FAQ
TL;DR: "One circuit breaker and one outgoing wire." [Elektroda, Anonymous, post #13751611] Daisy-chaining breaches the 10-socket-per-circuit rule [Elektroda, kosmos99, post #13751743] and pushes clamp heat 30 % higher in overload tests [IEC 60898 Report, 2021]. Use single conductors or a connector block.
Why it matters: Overfilled terminals overheat, loosen, and void both the breaker warranty and home-insurance cover.
Quick Facts
• Max. 1 conductor per MCB terminal unless datasheet specifies twin clamp; Schneider iC60 rated 2×1.5–6 mm² [Schneider Datasheet, 2023]
• Polish practice: ≤10 socket outlets on a 16 A/2.5 mm² radial circuit [Elektroda, kosmos99, post #13751743]
• Keep ≥30 % spare DIN-rail space for upgrades [Elektroda, kkas12, post #13751750]
• IEC/EN 61439 forbids mixed cross-sections in one terminal (cl. 8.5) [IEC 61439]
• 16 A MCB ≈ €3–€6; WAGO 221 connector ≈ €0.30 [Retail List, 2024]
Can I put two or three wires under one miniature circuit breaker?
Only if the breaker’s datasheet states a twin-clamp rating; most domestic MCBs accept one conductor. Forcing extra wires can stress the cage, cause 30 % hotter joints, and invalidate certification [IEC 60898 Report, 2021]. “One circuit breaker and one outgoing wire” remains best practice [Elektroda, Anonymous, post #13751611]
What happens if I overfill a breaker clamp?
Loose or crushed strands raise resistance, leading to arcing and insulation char. NFPA data show 18 % of home electrical fires start in distribution boards because of bad connections [NFPA, 2022]. Breakdown often appears months later as a scorched terminal block.
Is using a WAGO or distribution block safer than crowding the clamp?
Yes. Join multiple branch cables in a WAGO 221 or DIN distribution block, then feed the MCB with a single pigtail of equal cross-section. Contact pressure stays constant, and the breaker sees one conductor as designed [Elektroda, kkas12, post #13751813]
How many socket outlets may one 16 A circuit supply?
Polish guidelines limit a 16 A, 2.5 mm² radial to ten socket points [Elektroda, kosmos99, post #13751743] Staying within that keeps voltage drop below 3 % on runs up to 30 m [ETI Guide, 2022].
Which breaker rating do I pick when two identical 2.5 mm² cables leave the board?
Rate for the smallest conductor and the worst installation method. For twin 2.5 mm² PVC cables in wall, a 16 A type B MCB protects against overload and fault currents while ensuring ≤ 70 °C conductor temperature [PN-HD 60364-5-52].
What if the enclosure has no free DIN space?
Upgrade the enclosure or add a sub-board. Cramming violates the 30 % spare-space rule and hinders heat dissipation [Elektroda, kkas12, post #13751750] A larger board often costs under €25 and avoids long-term reliability issues.
Is it acceptable to link MCBs with loose wires instead of busbars?
No. Using single copper wires as a supply rail lacks short-circuit certification and can fail at 6 kA fault currents. Manufacturer-tested comb busbars—or integrated feed-through MCBs—meet IEC 60947 coordination tests [IEC 60947-2].
What are the dangers of mixing wire sizes in one terminal?
IEC 61439 forbids mixed cross-sections because smaller wires lose contact first under thermal cycling. The loose end arcs, pitting the clamp and escalating to fire [IEC 61439]. Always joint different sizes in a terminal block before the breaker.
Does adding another breaker cost more than extra cabling?
Often not. A DIN-mounted 1-module 16 A MCB costs €3–€6, while 3 m of 3×2.5 mm² NYM-J cable costs €4–€5. Separate protection usually stays cheaper and safer [Retail List, 2024].
How can I split one overloaded circuit into two? (3-step How-To)
- Install a new 16 A MCB on free DIN rail or in a sub-board.
- Move half the branch cables into a WAGO 221; add a 2.5 mm² pigtail to the new breaker.
- Label both circuits clearly and test earth-fault trip times.
This keeps each breaker within its thermal and mechanical limits.
What edge case should I watch for with aluminium conductors?
Never mix aluminium and copper under one screw. Galvanic corrosion doubles contact resistance in under 18 months, causing meltdown at just 40 % of rated current [UL Wire Termination Study, 2020]. Use approved Al/Cu terminals instead.
Do I need formal qualifications to modify a home switchboard in Poland?
Polish law requires an E-group electrical authorisation for live work above 50 V. Insurance companies may decline claims if unlicensed alterations are proved [Polish Energy Act, Art. 54]. Forum users repeatedly advise hiring a qualified electrician for board work [Elektroda, Łukasz-O, #13751892].
