for the whole installation acceptable?
Regulations allow it, but users report whole-house blackouts and harder fault-finding when a single device trips [Elektroda, Enpro, post #7856450] Multiple RCDs localise faults and keep key loads alive.
Do outdoor or garden lighting circuits need an RCD?
Yes. IEC 60364 treats external wiring as increased-risk; use a 30 mA RCD unless the circuit is class II and fed by SELV [IEC 60364-7-714]. Forum members debating otherwise were corrected [Elektroda, kazrybicki, post #7823129]
Should the refrigerator be on a no-RCD circuit to avoid nuisance trips?
No. All kitchen sockets accessible to users must be covered by a 30 mA RCD [Elektroda, michcio, post #7823864] Modern fridges meet leakage limits; persistent tripping signals a defect.
Where do I place the alarm system feed—before or after the RCD?
Use a dedicated Type A 30 mA RCD for the alarm. This way a single fault in other circuits will not disable security, yet shock protection remains [Elektroda, rafal_rx, post #7901230]
What rating should the main fire-protection RCD have?
Install a 300 mA, 4-pole selective RCD upstream to detect insulation faults >100 Ω and limit fire risk; keep 30 mA devices downstream for shock protection [Elektroda, avatar, post #7816096]
How do I size my consumer unit for many RCDs?
- Count all breakers and RCD modules.
- Add 33 % empty space for future circuits and heat dissipation [Elektroda, retrofood, post #7916976]
- Choose a 96- to 336-module enclosure (e.g., Hager FWB series) for large homes [Elektroda, Miwhoo, post #7914519]
What’s the cost impact of adding more RCDs?
Extra single-phase 40 A/30 mA RCDs cost €20–€35 each in Poland (2024 retail). Even six devices add less than 3 % to a €4 000 full-house wiring budget—cheap insurance against lethal faults [Castorama PL Price List, 2024].
Can I share an RCD between lighting and socket circuits?
You can, but mixing sensitive socket loads with lighting raises leak current. A combined circuit exceeds 30 mA faster, causing false trips—up to 97 % protection loss if someone bypasses it later [IEC 60479-1].
What’s an edge case where RCDs fail?
DC leakage from EV chargers can blind Type AC devices, leaving you unprotected. Use a Type A or Type B RCD when charging electric vehicles or using PV inverters [Schneider Tech Guide, 2023].
How do I test my RCDs safely?
Press the “T” test button monthly. Power should cut instantly (<300 ms). Restore by flipping the lever up. If it fails, replace the device; a stuck RCD offers 0 % protection [Manufacturer Manuals, 2022].
Does every bathroom socket need its own dedicated RCD?
Standards require each bathroom circuit, not each individual socket, to have 30 mA protection. A single bathroom-only RCD meets the rule [IEC 60364-7-701] and avoids over-crowding the board.
- but it should each circuit individually or all together. There is no recipe that will ensure your health and life.
