IEC 60364 Table 48A

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ProMbrooke:

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I've long proposed discarding the emphasis/focal point of earthing and bonding and rather creating a new, third central pillar of source loop conduction theory, which rooted in admittance on the basis of protecting life and property rather than having earth electrodes and connecting metal things to one another.

What is "source loop conduction?". How does it work? Or is it just something that The Dr. and Rose Tyler would come across?


B.S. 7671 already covers safety of installations.


Reg. 131.1 "...intended to provide for the safety of persons, livestock and property against dangers and damage which may arise in the  reasonable use of electrical equipment."


Z.


 

Source loop conduction is the idea that high admittance between the line and CPC/metal work at any point that a fault  is capable of occuring can trigger disconnection of the over current device rapidly enough to prevent physiological harm and fire to the property.


Basically a more evolved theory of ADS.


I know BS7671 covers protection of life and property.

I'll stick with the approved, tried and tested systems in place at present thanks, not some unproven, unconvincing and unworkable "theory".


Z.

Then we can be friends :)

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ProMbrooke:

Also this video. Most importantly around 25 minutes in, the author shows a breaker tripping magnetically vs thermally:



https://www.youtube.com/watch?v=emxfsOUTkUg

Yeh, but the fire was started by a propane torch not an electrical arc. Why worry about electrical arcs when the fire has already been started by another cause? Illogical.


Edit, add.


In the U.K. we have the wonderful 13 Amp. plug made to B.S. 1363. Have you ever heard of it? It contains a fuse. The fuse rating can popularly be either 3 Amp or 13 Amp, but other sizes are available like 5 Amp or 10 Amp. Flexes are protected by these fuses which are less in value than the 20 Amp circuit breakers referred to in the dated video.


Z.

Illogical indeed, but sadly this was enough to get AFCIs taken seriously.


Of course I've heard of BS 1363 plugs. AFCIs were supposed to to mimic their their ability of clearing flex faults rather quickly.

AJJewsbury:

Source loop conduction is the idea that high admittance between the line and CPC/metal work at any point that a fault is capable of occuring can trigger disconnection of the over current device rapidly enough to prevent physiological harm and fire to the property. Basically a more evolved theory of ADS.

It sounds like the ADS part of the old EEBADS approach - or is there more to it than that?


(I've got in the back of my mind that Earthing is more than just about triggering ADS - it also keeps the entire LV system at a known voltage w.r.t. the general mass of the earth, and prevents it being dragged to other voltages by other systems - e.g. by capacitive coupling to HV circuits via the supply transformer, or other near-by systems -  protecting not just people from shock by the insulation of the conductors too.)


  - Andy.

Can you go into more detail on the EEBADS approach?

mapj1:

The thing about the Pace consulting notes and the you tube videos is that they relate to 110V land, where installation practices are very different. 

I do not think you could set fire to a UK extension lead in a cardboard sandwich  and expect it to remain live and sizzling for very long at all, certainly only a few seconds, not minutes.

230V land regulations actually require us to verify Zs, and the L-N equivalent when we test PSSC, and that coupled with the maximum voltage drop specification, pretty much assures that any LN or LE  short circuit or fault of fractional ohms will trip the breakers quite promptly. The higher voltage lower current also helps with that.

Now of course there are always corner cases that will struggle, one might be a 50m extension lead snaking down the garden in skinny 1.5mm2 cable - being near that 16 AWG example,  perhaps plugged into a socket already marginal on voltage drop at full load. (so about an ohm there and back in the cable), and if the VD to the socket is the max of 5% (12V) at 13A (then a further ohm or so for that)  Here the PSSC at the end of the extension lead may be as low as 100A.

However while the 32A C type will be well on the thermal curve and may not fire until about 10 seconds, it is more likely to be a B type, and that will prompt -trip in many cases, and even if it does not, then the  13A fuse in the plug will get you within 3 seconds at 100A.


The US centric sizzling faults are not the kind seen here - the cables that stay live tend to blow to clear.

Mike

Alright, it seems we're all on the same page. And I'll add that not only is EFLI  is none existent in NFPA-70, but the CPCs are also grossly under sized. Just don't say that on a US forum.


So my question is: why are AFDDs being mandated through out the IEC market place?

Can you go into more detail on the EEBADS approach?

AJJewsbury:

Can you go into more detail on the EEBADS approach?

You're making me feel old now!


EEBADS = Earthed Equipotential Bonding and Automatic Disconnection of Supply - what ADS was referred to in years gone by (but long after the period where regs required some earthing, and perhaps a limit on the resistance between parts within an installation, but without any particular requirement for disconnection). The EEB bit got dropped from the name - possibly due to the fact that bonding doesn't really create a true equipotential zone (at least not where large fault currents are involved - Ohm's Law gets in the way), plus of course we sometimes don't even attempt to create an equipotential zone (outdoors for instance), but still have ADS.


   - Andy.

Thanks :)


And I agree much that same with all your points.

15^th Edition Regulations (1981) 

Regulation 413.7 required metal parts within the equipotential zone to be supplementary bonded to maintain the equipotential zone, where those parts:

1. Are extraneous-conductive-parts, and

• Are simultaneously accessible with exposed-conductive-parts or other extraneous-conductive-parts, and

• Are not electrically connected to the main equipotential bonding by permanent and reliable metal-to-metal joints of negligible impedance.