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Acrylic as an Insulator

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Brian H30/06/2021 14:24:21
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I need to make a very small electrical switch; is acrylic (Perspex) suitable for insulation at low voltages i.e. 5v to 9v?

Brian

Michael Gilligan30/06/2021 14:33:15
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Very suitable, Brian

See list of values, here: **LINK**

https://omnexus.specialchem.com/polymer-properties/properties/volume-resistivity

… look for PMMA

MichaelG.

Emgee30/06/2021 14:33:35
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Yes Brian

Emgee

JasonB30/06/2021 15:16:18
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Corian works well too and the colours can look like old Bakelite if it's for the Ford.

Brian H30/06/2021 15:39:48
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Many thanks for the answers, I knew that I could rely on this site!

Yes Jason, it's for the Ford and I have a colour picture showing that the switch is black and I just happen to have a piece of black Perspex.

Brian

old mart30/06/2021 18:53:32
3317 forum posts
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If you have a digital meter, set it to 20 megohms and test that black plastic, it is very unlikely to be a conducting grade, but, being black, it could be antistatic, there is a remote possibility.

Edited By old mart on 30/06/2021 18:54:55

Brian H01/07/2021 08:11:42
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Thanks for the info Old Mart, I hadn't considered that, I'll dig out my old Avo.

Brian

Joseph Noci 101/07/2021 08:36:56
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Posted by old mart on 30/06/2021 18:53:32:

If you have a digital meter, set it to 20 megohms and test that black plastic, it is very unlikely to be a conducting grade, but, being black, it could be antistatic, there is a remote possibility.

Edited By old mart on 30/06/2021 18:54:5

An Urban Legend that...

If there are any carbon chains in that sort of coloured material, they never are in contact and never form a continuity path in the material below the hundreds of meg-ohms region. Any finger grime on the material will conduct more than the material innards!

The same applies to Anti-static bags ( for electronic components, etc) - the pink, black and silver bags that are common in the field have a spec to which compliance is required - clean with alcohol and then distilled water, warm to 35deg C for 1 hour, and resistivity must be such that less than 1nanoamp will flow with 1000VDC applied to two 1cm contacts spaced 20mm apart...

So the possibility of conduction in black perspex is not even remote.. - @ 5V you could use a bit of Tomato Box...

Joe

Jeff Dayman01/07/2021 12:41:34
2169 forum posts
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Hi Joe, Just FYI resin manufacturers do offer many types of conductive injection moulding grades of engineering polymers. Sabic alone offer 211 grades, Link below. Some are very conductive.

https://www.sabic.com/en/products/specialties/lnp-compounds/lnp-stat-kon-compound

However it is very unlikely you or the OP would find scraps of one of these carbon fibre loaded polymers (or the more recently developed RGO graphene loaded ones) in your local signmaker's shop, hobby store, building supply, or industrial plastic sheet supplier. Many commonly available PMMA and polycarbonate dark colours use chemical dye for colouring them rather than solid pigment, these materials have very low conductivity as you said.

On many of Henry Ford's cars until the mid 1920's, wood was used as low voltage switch gear insulator material, and after that, compression moulded thermoset phenolic resins became commonly used, one brand being Bakelite.

Brian H01/07/2021 15:24:12
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Just tried my AVO on the black acrylic and there was no reading at all. I also tried the AVO on other items just to make sure that it is working (it is).

There is a board on the back of the Ford with ignition connections and that is definitely wood. Here is a link to the slide in the Henry Ford museums website showing the switch in question.

https://www.thehenryford.org/collections-and-research/digital-collections/artifact/252049/#slide=gs-212199

Any comments would be welcome.

Brian

JasonB01/07/2021 16:14:04
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The Perspex should work fine for that, maybe a quick rub with some Scotchbrite to knock off the gloss and it will look like the Bakelite type material.

Brian H01/07/2021 17:46:41
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Good idea Jason, I'll do that.

Brian

Michael Cox 101/07/2021 19:01:36
544 forum posts
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The only problem with acrylic as an insulator is that it has quite a low softening temperature. This makes it usuitable for situations exposed to heat or where the switch may get hot. In these situation phenolic plastics like bakelite , Tufnol and Paxolin are better as they are much more heat resistant.

Mike

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