Why do instrument junction boxes need jumpers?
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I’ve always known that jumper wires are needed at the connections of the instrument junction boxes, but I’ve been wondering why that is and what purpose they serve The junction boxes are already connected to each other using connectors, which means they function as a conductor. If the goal is simply to make the junction boxes act as a conductor, then it seems unnecessary; but perhaps that’s what the standards require, without any specific reason. However, since there are standards, there must be a reason behind them – otherwise why would standards exist? I haven’t been able to figure this out yet. Everyone is welcome to share their thoughts on this
HGT 20513-2014 Specifications for Grounding Design of Instrumentation Systems
The term used in the standards is “should” rather than “must”, so it is also not necessary to use it
GB50303: But generally, chemical enterprises take precautions and still install it. In simple terms, it’s just an extra layer of protection with little cost involved.
You can’t take this too seriously, especially when some experts are doing the inspection
The 4th floor is the correct answer; this is the standard used by experts for their inspections
It seems like our two companies were inspected by the same expert team; P, we’ve just been found to have this problem
This post was last edited by hxch150804 on 2021-12-15 at 16:24. In fact, it’s somewhat similar to the static discharge connections used at the flanges of hazardous material pipelines in chemical plants – things like gas pipelines and coal gas pipelines. These measures are taken as a precaution; the goal is to prevent any potential accidents. There are cables inside cable trays, and if one of these cables gets damaged and starts leaking electricity, then that cable tray won’t be connected to other cable trays or to the pipe racks. In such a case, that cable tray becomes a live conductor, and touching it can be fatal. The purpose of making these connections is to allow any leaked electricity to be directed into the ground, which in turn causes the circuit breaker to trip, thereby allowing the problem to be detected. Invisible hazards are the most dangerous! So, there is not only bridging but also grounding
GB 50217 Code for Design of Cables in Electrical Engineering 6.2.9 Metal tray systems shall have reliable electrical connections and be grounded. When using fiberglass reinforced plastic cable trays, a dedicated protective conductor should be installed along the entire length of the tray. CECS 31 Code for Design of Steel Cable Trays 3.6.25 When a tray system is used to form a grounding circuit, the contact resistance at the connections shall be measured in accordance with Article 3.7.5 of this code; such resistance shall not exceed 0.00033Ω. What all these specifications emphasize here is a reliable connection. In the case of metal connectors, bolts, etc., used in cable trays or trunking, factors such as grease on their surfaces and gaps can increase the grounding resistance. Using jumper cables wrapped around the bolts to connect them to the cable tray or trunking serves the purpose of ensuring a reliable connection. This is similar to the original intention of the specifications, which detail the welding methods and weld lengths for the grounding grid flat bars.
If you want to use a jumper cable, then go ahead and do it; it’s no big deal. If you can’t repay the 2 trillion in loans, the worst that can happen is to give up trying – what else can you do?