'Bridged' Ring Final Circuits

[Paul_C]

I suppose one also has to consider what one means by a 'mistake'. If, as so far remains the case, no-one can find a way in which such a circuit is non-compliant with BS7671, in what sense is it 'a mistake which has to be rectified'?

And even if it doesn't comply with BS7671, that doesn't mean one should assume it was a mistake. I might well do all sorts of things which don't comply with BS7671, but they won't be mistakes - Just aspects of the design and installation that I considered to be more suitable to the task at hand.

 

[Electrifying]

......as far as I could make out (by application of engineering logic), a ring with bridges is no less safe than one without bridges (and, indeed, on the contrary, it seemed to me that the existence of bridges would tend to have beneficial, rather than detrimental, effects).




.....I was thinking more about the 'books' - many of which say or imply that a bridge is a 'serious problem', some of them citing the 'broken ring' scenario as being the reason a bridge is dangerous (even though you and I agree that it is no more dangerous than a break in a ring which doesn't have bridges)

Sorry, John, out of order to even suggest this.

In your engineering logic this might make sense.......but in the real world, of course a ring final with a bridge would be more dangerous.

Why? - Because in the real world an electrician has to test that ring final -

The first test of which is end to end continuity.

If there's a break in a 'normal' ring final this will show up on end to end tests.

If there's a break in the outer ring of a 'ring final' that contains a bridge, then end to end testing will appear 'normal'.

If you know what you are doing, your next set of 'tests' (figure of 8 ) will reveal results that point to a 'ring within a ring' (bridge).

If you don't understand the readings, or, due to the layout, they are too close to what the readings should be anyway, and you don't realise there is an 'interconnection', then you could go away leaving a DANGEROUS fault on the circuit.

You could not then just note these results at each socket and leave it at that.....because there could be that break in the outer ring.

So you have to adjust your testing procedure and re-test end to end continuity to make sure it encompasses the whole 'ring'.

That, is the danger....not the 'coding'.

 

[JohnW2]

.....I was thinking more about the 'books' - many of which say or imply that a bridge is a 'serious problem', some of them citing the 'broken ring' scenario as being the reason a bridge is dangerous (even though you and I agree that it is no more dangerous than a break in a ring which doesn't have bridges)

Sorry, John, out of order to even suggest this. In your engineering logic this might make sense.......but in the real world, of course a ring final with a bridge would be more dangerous. Why? - Because in the real world an electrician has to test that ring final - ....

What you say would be perfectly correct if you added ".. and some (but we don't know which!) so-called 'electricians' are not adequately competent (safe enough) to test ring final circuits in the presence of the 'unexpected' ".

Your statement then becomes true, but frightening. As I've said umpteen times, I'm not suggesting or advocating that anyone deliberately includes bridges in ring finals. What I am doing is acknowledging that, as we all know, these bridges do already exist (created 'accidentally', or whatever). As you very correctly go on to say...

The first test of which is end to end continuity. If there's a break in a 'normal' ring final this will show up on end to end tests. If there's a break in the outer ring of a 'ring final' that contains a bridge, then end to end testing will appear 'normal'. If you know what you are doing, your next set of 'tests' (figure of 8 ) will reveal results that point to a 'ring within a ring' (bridge). If you don't understand the readings, or, due to the layout, they are too close to what the readings should be anyway, and you don't realise there is an 'interconnection', then you could go away leaving a DANGEROUS fault on the circuit.

...which, as I said, is just frightening, since that is a situation which is 'already upon us'. Any so-called 'electrician' who had that lack of understanding ("did not know what (s)he was doing" in the presence of a bridged ring final), and therefore who could "go away leaving a DANGEROUS fault on the circuit" might tomorrow walk into some house with such a circuit and then walk out leaving that dangerous fault. A person who is not capable of detecting a dangerous situation and fault with which they could be (unknowingly) confronted any day obviously does not deserve to be called an electrician, should not be working as an electrician and most certainly should not be trusted to test ring final circuits.

Hence, I suppose I have to agree with you. If we have to assume that electricians may be incapable of detecting a dangerous fault on a ring circuit which has a bridge, I suppose we have to regard such bridges as potentially dangerous - but that's because of the existence of frighteningly incompetent electricians, rather than the bridge, per se. As for the 'electricians' to whom you refer, if they are not competent/knowledable enough not leave that dangerous fault undetetected, then what, if any, electrical work can/should they be trusted to do - and. most important for Joe Public, how is one meant to distinguish between such a dangerous 'electrician'and someone who actually knows what (s)he is doing?

Kind Regards, John.

 

[bernardgreen]

I suppose we have to regard such bridges as potentially dangerous - but that's because of the existence of frighteningly incompetent electricians, rather than the bridge, per se.

Precisely. A bridged ring does not present any greater safety hazard than the same ring unbridged. In some circumstances the bridge will balance the loading in the two cables from the CU

So you have to adjust your testing procedure and re-test end to end continuity to make sure it encompasses the whole 'ring'.

The difficulty is detecting that there is a a bridge. Using "normal" end to end testing is not going to find a bridge unless it is close to the CU and the resistance readings are obviously too low for the length of cable involved to reach all the sockets known to be on the ring.

- and. most important for Joe Public, how is one meant to distinguish between such a dangerous 'electrician'and someone who actually knows what (s)he is doing?

It is said that members of schemes are well trained, informed and as such cannot possibly create new or not notice existing hazards.

Yet I have yet to meet one ( not that I meet many ) who understands how to use voltage drops along a cable to map out interconnections between sockets.