Computing stuff tied to the physical world

RCD finally in

In Hardware on Dec 10, 2010 at 00:01

Remember the weblog post about mains voltage and my plan to work on some circuits involving high voltage?

Well, with fear and trepidation I can announce that the missing link has finally arrived:

Dsc 2397

That’s an “Aardlekschakelaar” in Dutch, i.e. a Residual-current device.

People are probably either very thankful or very afraid of this thing, judging by the number of acronyms under which it is known: RCD, RCCD, RCCB, GFCI, GFI, or ALCI – take your pick!

An RCD continuously compares the current in with the current out, and breaks the circuit once the difference exceeds a certain threshold. I decided to get the most sensitive one I could find, which trips at 10 mA. I’m terrified of electric shock – especially the non-lethal kind… (no idea about the other variant, and I intend to keep it that way).

Ok, so it took over a month from ordering the RCD to getting it delivered – from a mail-order company here in the Netherlands, go figure. I’ll build the RCD into my super-duper isolation jig as soon as I find some time. I sure don’t want to fiddle with 230V while distracted or in a hurry.

Speaking of which…

There are a large number of people waiting for orders from the JeeLabs shop right now, for which I offer my sincere apologies. The reason is not really lack of time (well, maybe a little…), but the fact that stocks have run out on several items. I’ve got just about everything that’s missing on order right now, but in some cases my hands are tied because things don’t always arrive as quickly as promised or expected.

I’ve been refraining from sending out partial shipments, because it doesn’t really make much sense most of the time (sending out a JeeNode without the matching JeeLink, for example), and because it adds substantially to my overhead. Which is of course my own concern, but it also raises the chance of mistakes, something which I really want to avoid.

Not everything is in yet, but I hope to have just about all shipments ready by this weekend. Please get in touch if you’d rather have a partial shipment sent out soon, rather than waiting until next week. There will be no extra charges for such split shipments.

Crazy times around here. And the long-overdue server migration isn’t making it any easier!

P.S. Don’t get me wrong. I’m still working on quite a bit of fun stuff on the side, so let me finish this slightly panicky post with a little smiley anyway :)

  1. Does that mean that we are going to see an AC Dimmer plug-in soon? /me ducks and run :)

  2. What’s that “super-duper isolation jig” all about?

  3. I am pretty sure that with your isolation transformer, it is impossible for an RCD to improve safety. Do not forget that neither protects you if you touch the two live wires simultaneously. Be careful.

    • Yes, as I wrote this post, I started wondering myself. I came to the same conclusion: there is no scenario where the 10 mA current would trip the RCD: touch one wire is safe either way, and touching both is as dangerous as before!

      Ok, thanks for confirming this. It goes to show how quickly you can get a false sense of security…

    • Yes but if you are working without an isolation transformer or you want to test an unknown variable transformer an RCD is a nice to have item.

  4. nice. how do you manage to make such great pictures? what’s your setup ? i always get horrible lighting and focus :D What mail-order company did you use ?

  5. @adilson – sure, with “soon” undefined, I have no problem confirming that :)

    @reinhard – just a description of the isolation transformer I’m setting up.

    @mihai – this was actually hacked up with a diffuse lamp, normally I prefer to use daylight.

    • just a description of the isolation transformer I’m setting up

      Two transformers back to back like mine ?

  6. Hi JC,

    I was also wondering what the added value of the RCD was for a specific setup you had in mind, couldn´t think of one…. Thx for the update on the shipping part, already had plans to send you an email today to check on it. Now I´ll wait till next week…;-)

  7. @jcw As long isn’t soon as in Duke Nuken Forever soon, I’m fine with it :)

  8. I’m also working on main current prototypes and looking for a totally safe solution. I’ve seen somewhere a guy using a bulb lamp, supposed to limit the current (used in the same manner as a fuse). Would it be reliable?

    What about using a small UPS (<300W). Should not this limit the current available?

    • 300 W is 1.3 A @ 230 V => lethal

    • A 25W bulb will limit the current to at most some 100 mA @ 230 V. It also drops the voltage, which means the circuit won’t see a stable 230 V supply (anything between 0 and 230 V, in fact, depending on current draw).

      For really low-power experiments, a 7W lightbulb might be a good idea. But same here: the voltage will collapse completely if you draw any serious amount of power.

      There’s no way to make it safe. Power is there to, ehm, power stuff. And there not really a way for the power source to distinguish between a nice light bulb and your heart, fibrillating…

  9. I have a similar fuse type for my workbench power. It is called differential fuse around here. Mine triggers at 30mA though.. Now that I’ve seen yours triggers at 10mA I wonder how safe is mine.. I’ve read on some website that 30mA AC can cause severe pain..

  10. 30mA is standard required in all sockets, 10mA is mostly used in wet enviroments, sauna, pool, bathroom circuits. the only safe way to go is to be carefull !!! but why do you need such a thing ?don’t you mostly work with 12V ? this is safe by all means

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