Decoding a device line
Each line is written so that any manufacturer's catalogue can answer it. A line such as RCBO, B16, 30 mA type A, 2 mod. breaks down like this:
- The device kind — MCB, RCD, RCBO, AFDD, SPD, voltage relay, main breaker or distribution block.
- The curve letter and rating — B16 means trip curve B at 16 A, see MCB ratings and curves.
- The sensitivity and type — 30 mA type A, with an added (S) when the device must be selective; see RCD types.
- The width in modules — how much DIN rail the device occupies.
A module is the standard 17.5 mm width of a single-pole DIN-rail device. A plain MCB is 1 module, an RCBO or RCD usually 2, a three-phase incomer 4. The enclosure is sold by module count per row, so those widths are what decides which enclosure fits — see choosing the panel enclosure.
Cable lines read like Cable 3x2.5 mm² copper: three cores (L, N, PE) at that cross-section, with the number of runs given but not the metres — length is measured on site by the installer. Panel wire is listed separately by cross-section as a rough estimate with reserve. Accessory lines cover N and PE busbars, the incoming distribution block and comb busbars, each with its terminal count or length in modules.
What must never be downgraded
- RCD type. A type B replaced by a type A leaves the circuit unprotected and blinds the panel.
- AFDD. Dropping it removes the only protection against hidden arcs, see what is an AFDD.
- Cable cross-section. Thinner cable with the same breaker is the classic fire cause, see cable cross-sections.
- Enclosure material and rating. Metal and IP ratings are chosen for a reason, not for looks.
Rating and curve may only be changed together with the cable, never on their own.
Buy from a reputable seller
Counterfeit modular breakers are common and genuinely dangerous: undersized contacts, missing arc chutes, RCDs whose test button works while the sensing core does not. They look identical and cost noticeably less. Buy from an electrical wholesaler or an authorised dealer, and be suspicious of unusually cheap lots.
What the list does not include
- Wire ferrules in the sizes matching your panel wire.
- Comb busbar end caps and insulating covers for cut combs.
- Labels or a label printer for circuit marking.
- Cable ties, ties bases and a small length of DIN rail spare.
- Cable glands or grommets where cables enter the enclosure.