Author Topic: Strain relief - worn wire  (Read 633 times)

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Offline vjekobalas

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Strain relief - worn wire
« on: January 27, 2022, 03:07:13 pm »
I am replacing all the cables in this ultrasound head (my daughter's beauty parlor/don't ask) as the insulation, shield and one wire have broken in one cable and all the cables are stiff presumably from heat near the ultrasound head.

Was wondering whether anyone has any idea how I could improve the strain relief/lessen the wearing of the cable(s).

Let me explain the photos:
Photo 1 - Here we see the ultrasound head with top shell
removed and the cable which is broken (arrow points just after
it's strain relief). The break occurs somewhere just after
what I named as the "coupling" as it couples the top and middle
shell. This cable as well as four other cables and the
polyurethane pipe pass through the flexible plastic conduit
which is strengthened/supported with steel wire as can be
seen on the photo. These cables/pipe pass tightly through the
conduit i.e. little space for movement. The plastic tie near end of the conduit
I presume both helps a little so there is less motion of the
cables and stops the conduit from moving back through
the coupling.

Photo 2 - Here we can see the break in cable and the
flexible spring like support for the whole cable (same
support is at other end)

There are traces of some type of grease along the
wires presumably for pulling the cables/tube through
(not looking forward to this) and maybe to lessen wear
in case of any movement.

What is strange to me is that although I see a slight wear on the
conduit at exit from coupling, I don't see / feel any abrasive
surface and the wires are quite tight in there not being able
to move - what could cause such a break in the cable and is there any
wise I could do to avoid or reduce reccurence ?

Offline mastershake

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Re: Strain relief - worn wire
« Reply #1 on: January 28, 2022, 02:36:32 am »
this happens to my wife's clippers as a dog groomer the cords do this all the time from just tons of use. i like to use different sizes of heat shrink. so what i mean is i start with a 1" piece over where the most tension is, then a 2" piece over that and further down. then a 4" piece over that etc if needed. then it gets sandwiched between the case layers with a knot at the top keeping it from pulling out. this is a bit different situation. but this lasts for usually 2-3 years of daily use before i have to fix it again (she uses them 8 hours a day every day). there has to be movement normally for a break like that to happen even if small. either the wire or maybe the sleeve moving. the wire tie is prob there to prevent it from pulling out of the "coupling" its possible its chafing on the grey sleeve. another thing you can try as long as this doesnt get to warm you can try to fill the grey tube with silicone or hot glue once you pull the wife through to keep the wire off the edge. i wish i could explain it better. tough without having it in hand. could be a number of ways to skin the cat if you will.

Offline vjekobalas

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Re: Strain relief - worn wire
« Reply #2 on: January 28, 2022, 06:40:19 am »
Could you please clarify:
The heat shrink is placed over the tension area as per my attached sketch
and is it not heat shrunk/why (I presume the string is needed only for this reason) ?


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