Table 41.1 Assumed Touch Voltage

The 13th Edition of the Regulations for the Electrical Equipment of Buildings, 1955, required the use of Voltage Operated Earth Leakage Breakers if the loop impedance was too high to allow reliable operation of fuses or circuit breakers. Reg.410. 


Reg. 406 recommended that a maximum Voltage of 40 Volts be tolerated on exposed earthed metal and consumer's earth terminal under fault conditions.


Edit. Add. The 1975 edition of the booklet by Crabtree entitled "The Protection of Domestic and Industrial Installations" 1975, 6th edition, mentions both Voltage and current operated earth leakage circuit breakers for protection of hand held appliances and reduced fire risk. (B.S. 842; 1965 and B.S. 4293 1968. respectively). The normal out of balance operating current for current operated devices was typically 500mA at the time. 25mA high sensitivity devices were also available.


Mention in the Crabtree publication of 50mA being the lower limit of lethal current.


Edit 2. Add. The 14th Edition 1966 I.E.E. Regs. mentions current operated earth leakage circuit breakers. My copy is dated 1976.

Reg. D.24 required that a current operated earth leakage circuit breaker should only be used where the product its operating current in Amps. and earth loop impedance in Ohms does not exceed 40.


Z.

The South African goldmines were test beds for the early ELCB's, an interesting article is below: -

https://cbi-lowvoltage.co.za/sites/default/files/downloads/TechPapers/CBI2.pdf

The rise and rise of the Wylex 1980s' R.C.D.

https://www.flameport.com/electric_museum/wylex_fuse_boxes/wylex_wses802_rcd.cs4


Z.

mapj1:

Well, being old enough to remember 1981, though not old enough to vote at the time...

From which we can deduce that Mike is a mere slip of a lad and no more than 57 years old. ?

... in the same way we had folk telling us not to include the area of the lawn in the 100m2 served by the ring, even if the socket for the lawnmower was say a socket by the back door. 

(if you do include the lawn area you find it plays havoc with the diversity and maximum demand sums.)

So for your Zoomup-style quiz of the weekend ...


When I returned from letting out my house circa 1990, the lawn had been tonsured as it were, i.e. the mown area was semicircular. The rest was what we would nowadays admire as a wild flower meadow area. Why?


P.S. Not an RCD in sight!

a lawnmower, or strimmer, or WHY on a 50 m lead covers a semi-circle of about 4000 m².


But does not need 40 off 32A ring final circuits to provide the power to it, which the 100m2 rule may suggest...


Nor is it feasible to consider it part of any well earthed equipotential zone. Indeed if you stick two electrodes in 50m apart there is a sporting chance of finding them a few volts apart even when nothing much is happening, from currents passing through, even before you introduce any faults of your own.

There is a very good reason that lawnmowers, strimmers etc are double insulated, not earthed metal, and it is a pity that electric car makers have not followed suit - it would have been technically harder to make a double insulated switch mode power supply for a few KW, but by no means impossible to arrange.

Mike

PS..
From which we can deduce that Mike is a mere slip of a lad and no more than 57 years old. ?

Thank you. I think.  I was born in 1967 so a mere 54 if that helps you narrow it down. (and despite the grey hair and all the rest, I still got asked 'are you over 18' by what looks like a schoolchild at the checkout when buying paint thinners. )

ProMbrooke:

Well, I'm prepared to show my inference in great length, for the world to see, for the benefit of all humanity. :) Hiding the technical reasoning is both a crime and unethical when used to make what is used as law all over the globe. And I know why the IEC has gone into hiding technical aspects: because AFDDs are just the start to a long marketing concept. If you can mandated it, then it will sell. But that is for another thread.

[yes - I've been waiting for news on the AFDD thing...?]


I agree that the ideal standard would come with clear explanation of the reasoning behind it - though not necessarily in the same document. That would help avoid poorly founded rules appearing in the first place, make it easier to contest ones that do slip through, improve understanding of the purpose of rules and so of what consequences any considered deviations might have, and possibly help a later generation of standards-makers who've forgotten the original reasoning.

However, it would doubtless take a lot more work to give clear explanations of the typically messy problems involved, e.g. where a standard is a compromise between various national practices. Perhaps it would be enough to have clear minutes of all discussions that result in changes, rather than having to produce a nicely illustrated and described work like this TR 1200-413. Minutes wouldn't have to identify the parties, but just the arguments and choices.

On the other hand, journals are increasingly wanting authors of articles to declare any interests that might affect their opinions, and - for the reasons you've given - there's as much or more reason to care about this with standards. So perhaps it would be better to require more detail of the people present, their allegiances, and their side in the decisions. This gets more foggy with international bodies that take representatives from countries rather than directly from organizations. One sees less clearly who's pulling the strings to sway a country's view, unless it becomes appallingly obvious as with the ms-oxml & ISO case. (Not to mention the non-proportionality of representation of population when countries have populations from under a million up to hundreds (and more) of millions.)

The money side is a trouble, too. Standards end up out of reach for most except the companies that have to have them. They typically refer to many others, which in turn refer, so that many have to be bought. Years ago I took a course about one standard from its main contributor, who had a slide showing the many-inch tower of paper you would have to buy in order to have this standard with all its parts and the other standards that it depends on: he referred to the organization that produced it by making a slow, heavy circular motion with his hand, explaining that he was turning a money-making machine (he was a German-speaker - perhaps it's an established gesture).  Everyone I know who's contributing to IEC standards is paid by their employer, which also then pays for the IEC standards it uses. Perhaps I'm unrealistic to think the remaining costs should be low enough to be easily covered by e.g. countries paying a small amount, so that all the standards (besides the details of how they arose) could be freely viewed by anyone... BS7671 is actually cheap, due to its application, history, etc.; but buying all its parts from IEC would very much not be.  There are many other standards that don't have a convenient, cheapish national compilation of the parts.


Interesting points on the times and voltages.  I can't let myself get properly started on that now, as I'll take too long.  The chosen approach in IEC is much about simplicity of defining and verifying the requirements (e.g. loop-test, fuse/breaker curve). 

The handle cranking money making machine is indeed a common gesture in certain circles. ? (I did do quite a bit of standards related work for Siemens Mobile and then the base station part for a  while in the early 2000s). Having worked on standards for 3G telecoms (3GPP) it is much the same in process as you describe  but much cheaper. The interested parties, the telcos, the manufacturers of handsets and some national bodies like Ofcom and the occasional "independent" ? from a security related organisation  are all paid for by their organisations, and generate the content of the standard in effect for free. The ETSI did some editing, merging and admin to do with version numbers, between meetings, and the standards appear  free to download on the internet shortly before the next meeting to change them again.

I firmly believe that  if it was not for the problem of paying for those extra folk in the chain who feel entitled to a regular income and have become accustomed to a rate of spend that matches it, you could do the same with the IEC stuff.