Separate current transformer?

[Skywave]

Originally Posted by dominicbeesley

I'm not a fan of RCD's: I'd prefer them to be the last resort - I've had a 30mA belt, up a ladder, and I didn't like it one bit.

30 mA? How do you know it was 30 mA? I would have thought that that amount of current would cause you to thrown off the ladder! I did an experiment recently on an RCD to determine how effective it was to protect me from accidental shock. At 2 to 3 mA, the shock really hurt! And, of course, the RCD did not trip. That's not to criticise RCDs. I expect / hope an RCD to protect me from a shock of such magnitude that it will save me from being killed by electrocution. (But I'm not going to experiment at that level of current! )

Al.

[dominicbeesley]

30 mA? How do you know it was 30 mA?

The spec of the RCD. It may have been more momentarily but 30mA's what it said on the box. I may have had more than 30mA as I seem to recall the spec saying something like trips in <200mS at 150mA or 30mS at 30mA - or something close to those the times may have been different but I remember it needing to be 5x the rated current to get the lowest time!

As a youngster I once got "stuck" to a live feed and it was not pleasant. I'd have liked an RCD then but as a first line defence I'd rather avoid getting the belt in the first place. With a klutz like me a live chassis is just asking for trouble.

[Skywave]

The lethality of an electric current:

https://sciencebasedlife.wordpress.c...efore-you-die/

Al.

[Red to black]

Originally Posted by dominicbeesley

The spec of the RCD. It may have been more momentarily but 30mA's what it said on the box. I may have had more than 30mA .

An RCD does not limit the magnitude of shock current available only the duration. The rating eg. 30mA only denotes the threshold or I delta n the nominal current it is set to trip at.
It is the speed of operation (disconnection speed) that is the potential life saver, ie, within 300ms @ Idn X1 (30mA) and within 40ms for Idn X5 (150ms) for a 30mA RCD/RCBO to BSEN 61008 and BSEN 61009 non-time delay types.
It is possible even probable to briefly experience the full fault current available in the finite time it takes until the device trips.

Edit: it is possible to get a current limiting of sorts if the device happens to trip within the time taken to reach the peak of a half cycle of the AC waveform, but as these are by nature an electro-mechanical device the current versus trip time is far from linear, and even then you hit the time limit it takes to mechanically disconnect regardless of the magnitude of current.

[suebutcher]

Originally Posted by Ed_Dinning

Hi Sue, I'm sure we would be interested in hearing more about this repair café when it is set up.
Ed

The Daylesford repair café went well, and we had at least ten people wanting electrical appliances looked at. Much to my surprise, I fixed a PlayStation that had been jammed by a sticky DVD label. Nothing else, though; the big problem at the moment is all the different types of security screws found on modern equipment. I don't have the drivers to get inside half the stuff that was brought in. There's Torx, and the central pin version of that, I can find those, but what are the three-blade and the forked-screwdriver types called?

[TonyDuell]

Security screws are a right pain and they turn up where you least expect them.

As well as security Torx (with the central pin), there's also a similar version of the Allen Hex screw.

The 3-bladed version of Phillips/Pozidriv is TriWing I think.

I know the forked ones, but I can't remember what they are called.

Then there's Torq, a sort-of off-set Phillips.

I have this set from Wera :

http://products.wera.de/en/kraftform..._62_kk_62.html

which I found on my father's bench after he passed away. I am still using it of course.

There are also 5-point versions of the Torx, known as TS, for example :

https://www.machinemart.co.uk/p/clar...r-set-ts-star/

And then there's System Zero, which I believe was designed to be almost impossible to remove without the right tool, such as :

https://uk.rs-online.com/web/c/tools...=system%20zero

[Ed_Dinning]

Hi Sue, I call the 3 bladed ones Isle of Man types.

I found some good sets of screwdrivers on the web, they were for mobile phone repair and I think Jay-car have something similar for not too much.
I'll probably call in when I'm over there next year.

Ed

[suebutcher]

They're listed as TriWing, I'll ask the organisers to look for those as well as Security Torx. Apparently the Americans call the forked driver system "snake-eyes". Sometimes you can get these moving with circlip pliers if the screw's not deep set.

[Refugee]

I just ground an old flat blade screwdriver to make the forked tool and have been using it for ages.
When I go for a bit of modern kit I sometimes end up with a number of power tools with different tips in them to avoid wasting time changing them all the time.

[Terry_VK5TM]

Surprisingly, I got a screwdriver set (interchangeable bits) with just about every type of security screw head in Bunnings a few years ago and not expensive either.

Don't know if they still have them.

Otherwise, try Jaycar or Altronics.

Make sure you get a set with long shafts for the deeply set screws.

[Refugee]

Our local flea market has loads of sets and they cost so little that each likely work place gets a kit bunged into its tool box.

[dseymo1]

Yes, I too have a couple of sets of interchangeable hex-fit bits which cover all the larger security screws I've come across, plus a precision miniature driver set, which again has a range of bits to meet most eventualities.
I'm not sure how much use 'security' fastners really are when the appropriate bits are so readily available! Only those whose heads snap off intentionally when torqued-up seem anything like secure.

[Refugee]

Back in the 1970s I spotted some wood screws with the flats to tighten them but ramped so that they could not be removed.
You would have had to drill them out and remove the remains with grips.

[suebutcher]

I've seen those around. Fortunately they're not common!

[Refugee]

Drills are common enough to sort them out so perhaps that is why I have not seen them since the 1970s.

[trsomian]

The problem with the sets of "security" bits is that sometimes they are not long enough; the "security" screw(s) is at the bottom of a hole may be 2" deep or more and little larger than the diameter of the screw head