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xpd



The Overrated Raccoons
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Topic # 189613 6-Jan-2016 11:55
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Wow.... me in the home workshop forum, thats scary considering I cant even hammer a nail straight.

Anyway, putting in some of that Expol type insulation under the house, and theres a label on it saying to use polyester tape to cover any electrical cabling near the Expol to prevent possible arcing - fair enough.

But how many layers of polyester tape do I need ? Just a single layer is enough ? 

Also, Im planning on running CAT5 through the same area, do I need to insulate that with tape as well ? One of the cables will be PoE for the Unifi AP.



TIA





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  Reply # 1462235 6-Jan-2016 11:59
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The problem is the PVC will mix with the polystyrene and make a sticky mess that has lower insulation properties and may fall apart if moved after its sucked all the plasticisers out of the PVC cable insulation.

Same as when people put computer stuff back into polystyrene packaging without the plastic bag and the cables go all gross.

Not sure what the tape is made of to stop it happening, most insulation tape is PVC as well so I would have thought it would be affected too.




Richard rich.ms

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  Reply # 1462241 6-Jan-2016 12:04
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The issue is the electrical insulation will become brittle over time if it is in contact with the styrene*

But looking at that joist is it 150mm? With 50mm expol there may be a healthy gap between that and the cable. Does it actually touch the cable when installed?



*edit: go with richms on that one ; ).

 
 
 
 


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  Reply # 1462242 6-Jan-2016 12:08
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The "possible arcing" is a bit of a misdirection, the cables become brittle due to exposure to the expol polystyrene

You don't need to use tape, newspaper or an air gap will also solve the issue...

Polystyrene  in direct contact with PVC (the insulation around the wiring) - can result in the cable PVC becoming brittle as the plasticiser reacts with the Polystyrene,

BUt yip it also applies to data cables

http://www.generalcable.co.nz/getattachment/0ebda90b-b4f8-43ae-b622-c9280295116b/PVC-Cables-in-Contact-with-Polystyrene-or-Bitumen.aspx

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  Reply # 1462247 6-Jan-2016 12:18
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Just to clear up the confusion there, the plasticisers migrate out of the cable causing the sticky outside. The loss of plasticiser makes the insulation brittle.

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  Reply # 1462248 6-Jan-2016 12:20
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So long as there is something between the two, I should be fine. Cool, will use the tape I have (will double layer it) and newspaper for the rest ;)





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  Reply # 1462251 6-Jan-2016 12:29
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Just did this job last week on my 'holiday'

There's brown wax-paper type stuff in each packet of Expol. Looks pretty low tech but presumably it does the trick if they include (imagine the lawsuits if it failed and led to a fire. I usually use PVC insulation tape to hold the wax-paper in place, that way the wax paper is doing the isolation between materials, and the insulation tape is redundant once the polystyrene wedges the wax paper in place

Edit: I have heaps left over as there was only 2m of electrical cable under the house (mostly wired in the ceiling) so could post it to you in an envelope if you need extra, or looking to complete this stage of the job before filling your house with large polystyrene bricks

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