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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Plasticizer problem
"Ron Jones" wrote in message
... Dr. Barry L. Ornitz wrote: "N Cook" wrote in message ... snip About the only way to prevent plasticizer damage to other plastics is to keep vinyl products away from them. Most coaxial cables for radio frequency use have a center conductor insulated with polyethylene, a wire braid shield, and a plasticized PVC jacket. When the plasticizer leaches from the jacket into the polyethylene, its electrical losses increase greatly. One modern innovation uses either aluminum foil or metalized polyester to wrap around the braid preventing the ingress of the plasticizer. But it also provides better shielding allowing the braid coverage to be lessened from 90 to 95% coverage to less than 75% coverage leading to a much lower weight. The problem occurs in all sorts of areas - leisure boats on UK canals are generally steel, and so have thick polystyrene insulation against the hull, then covered with wood panels. All cables running in this space have to be run in a conduit, as it was found that the polystyrene would suck all the plasticizer out of the cable making it brittle and liable to break without warning. Thanks for the follow-up, Ron. I know that polyvinyl chloride has been banned from many applications in Europe. I believe that this is because most garbage is incinerated in Europe. I guess that PVC wire insulation is still permitted. Here in the USA, electrical conduit is often made of PVC. I do not know if quenching agents are used here to reduce the limited flammability even more. PVC is also used extensively for plumbing. In both cases, little or no plasticizer is used. But PVC is also used in most wire insulations, and plasticizer is used here. Rigid polyurethane foams are usually used for home construction and I do not believe that plasticizer leaching will cause major problems to these foams. But polystyrene foams are used occasionally and your warning is an excellent one. While I am familiar with many IEC standards, my knowledge of electrical wiring for Europe is limited. Here in the USA, we have what is known as THHN (Thermoplastic High Heat-resistant Nylon-coated) wire. This utilizes a thin, colored PVC insulation clad in a Nylon jacket. It is frequently used in conduits because of the ease with which it can be pulled without abrading the insulation. I suspect that the Nylon will provide a good barrier to plasticizer migration too. [UL (Underwriters Laboratories) lists THHN as oil resistant to 60° C.] -- 73, Dr. Barry L. Ornitz WA4VZQ [transpose digits to reply] |
#2
Posted to sci.electronics.repair
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Plasticizer problem
Dr. Barry L. Ornitz wrote:
"Ron Jones" wrote in message ... Dr. Barry L. Ornitz wrote: "N Cook" wrote in message ... snip Thanks for the follow-up, Ron. I know that polyvinyl chloride has been banned from many applications in Europe. I believe that this is because most garbage is incinerated in Europe. I guess that PVC wire insulation is still permitted. Here in the USA, electrical conduit is often made of PVC. I do not know if quenching agents are used here to reduce the limited flammability even more. PVC is also used extensively for plumbing. In both cases, little or no plasticizer is used. But PVC is also used in most wire insulations, and plasticizer is used here. Rigid polyurethane foams are usually used for home construction and I do not believe that plasticizer leaching will cause major problems to these foams. But polystyrene foams are used occasionally and your warning is an excellent one. While I am familiar with many IEC standards, my knowledge of electrical wiring for Europe is limited. Here in the USA, we have what is known as THHN (Thermoplastic High Heat-resistant Nylon-coated) wire. This utilizes a thin, colored PVC insulation clad in a Nylon jacket. It is frequently used in conduits because of the ease with which it can be pulled without abrading the insulation. I suspect that the Nylon will provide a good barrier to plasticizer migration too. [UL (Underwriters Laboratories) lists THHN as oil resistant to 60° C.] As I said - this is for boats (that of course vibrate - and cables getting brittle - even 12V ones are not a good idea). Not sure what "standard" mains wiring is made of - web sites tend to say things like "BASEC approved 6242Y Twin and Earth cable. Grey sheathed with harmonised core colours. BS 6004". Which is not a lot of help. They are probably reluctant to give too much info, as the rules (here) are now that mains wiring be only carried out by a electrican.... Nanny state.... -- Ron Jones Process Safety & Development Specialist Don't repeat history, unreported chemical lab/plant near misses at http://www.crhf.org.uk Only two things are certain: The universe and human stupidity; and I'm not certain about the universe. ~ Albert Einstein |
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