JDG conduit (sleeved set-screw galvanised steel conduit): its definition, the "thin-wall 2 mm or less" boundary, the twist-off set-screw jointing process, the bonding-jumper practice, permitted and prohibited locations, and the distinction from KBG conduit and SC pipe

Topic Positioning

What JDG conduit is - the definition, jointing process, bonding-jumper practice and permitted / prohibited locations of sleeved set-screw (galvanised) steel conduit, and its distinction from KBG conduit and SC pipe. For reading electrical raceway drawings, selecting materials, workmanship and pricing.

Core Conclusions

1. Definition and the "thin-wall" boundary. JDG conduit = sleeved set-screw steel conduit, thin-wall galvanised steel conduit for insulated conductors in electrical circuits (trade name "set-screw conduit"); with KBG conduit (sleeved crimp-type thin-wall steel conduit) it belongs to the thin-wall class, a lightweight substitute for thick-wall SC welded steel 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." The same clause (a mandatory provision of that code): "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: 20% of the conduit joints of each inspection lot, covering the different jointing methods, not fewer than one of each. Method: observation during construction." - the very reason thin-wall conduit must use set-screw, crimp and other mechanical joints (commentary: fusion welding burns through and leaves internal lumps that damage insulation when pulling wires, and conduit cast in concrete lets grout water in and blocks). Item 1 of clause 8.5.1 of DB11/T 1832.17-2021 repeats the ban: "metal conduit must not be butt fusion welded; galvanised and steel conduit under 2 mm wall must not be sleeve fusion welded."

2. Jointing process (set screw tightened to twist-off). DB11/T 1832.17-2021 clause 8.5.2 item 8: "when sleeved set-screw steel conduit (JDG) is jointed, the dedicated tool shall tighten the set screw to twist-off and turn the locking head home." DB51/T 5047-2007 clause 14.3.18 on set-screw joints: "the set screws of sleeved set-screw conduit runs shall be operated with the dedicated tool. The screw heads must not be hammered, cut or snapped. At the joint, both pipe ends shall be even, smooth, burr-free and undeformed. Before the pipe enters the coupling, the inserted end shall be clean, and the joint gap shall be sealed. The pipe shall sit tight in the coupling." It further reads: "for straight runs, both pipe ends enter the straight coupling to the middle, against the groove ends at both sides; after positioning with the set screw, tighten until the screw head shears off"; "for bends, both bent pipe ends enter the coupling grooves; after positioning with the set screw, tighten until the screw head shears off"; "where the diameter is 32 mm and above, each end of a set-screw coupling shall carry not fewer than 2 set screws. The set screws shall be in visible positions."

3. Bonding jumper. DB11/T 1832.17-2021 clause 8.5.1 item 3: "non-galvanised steel pipe with threaded joints has the bonding jumper welded at both ends of the joint; galvanised conduit with threaded joints fixes the jumper with dedicated earthing clips at both ends; set-screw steel conduit (JDG) joints are coated with electrical compound and may omit the jumper." Item 2: "galvanised steel pipe and flexible conduit must not have the jumper 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 jumper must not be coiled."

4. Installation requirements (T BCQMS 02-2024 clause 9.2.4, original). "Installation of sleeved set-screw steel conduit shall comply: 1 sleeved set-screw steel conduit must not be laid within equipment foundations of buildings or structures, and must not be used outdoors, in civil-defence works, damp environments, or flammable or explosive locations; 2 at run joints, electrical compound or other sealing and waterproofing measures are preferred; at connections to boxes and enclosures, claw-type nuts shall lock onto the threaded conduit couplings; 3 exposed conductive parts of the run shall be reliably earthed and must not serve as continuation conductors of the earthing wire."

5. Prohibited and restricted locations, summary. (1) Sleeved set-screw steel conduit must not be laid in equipment foundations and must not be used outdoors, in civil-defence works, damp environments or flammable and explosive locations (T BCQMS 02-2024 clause 9.2.4); (2) metal conduit under 2 mm wall must not be buried in outdoor soil; exposed and damp locations use hot-dip galvanised electrical conduit of wall thickness not less than 2 mm (DB11/T 1832.17-2021 clause 8.5.2 items 7 and 11); (3) the fellow KBG conduit, by DB32/T 4071-2021 clause 4.2.18: "sleeved crimp-type thin-wall steel conduit (KBG) may be laid concealed, surface or above ceilings indoors, and in hot, dusty, vibrating or fire-risk locations, but must not be used in acid, alkali or salt corrosion or explosion-risk locations."

6. JDG / KBG / SC comparison.

Trade name	Formal name	Jointing	Position
JDG	sleeved set-screw (galvanised) steel conduit	set screw tightened to twist-off, dedicated tool	thin-wall (2 mm or less), surface or concealed indoors in dry locations
KBG	sleeved crimp-type thin-wall steel conduit	crimping tool, not fewer than two crimp points	thin-wall, same class as JDG
SC	welded steel pipe (thick-wall)	threaded / sleeve joints	wall over 2 mm

KBG crimp jointing (DB51/T 5047-2007 clause 14.3.18): "with straight couplings, the coupling length is 2-3 times the pipe OD and the pipe ends sit at the coupling midpoint. With 90-degree elbow couplings, the pipe ends enter the elbow sockets fully before crimping with the crimping tool, with not fewer than two crimp points. After crimping, lead paint is applied at the joints so the whole run forms one continuous earthing body." The same clause on threaded couplings: "threads must not be crossed and the couplings must be through-threaded. After fitting, the pipe ends align with not more than two threads exposed."

7. Beijing quota items. Beijing 2024 general building services consumption standard DB11/T 2382-2024 table C.4.91-4 "set-screw (crimp) thin-wall steel conduit" - surface laid on brick and concrete, nominal diameter within 15 mm, item C4-11-119, unit m, work content "positioning, marking, drilling, clipping, sawing, pipe fitting, jointing, fixing, installing fittings etc."; its material column already contains JDG (KBG) thin-wall conduit (1.0300 m/m), JDG (KBG) straight coupling 15 (0.1648 No./m), JDG (KBG) threaded box connector 15 (0.4120 No./m), JDG (KBG) pipe clip 15 (1.4420 No./m) etc. - JDG and KBG share the table; the couplings and clips are included in the laying item and take no separate item.

Applicability Boundaries

• The "thin-wall 2 mm or less" boundary comes from the commentary to GB 50303-2015 clause 12.1.2 and applies to conduit-laying acceptance under that code; the fusion-welding ban admits no exemption by diameter or thickness - all steel conduit bans butt fusion welding, galvanised steel conduit and conduit of 2 mm wall or less additionally ban sleeve fusion welding, and galvanised pipe and flexible conduit further ban fusion-welded jumpers.
• JDG conduit is thin-wall galvanised steel conduit for surface, concealed or above-ceiling laying in dry indoor locations; it must not be laid in equipment foundations of buildings or structures and must not be used outdoors, in civil-defence works, damp environments or flammable and explosive locations (T BCQMS 02-2024 clause 9.2.4).
• Metal conduit under 2 mm wall must not be buried in outdoor soil; exposed and damp locations use hot-dip galvanised electrical conduit of wall thickness not less than 2 mm (DB11/T 1832.17-2021 clause 8.5.2).
• DB11/T 1832.17-2021 (Beijing workmanship regulation), T BCQMS 02-2024 (Beijing association standard), DB51/T 5047-2007 (Sichuan) and DB32/T 4071-2021 (Jiangsu) are local or association standards - regional regulations; check the current local regulation and design requirements for cross-region pricing.
• This card settles only "what JDG conduit is, how it joints and where it is used"; 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 (thin-wall / thick-wall definitions, the fusion-welding ban and its reasons).
• DB11/T 1832.17-2021 Construction Technology Code for Building Works, Part 17: electrical power installation, clause 8.5.1 (dominant control items: jointing and jumpers) and 8.5.2 (general items: JDG jointing, pipe-end and burial-depth requirements).
• T BCQMS 02-2024 Standard for Quality Evaluation of Beijing Building (Great Wall) Premium Works, clause 9.2.4 (set-screw conduit installation and prohibited locations).
• DB 51/T 5047-2007 Construction Technology Regulation for Building Electrical Works, clause 14.3.18 (threaded couplings, sleeve welding, crimp and set-screw jointing).
• DB32/T 4071-2021 Regulation for Construction and Acceptance of Urban Landscape Lighting Works, clause 4.2.18 (KBG permitted and prohibited locations, corroborating).
• DB11/T 2382-2024 Construction Works Consumption Quota Standard, Annex C general building services works, table C.4.91-4 "set-screw (crimp) thin-wall steel conduit" (item C4-11-119 etc.).