On the differences between steel conduits and metal cable trays
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The GB 50303 2015 Code for Acceptance of Construction Quality of Building Electrical Engineering states that steel conduits shall not be connected by butt welding； Galvanized steel conduits or steel conduits with a wall thickness of 2 mm or less shall not be joined by sleeve welding ； However, the GB 50168 2018 Standard for Construction and Acceptance of Cable Lines in Electrical Installation Projects requires that metal cable conduits should not be welded directly; instead, threaded connectors or sleeve-sealed welding methods should be used ； When connecting, the two pipe ends should be aligned, the connection should be secure, and there should be good sealing ； The length of the threaded joint or sleeve should not be less than 2.2 times the outer diameter of the cable conduit. I’ve always thought there are conflicts in the regulations ； Today, a colleague mentioned that steel conduits and galvanized steel conduits are designed for use with wires (cable conductors) inside the conduit, while metal cable trays are intended for use with cables inside the conduit. I would like to ask the experts how they interpret this
In my opinion, for metal protective tubes, whether wires or cables are used inside them, the construction requirements should be the same.
@btlhrdb2008 Thank you for your participation. If the construction requirements are the same, why do the requirements in different national standards vary? I checked the construction requirements for cable conduits in the GB 50093-2013 Code for Construction and Quality Acceptance of Automated Instrumentation Projects, and they are also different from those in the previous two standards. What is the thinking of the standard-setters? Why are no uniform requirements and regulations set forth in the standards for the same type of construction objects? How do everyone understand it? Please share your thoughts freely. In the project I’m working on now, some of the plant owners and supervisors require welded connections for the sleeves, while others demand threaded connections. The construction requirements vary from one unit to another within the same project, and it’s not possible to standardize these requirements or make adjustments based on the actual conditions on site; even installing protective tubes proves to be a complicated task.
Take a close look at the regulatory provisions to see if there is a difference between “casing” and “conduit”
For exposed installation of galvanized pipes, threaded connections using sleeves are generally used; this approach is common in explosion-proof environments. Where wire ducts can be used, they are typically employed instead； Underground protection pipes cannot be connected by threading. Generally, sleeve welding is used, but GB 50303 seems to prohibit the welding of galvanized pipes; therefore, in such cases, welded steel pipes are chosen and treated with anti-corrosion measures. The standardization you speak of is what we desire!
When welding galvanized pipes, the galvanized coating at the welding site must be removed; otherwise, bubbles, porosity, and false welds will occur. It also makes the weld brittle and reduces its stiffness. Furthermore, corrosion occurs at the welds, destroying the anti-corrosion function of the galvanizing. Therefore, when welding galvanized pipes, threaded connections are mostly used.
From a professional perspective: I think it’s best to first examine the conditions related to electrical piping, and then decide which standard is more applicable – either the Building Electrical Code 50303, the Electrical Installation Code 50168, or the Explosion-Proof Electrical Code 50257. However, on-site, one also needs to take into account the feelings of the owner and the supervisor; that’s how things are for the construction contractor.