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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Default 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

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Default 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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