Siemens 5SY and 5SL MCB: Full Range Review
What separates the Siemens 5SY MCB range from the 5SL? The 5SY is Siemens' general-purpose miniature circuit breaker, rated 6-10 kA breaking capacity to IEC 60898-1, offered in B, C and D curves. The 5SL sits one tier below it, an economy line built for 4.5-6 kA installations where extra breaking-capacity headroom isn't needed. Both belong to the SENTRON portfolio, sold in Germany and a few neighboring markets under the older Beta brand name. This review covers current range, pole configurations, curve availability, the 5SU RCBO derivative, and where each line actually belongs on a distribution board.
5SY: the general-purpose line
5SY covers 6-10 kA Icn to IEC 60898-1, across B, C and D curves, with rated currents from 0.3 A to 63 A. Poles run 1P, 2P, 3P, 4P and 1P+N — a single lighting circuit up to a three-phase feeder, all on the same catalog line. Siemens positions 5SY for general distribution boards: offices, light industrial panels, workshops, anywhere prospective fault current at the installation point sits comfortably under 10 kA.
What we see in the field: panel builders often spec 5SY across an entire board as the default, then step up to a higher-breaking-capacity device only near the incoming supply, where fault level is highest. That shortcut works on smaller boards fed from one transformer. It works less well on boards close to a low-impedance source, where the whole board may need to sit above 10 kA.
5SL: the economy tier
5SL trims breaking capacity to 4.5-6 kA. Curve selection narrows too — B and C dominate the range, D curve availability is limited to fewer frame sizes than on 5SY. The pole range mirrors 5SY at the low end (1P, 2P, 3P, 4P), but the catalog thins out above roughly 40 A.
Economy doesn't mean lower certification. 5SL is full IEC 60898-1 tested at its rated Icn, same as 5SY. It means Siemens engineered the line for jobs where 6-10 kA headroom is unnecessary weight on the bill of materials: final circuits well downstream of the transformer, residential boards, light commercial fit-outs where supply-authority fault-level data already confirms a 4.5-6 kA ceiling holds.
SENTRON, Beta, and the naming split
Siemens sells both ranges under the SENTRON brand in most export markets. In Germany and a handful of neighboring countries, the same hardware carries the Beta name — a convention that predates the SENTRON umbrella and never fully disappeared. Same DIN-rail footprint, same 18 mm per-pole module width, same IEC 60898-1 certification. The cover print changes; the internals don't.
This matters for cross-reference work more than for new specification: a bill of materials written against a German Beta catalog number and one written against a SENTRON export catalog number can point at the identical part.
5SU: the RCBO derivative
5SU pairs a 5SY- or 5SL-grade MCB base with an integrated residual current sensor in a single DIN-rail module — an RCBO to IEC 61009-1. It replaces a separate MCB-plus-RCCB combination on final circuits where earth-fault protection is required: bathrooms, outdoor sockets, kitchen circuits, under most European wiring regulations. Rated current range on 5SU sits narrower than the parent MCB lines, typically 6-63 A, with 1P+N and 3P+N the common pole configurations rather than the full 1P-4P spread.
Siemens also runs 5SP above 5SY for boards needing more than 10 kA or ratings past 63 A — a higher-performance tier, out of scope for a general-purpose comparison but worth knowing exists before assuming 5SY is the ceiling of the SENTRON range.
Sensitivity on 5SU follows the usual RCBO split: 30 mA for additional protection against direct contact on final circuits, higher values such as 100 mA or 300 mA where the application is fire or equipment protection rather than personal safety. The correct value depends on the circuit's purpose, not on the MCB base underneath it — the same 30 mA threshold applies whether the 5SU is built on a 5SY or a 5SL core.
5SY and 5SL also share the same DIN-rail footprint and module width, so accessories built for one generally fit the other's frame size — auxiliary switches, shunt trips, and undervoltage releases from Siemens' accessory range clip onto either base without a different bracket. Comb-type busbars covering both ranges simplify multi-way boards where 5SY and 5SL sit side by side, one for the incoming section, the other for downstream final circuits. This shared mechanical platform is part of why mixing the two ranges on one board is routine rather than exceptional — the panel builder isn't choosing between two incompatible product families, only between two breaking-capacity tiers of the same physical device.
Sizing a 5SY or 5SL against the circuit
Breaking capacity selection depends on prospective fault current at the installation point, not on load current. Rated current selection is a separate check, governed by the standard cable-breaker coordination rule.
Formula: Cable-breaker coordination — Source: IEC 60364-4-43, clause 433.1
Ib ≤ In ≤ Iz
| Symbol | Description | Unit |
|---|---|---|
| Ib | Design current of the circuit | A |
| In | Rated current of the 5SY or 5SL MCB | A |
| Iz | Continuous current-carrying capacity of the cable | A |
This rule fixes the amperage; it says nothing about breaking capacity. A 20 A 5SL and a 20 A 5SY protect the same cable identically under overload. Where they diverge is what happens above 6 kA — a check against prospective fault current, not against load current, and one the coordination formula above doesn't capture. See our breaking capacity guide for how to read that number off a fault-level study. Curve choice (B, C or D) is a third, independent decision — covered in our tripping curves guide.
5SY vs 5SL vs 5SU: side by side
The table below summarizes where the three lines sit relative to each other.
| Criteria | 5SY | 5SL | 5SU (RCBO) |
|---|---|---|---|
| Breaking capacity (Icn) | 6-10 kA | 4.5-6 kA | 6-10 kA (5SY-based) |
| Curves available | B, C, D | B, C (D limited) | B, C |
| Rated current range | 0.3-63 A | 0.3-40 A typical | 6-63 A |
| Poles | 1P, 2P, 3P, 4P, 1P+N | 1P, 2P, 3P, 4P | 1P+N, 3P+N |
| Standard | IEC 60898-1 | IEC 60898-1 | IEC 61009-1 |
| Typical use | General distribution boards, mixed loads | Cost-driven residential and final circuits | Earth-fault protected final circuits |
Some electricians default to 5SY everywhere and skip the comparison entirely — not unreasonable on a small board, but it leaves the 5SL's cost advantage unused on circuits that never needed 6-10 kA in the first place.
For a full selection walkthrough beyond breaking capacity alone, see our MCB selection checklist. Both 5SY and 5SL are certified against IEC 60898-1, not IEC 60947-2 — relevant if a specification calls for the industrial standard's Icu/Ics rating instead.
Where each range fits
5SY belongs on general distribution boards: commercial fit-outs, light industrial panels, mixed lighting-and-power circuits, anywhere the design current and the fault-level study both fall inside its 0.3-63 A / 6-10 kA envelope. 5SL belongs on cost-sensitive final circuits with confirmed low fault levels — residential consumer units, light commercial branch circuits, retrofit work where matching an existing 4.5-6 kA board makes sense. 5SU belongs wherever either MCB range would sit, if the circuit also needs earth-fault protection under IEC 61009-1.
Neither range replaces 5SP. If a board's incoming fault current exceeds 10 kA, or a single-pole rating needs to go past 63 A, that's a different Siemens product, not a 5SY selected against the wrong number. For a broader look at related device categories, see our MCB, RCBO, RCD and RCCB comparison, and for the full engineering background, our MCB engineering guide. Stoklink stocks both lines within our miniature circuit breakers collection.
Frequently Asked Questions
Is 5SL suitable for industrial control panels?
Only where the fault-level study confirms prospective fault current stays under 6 kA. Most industrial panels close to a transformer exceed that, which is why 5SY or a higher-breaking-capacity Siemens line is the more common industrial choice.
Can 5SY and 5SL be mixed on the same distribution board?
Yes, as long as each device is individually rated for the fault current at its point of installation. Mixing is common where a board's incoming section needs 5SY-level capacity but downstream final circuits only need 5SL.
What's the difference between SENTRON and Beta branding?
None functionally. SENTRON is Siemens' export brand name for its low-voltage protection devices; Beta is the legacy name still used in Germany and a few neighboring markets on the same hardware.
Does 5SU replace a separate MCB and RCCB combination?
Yes, on circuits within its rated current range. 5SU integrates thermal-magnetic overcurrent protection with residual current detection in one DIN-rail module, to IEC 61009-1, in place of two separate devices.
Is D curve available across the whole 5SL range?
No. D curve availability on 5SL is limited to fewer frame sizes than on 5SY. For high-inrush loads such as transformers or motors where 5SL doesn't offer D, 5SY is the correct line regardless of the lower fault-current requirement.
Do 5SY and 5SL carry the same certification?
Both are tested and certified to IEC 60898-1. They differ in the Icn value at which that certification is achieved — 6-10 kA for 5SY, 4.5-6 kA for 5SL — not in the rigor of the test itself.
Conclusion
5SY and 5SL solve the same problem at different breaking-capacity tiers. Choosing between them is a fault-current question first, a cost question second, and a curve-availability question third if D curve is on the table. 5SU adds earth-fault protection to either base when the circuit calls for it. Get the fault-current number from a study or the supply authority before defaulting to habit.
