[chbot] Knob shafts / extensions and insulation

Mark Beckett m.beckett at amuri.net
Wed Aug 31 06:44:11 BST 2016

If the mains and the other parts are seperated, then it is permissable 
... however.
While the physical mains and the rest can be seperated, how about the 
electrical side.

ie if you have a mains transformer/rectifier/regulator in one side, and 
pass the DC component thru, then it's fine.
If you are doing some mains sensing and there is a risk of part of the 
other side becoming live if someone swaps the phase and neutral, then NO.

Plastic extension or a plastic knob will work, but the issue is whether 
these have any sort of voltage rating.
I know there used to be some used for tuning/adjustments on high voltage 
transmitters, etc, but these don't exactly fit an encoder.

In most cases the shaft of the encoder is not physically touching the 
contacts, so in theory your first layer of insulation is there.
The plastic knob/extension becomes the second layer.

Don't forget the big Danger 230v do not open while live, no user 
servicable parts etc ...  for those that can't read.

For your other project, I'd avoid any sort of physical contact.
I've seen the use of a Hall effect switch used to retain the 
waterproofing, so maybe this could solve the problem.


Mark Atherton wrote:
> Found some plastic shaft units:
> Search "EC12 encoders" on AliExpress, or eBay
> My fav on AliExpress "8 foot long shaft encoder 16 files 25MM"
> http://www.robotshop.com/en/parallax-incremental-rotary-encoder.html
> http://www.robotshop.com/en/5v-mechanical-quadrature-encoder.html
> HTH, Mark
> On 30/08/2016 11:28 PM, Volker Kuhlmann wrote:
> > I'm planning to put a mains voltage circuit into a suitable box with
> > clear lid. One knob will have to come out through the lid. I'd like a
> > rotary encoder with push switch - unfortunately, push switch and 
> plastic
> > shaft seem to be mutually exclusive. I can't find plastic shaft
> > extensions either.
> >
> > Is it permissable to stick a metal shaft out through the lid, assuming
> > the mains voltage side is appropriately insulated and tied down?
> >
> > Suppose in another project a capacitive power supply is sufficent, and
> > Arduino runs on mains potential. Does anyone know a clever trick to
> > use a metal shaft encoder here (without surgical replacement and 3D
> > printed parts)?
> >
> > Thanks,
> >
> > Volker
> >
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