Xmas Special | Failed SPDs, Missing Protection & Why the MCB Still Matters

It’s the third Torque Up festive special, but this year the tinsel takes a back seat and the lads go deep on the technical question hitting installs up and down the country:Can a Type 2 SPD rely on an upstream service fuse for overcurrent protection, or must it have a dedicated protective device within the installer’s control?The sparks’ sentiment in the room is clear:manufacturer thermal ratings are part of the product design, but they do not guarantee compliance under BS 7671 if there is no dedicated, testable, local overcurrent protective device protecting the SPD as part of the installation. What you’ll take from this episode:● A thermal disconnection flag is a failsafe, not overcurrent protection● The upstream DNO fuse is not dedicated to the SPD circuit, and has unknown characteristics for selectivity and verification● Install design must meet the literal minimums of BS 7671 installers can verify and test● Why Navitas kept the 32A MCB in their SPD consumer unit design when others removed it● The wider industry frustration: installs previously passed are now being flagged for missing protection● Why electricians care more about predictable disconnection than tidy ratings claimsThis episode is educational trade discussion and reflects installer opinion and public regulatory interpretation conversations only. Nothing stated alleges wrongdoing by any person, brand, or organisation, nor constitutes legal or professional instruction. Always consult BS 7671:2018+A2:2022 and the Building Regulations when determining compliant protective device requirements.Season long sponsor: Chauvin Arnoux00:00 Xmas Special Intro02:45 The SPD failure story08:30 Thermal disconnector vs overcurrent protection14:10 The upstream fuse problem explained20:20 Manufacturer claims vs installer verification27:40 Why inspectors flag missing OCPD35:15 Navitas testing and product design decisions41:55 Installer community frustrations48:30 Who carries the risk when interpretation shifts53:20 What installers should actually verify59:10 Big industry question posed back to sparks1:03:45 Xmas chaos interlude1:05:44 CSPs and clearer communication chat1:12:31 Worst Xmas crackers and gifts1:14:34 Compliance psychology returns1:18:46 Signing off for the year, looking ahead