Why is it necessary to use dual cables in some designs? And how should the wires be connected?
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I saw many designs on the drawings; for example, the calculated current for 325A requires that the cable be constructed using (3*150+2*70) in a dual-strand configuration. I would like to ask why this design was chosen Are there any particular considerations? What are the things to keep in mind when laying it? Also, how do I wire it to the circuit breaker? If others say that additional extended copper bars are needed, then how should they be added? It would be best to have picture explanations. Thank you!
This is generally done for thicker cables; otherwise, if a cable is too thick, it becomes difficult to manipulate it when turning it or doing similar actions. GB 50217-2018, Code for Design of Cables in Electrical Engineering, 3.6.11: When the AC power supply circuit is composed of multiple cables connected in parallel, the cables should preferably be of equal length, laid in a similar manner, and should use conductors of the same material and cross-section ； For cables with metal sheaths, the metal material and cross-sectional structure should also be the same. I don’t understand the specifics of the construction process either.
It is not necessarily necessary to use additional extension copper bars; I have seen ones that are installed at the same point. Of course, such copper bars are a bit longer than normal and have several screw holes. Dual-cable connections can be made either to the same screw hole or to different screw holes on the same copper bar
Well, then I have many more questions. First, is it allowed to connect two cables together at the same point? I’m not sure if this is mentioned in the guidelines ； Then, some switches simply cannot accommodate dual terminals, so it is necessary to find a way to add external copper bars ； Also, I’m not sure what you mean by those several screw holes – are they referring to the holes in the upper part of the nose? If a copper bar has several wiring holes, how are the two wire ends connected? Also, if there are too many holes in the copper bar, it should affect its current-carrying capacity, right? If all these issues are resolved, I think the problem will be solved.
1. The cable cross-section is too large, making construction inconvenient； 2. Save costs. The cable cross-section is chosen to be very large, which increases costs, but the current-carrying capacity does not increase in proportion to the enlarged cross-section. For example, the flow capacity of two 150 dual-pipe units is greater than that of one 300-unit unit. 3. Special circumstances. For high-power induction motors, the cross-sectional area of the single wire is too large, while the cable connection port in the motor’s junction box is too small to accommodate it.
I’ll take some pictures for you tomorrow; I’m not quite sure about the specific requirements.
Ah, so many pictures! Thank you so much! I will download the image and save it. But I have a problem with this diagram: since the small copper bars running downward are quite long and need to be fixed to the brackets, there is an issue of insulation between the busbar and the brackets. It’s not clear from the diagram how this insulation is handled
Oh, okay, thank you so much! These diagrams are very useful to me; they help me see things more clearly. Thank you again!