The definition of galvanised electrical conduit (thin-wall galvanised steel conduit for electrical raceways), the thin-wall / thick-wall thickness boundary, the minimum wall thickness in dry indoor locations, and the ban on fusion welding of steel conduit (GB 50303-2015, GB 55024-2022, DB11/T 1832.17-2021)

Topic Positioning

What galvanised electrical conduit (habitually "electrical conduit" in the electrical raceway trade) is - the thin-wall galvanised steel conduit protecting insulated conductors / cables in electrical works - plus the code basis for its wall-thickness boundary, material class, jointing process and laying requirements. It separates "galvanised electrical conduit" from easily confused names such as "galvanised steel pipe (SC)" and "set-screw thin-wall steel conduit (JDG / KBG)".

Core Conclusions

1. Material essence and the thin-wall / thick-wall boundary. Galvanised electrical conduit is galvanised thin-wall steel conduit for electrical raceways, protecting insulated conductors / cables - not a fluid-carrying pipe. The boundary, from the commentary to GB 50303-2015 clause 12.1.2: "thin-wall steel conduit in this clause means steel conduit with wall thickness less than or equal to 2 mm; wall thickness greater than 2 mm is called thick-wall steel conduit."

2. The minimum-wall floor (GB 55024-2022 clause 6.2.1, conduit wiring of cables in dry indoor locations). Original wording: "1 Where metal conduit wiring is used, the wall thickness shall be not less than 1.5 mm; 2 Where plastic conduit is concealed, conduit of not lower than medium duty shall be selected." Commentary: the minimum wall thicknesses for surface and concealed conduit in dry indoor locations - thin-wall galvanised steel conduit is acceptable for metal conduit, but with wall thickness not less than 1.5 mm, and rigid plastic conduit not thinner than medium-duty conduit; the minimum is set to safeguard circuit safety, deter scrimping and substitution, and ease site supervision.

3. The jointing ban (GB 50303-2015 clause 12.1.2, a mandatory provision). Original wording: "Steel conduit must not be butt fusion welded; galvanised steel conduit, or steel conduit with wall thickness less than or equal to 2 mm, must not be sleeve fusion welded. Extent of inspection: 20% of the total conduit joints of each inspection lot, covering the different jointing methods, not fewer than one of each. Method of inspection: observation during construction." Commentary (why fusion welding is banned): fusion welding causes burn-through and internal lumps that damage insulation when wires are pulled, and conduit cast into concrete lets grout water in and blocks it; even skilled welders with gas-shielded welding plus destructive weld sampling are unnecessary and uneconomic for building electrical raceways. Mature alternatives: threaded, set-screw and compression-gland connections.

4. Workmanship detail (DB11/T 1832.17-2021 clause 8.5.1, dominant control items). Key points: "1 Metal conduit must not be butt fusion welded; galvanised and steel conduit under 2 mm wall must not be sleeve fusion welded; 2 Galvanised steel pipe and flexible conduit must not have the earthing bond fusion welded. Where dedicated earthing clips bridge, the wire between two clips is a copper flexible conductor of cross-section not less than 4 mm2; the bond must not be coiled; 3 Non-galvanised steel pipe with threaded joints has the earthing bond welded at both ends of the joint; galvanised conduit with threaded joints fixes the bond with dedicated clips at both ends; set-screw steel conduit (JDG) joints are coated with electrical compound and may omit the bond; 4 Conduit must not be laid directly against walls and soffits." Clause 8.5.2 (general items), related requirements: welded steel pipe inside and out receives corrosion protection, and pipe buried in concrete at least inside; pipes entering floor-standing cabinets, consoles, boxes and panels rise 50 mm to 80 mm above the base face; buried outdoor cable conduit is at least 0.7 m deep; metal conduit under 2 mm wall must not be buried in outdoor soil; sleeved set-screw steel conduit (JDG) joints are tightened with the dedicated tool until the set-screw snaps off and the locking head turns home; surface-laid fire-protection circuits are painted with fire-resistant coating; exposed and damp locations use hot-dip galvanised electrical conduit of wall thickness not less than 2 mm; flexible conduit to driven equipment is the waterproof type with matching fittings.

5. Quick memory of the classes. Galvanised electrical conduit = thin-wall (2 mm or less, not under 1.5 mm), indoor dry raceways, mechanical joints. Galvanised steel pipe (SC on drawings) = thick-wall (over 2 mm), for damp locations, direct burial, explosion protection and civil defence. Set-screw (crimp) thin-wall steel conduit (JDG / KBG) = thin-wall, set-screw / crimp joints, the common modern substitute. Quota items usually split along these three classes - whichever name the drawing uses, take that class of item, never mix.

Applicability Boundaries

• The 1.5 mm floor comes from GB 55024-2022 clause 6.2.1 and applies to conduit wiring of cables in dry indoor locations; exposed and damp locations and outdoor burial carry stricter rules (hot-dip galvanised electrical conduit of wall thickness not less than 2 mm; metal conduit under 2 mm not buried in outdoor soil) - do not extend 1.5 mm to all locations.
• The fusion-welding ban admits no exemption by diameter or thickness: all steel conduit - no butt fusion welding; galvanised steel conduit and conduit of 2 mm wall or less - additionally no sleeve fusion welding. Galvanised and flexible conduit must also not have the earthing bond fusion welded.
• Item 4 comes from the Beijing local standard DB11/T 1832.17-2021, a regional code; other regions follow their local workmanship codes, local standards and design requirements - check the local volume notes for cross-region pricing or tendering.
• This card settles only "what galvanised electrical conduit is and its thickness and jointing requirements"; diameter selection (fill factor), quantity measurement and quota item rates are on other cards.

Further Reading

• GB 50303-2015 Code for Acceptance of Construction Quality of Building Electrical Works, clauses 12.1.1 and 12.1.2 and commentary (conduit laying, jointing process, thin-wall / thick-wall definitions).
• GB 55024-2022 General Code for Building Electrical and Intelligent Engineering, clause 6.2.1 (fully mandatory) and section 6.2, wiring systems design.
• DB11/T 1832.17-2021 Construction Technology Code for Building Works, Part 17: electrical power installation, clause 8.5.1 (dominant control items) and 8.5.2 (general items).
• For the naming of SC conduit, welded steel pipe, galvanised steel pipe and hot-dip galvanised welded steel pipe see the companion card "Sorting out SC conduit and galvanised steel pipe names"; for raceway quantity measurement and wire-pipe diameter selection see the companion cards.