Inside the HSJB: what BRE’s impact rig thinks of a 3D printed junction box

Every Grade 3 upgrade hits the same ugly moment: the field joints. The panel is graded, the detectors are graded, the keypad is graded — and then there’s a plastic conduit box on a wall carrying the lot, with no tamper protection, quietly failing the whole design. Full re-containment fixes it, at a cost that can sink the job.

The HSJB exists for exactly that moment.

What it is

A tamper-monitored junction box that retrofits over the existing standard conduit box. Two screws adjacent to the box (drill guide in the kit), cables and tamper loop terminated into a removable 12-point terminal block, the HSJB fitted over the top and secured with two security screws. No conduit modification, no rework, no re-containment. An unprotected field joint becomes a tamper-detecting enclosure in about ten minutes.

How it was tested — clause by clause, in plain English

We sent it to BRE Global and asked them to test it against selected clauses of BS EN 50131-3, commensurate with Grade 3, Type B ancillary equipment. The full report is public — P130175, Issue 1 — and here is what each test actually means:

• Tamper protection (clause 8.7.1): you can’t get into it, or take it apart, without tools and effort. Passed.
• Tamper detection — opening (8.7.2.1): open the housing and the tamper circuit breaks before you can reach anything inside. Passed.
• Tamper detection — removal (8.7.2.2): prise the whole unit off the wall and the rear tamper triggers first. Passed.
• 5 joule impact, IK08 method (BS EN 62262): a 1.7 kg hammer swung to deliver five joules — roughly a deliberate blow with a heavy spanner. Where the impact caused damage, the tamper alarm was generated before access to internal elements was possible, which is the outcome the standard requires. Passed.
• IP40 (BS EN 60529): no ingress by tools or wires a millimetre across. Passed.

One thing we deliberately don’t say: “certified”. BRE tested selected clauses relevant to an ancillary enclosure — there is no full product standard for a retrofit junction box — and the report says what was tested and what passed. That’s why we link the whole report rather than waving a logo at you. Read it; it’s what your compliance file wants anyway.

Where installers use it

• Intruder upgrades to Grade 3 — the classic case: legacy containment, new grading requirement, no budget for re-containment.
• CCTV and access control field joints where a monitored junction is specified.
• Anywhere an unmonitored joint would be the weakest point of an otherwise graded system.

Standard version for fixed 20/25mm conduit positions; adjustable version where the geometry is awkward. Both ship with the drill guide, security screws, terminal block, installation sheet and a certificate of conformity.

The bit nobody expects

It’s 3D printed — production additive manufacturing in ASA, to a locked print profile, with batch traceability. If that sentence raises an eyebrow, good: we wrote about exactly that, and the BRE impact rig was less sceptical than the forums. The part in your hand will settle it: free trade samples here.