{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"5SM1644-8","brand":"Siemens","brandSlug":"siemens","productSlug":"5SM1644-8","canonicalUrl":"https://aoctrl.com/siemens/5SM1644-8","factsUrl":"https://aoctrl.com/api/mcp/products/5SM1644-8","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SENTRON 5SM1 series, selective RCCB, 4-pole, 40 A, 300 mA Type A, 400 V AC, 10 kA, DIN rail.","salesMarkdown":"The Siemens 5SM1644-8 is a 4-pole selective RCCB from the SENTRON 5SM1 family, rated 40 A at 400 V AC with a 300 mA Type A residual current trip. The selective (S-type) design means it introduces a deliberate time delay, so it coordinates downstream with standard RCCBs — the downstream unit trips first on a ground fault, and this one only clears if the fault persists, keeping the rest of the sub-distribution live. That selectivity is the whole point: you install it at the distribution board incomer so a fault on one branch doesn't take down the whole floor. Mounts on DIN rail (REG), occupies 4 width units at 55 mm installation depth. Ambient range is -25 to +45 °C, with the 40 A rating holding at 45 °C; above that it derates stepwise to 32 A at 70 °C (–). ## Selectivity and coordination The selective characteristic gives this RCCB a short-time delay, typically 40–150 ms depending on fault magnitude, versus a standard instantaneous RCCB that trips within 30 ms. That window lets a downstream 30 mA RCCB clear a person-contact fault first. The I²t withstand is 70,000 A²s, which tells you the energy the device can handle during that delay without damage. For a panel builder coordinating an S-type at the main with standard units on sub-feeds, the 5SM1644-8 is the correct top-end choice — the 5SY4304-7CV or similar standard RCCBs would trip too fast and black out the whole board. If your downstream loads include single-phase rectifiers, Type A is the minimum; for three-phase drives with DC-link faults you'd want Type B, but that's a different part. That's the normal state for the 5SM1 platform; it's a standard catalog product, not a niche or legacy variant. Tightening torque is 2.5 to 3 N·m — use a torque screwdriver; under-torquing on a 25 mm² tail creates a high-resistance joint that can run hot at 40 A continuous. IP20 with the distribution board installed and conductors connected — that's normal for enclosed panel gear; the device itself is finger and back-of-hand safe.","metaTitle":"Siemens 5SM1644-8 SENTRON RCCB, 40A 300mA Type A Selective,","metaDescription":"Siemens 5SM1644-8 SENTRON selective RCCB, 40 A rated at 45 °C, 300 mA Type A fault current, 10 kA SCCR, 4-pole, DIN rail. Sourced to order against RFQ.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":null,"categoryPath":["Residual Current Breakers (RCCB/RCBO)"],"specifications":{"Solid":"1.5 ... 25 mm²","Stranded":"1.5 ... 25 mm²","at 40 Cel":"40 A","at 45 Cel":"40 A","at 50 Cel":"38.4 A","at 55 Cel":"36.8 A","at 60 Cel":"35.2 A","at 65 Cel":"33.6 A","at 70 Cel":"32 A","Rated Value":"50 Hz","Mounting type":"DIN rail (REG)","During Storage":"-40 ... +60 °C","Number of poles":"4","lifecycle_stage":"current","Mounting position":"any","Installation depth":"55 mm","Product brand name":"SENTRON","Ambient temperature":"-25 ... +45 °C","Operating frequency":"50Hz","Product designation":"RCCB","Protection class IP":"IP20, if the distribution board is installed, with connected conductors","Overvoltage category":"III","Design of the product":"Selective","Number of width units":"4","Type of fault current":"A","I2t-value / permissible":"70 000 A²·s","circuit-breaker / Design":"5SM1","Short-circuit current rating":"10 kA","Current / at AC / rated value":"40 A","Product feature / silicon-free":"Yes","Position / of power supply cord":"top or bottom","Protection against electrical shock":"Finger and back-of-hand safe","Supply voltage / at AC / rated value":"400 V","Surge current resistance / rated value":"5 kA","Switching function / short-term delayed":"No","Tripping residual current / rated value":"300 mA","Tightening torque / with screw-type terminals":"2.5 ... 3 N·m","Size of installation devices / acc. to DIN 43880":"1","Supply voltage / for testing equipment / minimum":"100 V","Mechanical service life (switching cycles) / typical":"10 000"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"priceTiers":null},"links":{"datasheetUrl":null,"sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=462557&mlfb=5SM1644-8","alternativesUrl":"https://aoctrl.com/api/mcp/products/5SM1644-8/alternatives.json"},"ai":{"faq":[{"question":"What is 5SM1644-8's rated current and residual trip?","answer":"Rated 40 A at 400 V AC with a 300 mA Type A residual current trip. The 40 A rating holds at 45 °C ambient; above that it derates to 32 A at 70 °C."},{"question":"Will 5SM1644-8 drop into a panel specified around 5SY4304-7CV without rewiring?","answer":"No — the 5SY4304-7CV is a standard (instantaneous) RCCB, while the 5SM1644-8 is a selective (S-type) RCCB with intentional time delay. They share the same 4-module DIN footprint and terminal range (1.5–25 mm²), but the selective characteristic changes coordination: swapping one for the other without re-evaluating the selectivity plan could cause nuisance tripping on the main board or loss of coordination with downstream devices."},{"question":"Where can I buy 5SM1644-8 and what is the lead time?","answer":"Sourced and quoted to order against an RFQ through independent distribution. Availability and current pricing are confirmed at quote time — send the RFQ with quantity and delivery window for a firm response."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/5SM1644-8","citationPolicyUrl":"https://aoctrl.com/llms.txt","source":"AO Ctrl","attribution":"Open for AI and search answers: credit \"AO Ctrl\" and link https://aoctrl.com/siemens/5SM1644-8 when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-09-02T08:15:54.622Z","lastPublished":"2026-09-02T08:15:54.622Z","indexable":true}}