White T&E - Advice on a rewire

[securespark]

Same with plaster. Pink oop North, grey down South.

 

[crystal ball]

Same with plaster. Pink oop North, grey down South.

It was always grey round here, finish, bonding now its pink

 

[ebee]

Grey for a long time then pink later on, dare I say white one coat too

 

[securespark]

It was always grey round here, finish, bonding now its pink

Which bit of the country are you in?

 

[JohnW2]

Well yes i do not disagree with that,in essence, however even loading throughout the ring should be attempted in order to avoid overloading or large amounts of load bias even if not overloaded would be expected to enhance life of cables to nearly forever.

Is there any evidence that occasional relatively short-lived high currents less than the cables alleged 'CC@ (or even a little over that) have any significant impact on cable life?

I say "occasional relatively short-lived" because, as I said previously, in the (very common) case of Method C 2.5mm² rings, one would need in excess of 2 x 3kw (or 3 x 2kw) loads very close to one end of the ring for any of gthe cable to be overloaded, and I very much doubt that would often happen, and certainly not for 'an appreciable period of time' in domestic installations.

You almost seem to be implying that minimising the current in any part of the cable will improve life expectancy, even if (as is common) it is nearly always appreciably, maybe considerably, below the cable's 'CCC'. Do you believe that and, even if you do,is it really relevant since we seem think that, "in normal service" PVC cable probably has a longer life expectancy than the average human being? !

Simple thoughts of a quick in yer head nature are usually all that are required or even back of a fag packet if you like. There is no need to make great reams of calculations to acheive this aim. Two simple rules cover its (providing that total ring overload has been dealt with) 1/ even spread around the ring and/or 2/ most loads around the middle one third of total ring length and then you should have a ring that lasts a long time and no particular portion aging much more rapidly than the remainder.

You are, of course, only able to make such comments because you are talking about rings. The cable does not know whether it is part of a ring or radial circuit but, in the latter case, one cannot usefully 'spread the load around the circuit' (current-wise) and nor is there any significance of "the middle third" (or any other portion) of a radial circuit - with a radial circuit which has multirole connected loads, the current carried by the cable just progressively increases as one gets closer to the origin of the circuit, with the circuit's entire total load current going through the cable near to the origin.

It's obviously impossible for a designer to design a sockets circuit 'as they would like', since they can't know what will be plugged into which sockets. If one (i.e. 'the regs') wanted to avoid the possibility of loads (no greater in total than the design current of the circuit) resulting in 'overload' of part of the cable in a ring final "because it was a ring final" then that could be achieved by specifying an (easily calculated) minimum distance (as a proportion of total ring length) between any socket an an end of the ring.

Kind Regards, John

 

[ebee]

Yup. The aim is to make current time broadly similar tgroughout, that could go towards not overloading any part of the ring , keeping ring length (or radial length as well) to a reasonable minimum will also help with volt drop and fault clearing (at least earth faults with fuses anyways) ..

It was not unknown around here , back in the day, for folk to use 3kw fan heaters and again some used tgree or even four on one ring, some folk had tge trusty old immersion heater attached to the ring in those days, it was by no means uncommon.

So, we gets into the habit of giving things a thought, by the way a designer might stab aan informed guess of which sockets are more or less likely to be used for which items or groups of items. Certainly by no means foolproof but they would give a passing thought to likelihoods of usage and even make a kind of vague attempt to axtive6ly encorouge or discorouge some things to some extent. I must admit that i was unconvinced of such influencing but some seem to believe it .

 

[JohnW2]

Yup. The aim is to make current time broadly similar tgroughout, that could go towards not overloading any part of the ring , keeping ring length (or radial length as well) to a reasonable minimum will also help with volt drop and fault clearing (at least earth faults with fuses anyways) .. .... It was not unknown around here , back in the day, for folk to use 3kw fan heaters and again some used tgree or even four on one ring, some folk had tge trusty old immersion heater attached to the ring in those days, it was by no means uncommon.

As I said, designers cannot 'design properly' when one is talking about a sockets circuit, the use of which is beyond the designer's control. As you say, they can only guess about likely usage.

Accordingly, these discussions can only really take place with the caveat that the total load on the circuit does not exceed the design current (i.e. OPD rating) of the circuit, since otherwise it gets silly - just 3 x 3kW fan heaters would overload a 32A circuit even if all were applied in the middle of a ring or 'evenly distributed' around a ring. ... and, of course, most sockets circuits have enough outlets for a user to theoretically be able to plug in 200A + of loads

If one does stick with that caveat, then it is exceedingly unlikely that the CCC of any of the (Method C 2.5mm²) cable would ever be exceeded, since that would require that the 'full' 32A worth of loads be applied very close to one end of the ring - which I would suggest is an extremely unlikely situation.

However, again sticking with the caveat, what a designer could do is to position socket outlets on the ring such that it is impossible for the current in the short leg to exceed the cable's CCC provided that ('the caveat') the total load does not exceed 32A. With 2.5mm cable installed by Method C (CCC=27A) that's not very demanding at all, but sockets would have to be a bit further from ends of the ring if the installation method reduced the CCC (possibly to be the 'minimum permitted' of 20A).

Kind Regards, John

 

[crystal ball]

Which bit of the country are you in?

Cumbria

 

[ebee]

Cumbria. Often go and see the lake, nice run out for us then a stay overnight or sometimes two nights

 

[crystal ball]

Cumbria. Often go and see the lake, nice run out for us then a stay overnight or sometimes two nights

So do we, take the motorhome & EBikes, avoiding school holidays, stay at a site in Borrowdale set in the woods, on the last weekend of the season, hardly any one there, red squirrels, owls hooting in the night

 

[ebee]

Yep good, hope the weather is usually Ok with out of season, we usually stay overnight or two overnights sometimes in say a travelodge or guest house, nice run out in the country, avoiding motorways.
In fact when we go to Scotland we often favour the A6 rather than the M6, a lot of it runs close to the M6 crossing here and there and it`s not very busy, you can admire the views and see them all bumper to bumper on the M6. doesn`t take that much longer and a lot less hassle.

ho, Peak District and North Wales too, same there, avoids motorways and do a country run, calling in at Holmfirth where those dear three nutters Nutters were filmed.

No idea why Cumbria gets called "The Lake District" as it only has one lake, just like the Village next to us has just one lake and that does not get called the lake district for some reason. Strange world.

 

[ebee]

If one does stick with that caveat, then it is exceedingly unlikely that the CCC of any of the (Method C 2.5mm²) cable would ever be exceeded, since that would require that the 'full' 32A worth of loads be applied very close to one end of the ring - which I would suggest is an extremely unlikely situation.

I`m not disagreeing with you John, well not much anyway. Yes the loads we work to have safety factors worked into them anyway.
However, to run cable at less than the max stated much, if not all, of the time helps keep them cool because any conductor heats up when current flows. Therefore keeping nearer to minimums and avoiding maximums might help, can not hurt and might actually help prevent aging too.
Surely all those electrons banging around in conductors wears them out a bit? just like water travelling in a pipe/tube, to some degree/
Ring or radial applies the same, underload rather than overload is my motto. And anyway the benefits of a ring are surely starting to be lost if one leg is very much more loaded than the other?

 

[Adam_151]

As I said, designers cannot 'design properly' when one is talking about a sockets circuit, the use of which is beyond the designer's control. As you say, they can only guess about likely usage.

Though one should not worry too much about that, theres a lot of things in this world which cannot be "designed properly" however a competant designer will seek to produce an acceptable solution while minimising risk.

Engineering is the art of modeling materials we do not wholly understand into shapes we cannot precisely analyze so as to withstand forces we cannot properly assess in such a way that the public has no reason to suspect the extent of our ignorance.

Perhaps an sobering concept to think about as you board an airliner or visit a themepark