Instrumentation marshalling boxes

[Buzz1980]

Hi Hope someone can help answer below ?

I have had a few views on how best to terminate our marshalling boxes for instrumentation panel wiring. As you will be aware the instrumentation wiring has screens which are either individual or overall screens in 20 pair cables. Now on some jobs that I have been on when the cables enter the marshalling boxes they take off the inner insulation say 25mm as it enters the enclosure then put a piece of self amalgamation tape over the crutch of the cable and sleeve the overall screen. The foil of all the individual screens is kept on and dressed up to the terminations then the foil is stripped off 30mm from termination then self amalgamation tape over then connect the pair and individual screen into the terminations, screens are sleeves also, the foil has plastic also over the paired cables before being stripped at terminations. Also seen where they strip all the foil off right down to the crutch then self amalgamation tape over each of the pair and then dress up. I would just like views on what others do and if it is just down to engineering preference?

 

[Lucien Nunes]

I don't like self-amalgamating tape. I put silicone sleeving over the drain wires, then secure with expandable (Hellermann) sleeves at the crutch and the end of the pairs. If the foils are at risk of damage or it is important to prevent contact with each other if the melinex film gets breached, I over-sleeve the pairs. Ideally, when finished it should be impossible to bridge together or make contact with screens at any point, even if you probe the bundle with a meter probe.

 

[pc1966]

I would agree with @Lucien Nunes that self-amalgamating tape is not a good choice here. My usual approach is heat-shrink, but you need to take real care as some cable's insulation will melt at temperatures not much over what is needed to shrink the sleeving.

Also check with the designer if there is any need (or definite need not to) attach any overall screening braid to any metal box entry via a suitable gland for good EMC performance.

 

[nicebutdim]

Not sure I'd want to heatshrink control cables, when sleeves can be fitted in seconds.

Some of these and one of these in appropriate sizes (alternative suppliers and better prices are available).

 

[Buzz1980]

Thanks for the replies guys, yeah just seeing which way other people do it, the foil is all protected by the wrap around plastic, then hellermann at just before entry in to terminals, I think it looks neater this way and also saves time in stripping all the foil off when inside floor to ceiling marshalling boxes, just didn’t know if there was any engineering reason behind it ? Why lads do it differently ?