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Inline Key Switch or Tamper Resistant control for mains devices?!

shabaz

Hi,

For one reason or another (elderly relative), I'm looking for a way to prevent operation of a mains appliance (about 6A at 230V AC) unless, say, a key of some sort is inserted, to prevent them from using the appliance themselves. It doesn't need to be a high-security solution, it could simply be a plastic key for instance, that could be pushed in and rotated, to enable the appliance.

I don't wish to cut holes in the appliance, and really do want to do this inline with the mains wire. 

Is there any existing product that could do this? If not, is there any suggestion that I could fit into a small plastic enclosure myself? I don't have access to a 3D printer, so it ideally needs to be a solution that I could make using conventional tools (electric drill, saw, etc). 

One way I can think of, is to find some sort of enclosure where a rocker switch could be fitted recessed, and then have a small padlock such that it prevents the switch from operating. But it probably requires a custom box : ( Another way could be to have a Bluetooth controlled relay. I could design this, but I'd rather find an off-the-shelf solution. 

I'm sure I can't be the only one wanting to do such a thing, but I'm having no luck googling for this. 

Anyone come across anything that could help?

  • 0 in reply to shabaz
    shabaz said:
    I'll see if I have a plate.

    Cheapest source for that type of plates, is a set of plastic kitchen cutting boards. Either in  a 1£ shop, or at a flea market, you'll find enough material for years.

  • 0 in reply to beacon_dave

    Can omit the outside edges of the slot if you want. Easier to cut manually and can use a wider range of padlock thicknesses. 

  • 0 in reply to beacon_dave

    I gave it a try today, with a slight variation that makes it quicker to construct:

    image

    I used 3mm plastic, and this seems to be sufficient for preventing a plug from functioning, however the spec should be examined really. Perhaps 4 mm plastic would be better.

    I have not made the holes for the padlock yet, because Amazon let me down with their delivery. However I'm confident that part will work fine once I've made the holes for it!

    image

    For the holes, they were spaced 22.2 mm from their centres, with the earth pin having a 9 mm hole, and the other two were 8 mm diameter.

    The plate was 100 x 60 mm, but I think 110 x 70 mm could be better (impact the switch on the socket more!). The two plastic strips were 10 mm wide.

    I really like this design, and the flat plate impacts the on-off switch on mains sockets too, making it even harder to switch on.

    I'm going to suggest this as a product for a family member (who has the right machinery!) to construct and sell, if they are interested (and obviously you should get some sort of a royalty  although I hope they sell it at ultra-low-cost). Even if it just sells in the few dozens or hundreds, it's still a great problem-solver for those who need it. I've no idea if the family member would be interested in productizing this, but if they do, then it's a nice option for users, to either self-construct as an open-source design, or simply buy it.

  • 0 in reply to shabaz

    Looks good.

    Might have to be careful of the plastic thickness as if too thin then it may flex too much and allow the pins to be released, or if it is too brittle then it may be too easy to snap. Originally I was thinking around 6mm as a starting point but would take some experimentation.. 

     

  • 0

    thinking outside the box here:
    - what if you put a europe connector (£2) on them, and hide the euro-to-uk adapter (< £5)?

    This may work in an environment with elderly ... and all components are off the shelf

    additional asset: it doesn't look like a lock, so your elderly family members might not feel "being guarded"

  • 0 in reply to shabaz
    shabaz said:
    one could produce a better and more robust design perhaps.

    I don't think that robustness was a design criteria. It's about signaling that it should not be used. And forcing people to override security measures to use it anyways. And that would make them liable.

    That often works in professional settings, where you can write procedures / rules with consequences. 

    It does not look like a solution to keep people out that want to get in. But they can't do it without showing that it's hampered with.

    It's like a "top secret" stamp on a file, with a wax seal. The stamp or seal  don't physically stop you from opening the file and reading / copying / stealing the content.

  • 0 in reply to Jan Cumps

      100%.  Lockout/Tagout devices are basically a professional agreement not to kill each other.  They keep honest people honest and well meaning people from accidently killing a maintenance worker.  They are intended to prevent inadvertent re-energization of a circuit under maintenance.

    Security devices are far more robust.  And... there are those work environments where a security device or multi-layer de-energization is more appropriate.  In high voltage work, even though the line has been de-energized, the line crews earth all of the lines on both sides of the work zone.

      How aggressive is your nemesis? Relaxed

  • 0 in reply to Jan Cumps

    I was unclear, I meant robust as in not breaking in normal use (the hinge looks uneven, as if it is fatigued). I figured the manufacturer probably doesn't mind if the installer has to buy replacements eventually! 

    However some plastic hinges last for ages even when they appear white and stretched, so I can't be sure if I'm making the wrong assumption and it may last for ages.