Two technicians are discussing shielded cable. technician a says that shielded wires are generally twisted in pairs to cancel the effect of electromagnetic interference. technician b says that shielded cable can be replaced with regular straight wire once the vehicle is out of warranty. who is correct?

Technician A is Correct. So this is actually a question I just had come up in my IT-140 Networking Fundamentals class but as a matter of fact I also know this because I've worked as a Network Technician for many years now both as a salaried employee and as an Independent Contractor. The reason Technician A is correct is because, indeed Wires in a Shielded Twisted-Pair (STP) cable or even Unshielded Twisted-Pair (UTP) cable are intentionally made this way for two reasons: the expressed purpose of actually twisting the wires in the first place is to protect them from interference called "EMI" (as stated in the question, Electromagnetic Interference!), however they are also twisted this way because of a similar interference (and in most cases, classified as the same kind of disturbance) called RFI or Radio Frequency Interference. As a technician, one of my jobs was hanging Access points in ceilings, and a requirement of that particular job was to make sure that these cables (which in this case were Cat6 which is short for Category 6, the exact cable that is referred to in the question, because Category 6 cable is shielded) were not to be left laying on the ceiling tiles in the drop ceilings! The reason being is, the light fixtures have electricity running through them, and anything with electricity running to it gives off Electromagnetic Interference. So, again Technician A is correct but... I have to say this as a side note... it would be completely pointless and utterly time consuming to remove these cables and replace them with a straight wire just because the warranty expired on a vehicle. Besides... Straight Though Wire and Twisted Pair are used for two completely different things.

Hope this helps! If you'd like to fact check me, google "emi interference"

CJ

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-ttl