I made no mention of your previous posts. I am just trying to get you to focus on the question at hand.
You are the one who mentioned "40A through your 26 amp cable" [sic]...
Oh, so you don't want to talk about "40A through your 26 amp cable" [sic] - ok so why mention it?
Its not an error dennis, it is something called hyperbole - a bold and obvious exaggeration intended to parody your keenness to over engineer everything regardless of technical merit.
Are they? Odd that because shower circuits are another good example of a situation where overload protection is not actually required since there are no likely failure modes or user actions that could result in overload. So long as the cable's current continuous rating exceeds the maximum demand of the shower, you can even have the circumstance where the MCBs nominal trip current is higher than that of the cables. Something to beware of when upgrading a shower to a more powerful one.
Both statements are incorrect, IMO, if taken literally.
It would be wrong to use 4 mm^2 cable in place of 2.5 if the enclosure and or the terminals were too small to avoid bending the conductors excessively tightly and/or to make sound connections.
It would be unsafe to fit a smaller breaker if this introduced the risk of tripping and the loss of power introduced danger - e.g. on lighting circuits.
Both you and adam bought up our previous discussion about spurs in a manner claiming i was wrong. You appear to think it applies here. I never said what you were doing here was wrong.
Now you are trying to divert attention from your error. It would make no difference to the safety of the lighting circuit if someone did wire the shower to it. The protection mechanism designed into lighting circuits will protect the circuit from the excess load. There is no need to over engineer anything as it is already correctly engineered. A point you obviously didn't know when you posted.
However if you connected exactly the same shower to a 2.5 mm2 spur (much bigger cable than lighting circuits) or even to the actual 2.5 mm2 ring then its not safe and not adequately protected either. There are allsorts of rules that the user has to apply to make rings and ring spurs safe, some of which have changed over the years. How many homes have spurs with two sockets on spurs? This used to be in the regs when the IEE thought it was safe. Now it is regarded as unsafe and you can only fit one. Even this is just a compromise.
Who is talking about shower circuits?
So you have never seen a shower where part of the heating element has shorted, lowering the resistance and increasing the load. Opps that's another fault condition you don't appear to know can happen.
Then there is the simple upgrade as you state. Serious overload potential if they have done as you stated is OK and fitted a higher current breaker than the cable as you have just stated is perfectly safe. At least if you do the job correctly in the first place, and fit a breaker that's less than the cable capacity, the incorrectly fitted wrong shower will keep tripping the circuit. This should alert the user that something is wrong and is safe other than getting cold showers. Doing as you stated was safe on the other hand will not result in the user noticing as it won't trip, they won't get cold showers. However the cable will heat up and depending on how long the user showers for may melt and do other things. With luck it would just short and trip your over rated breaker, I wouldn't like to rely on that failure mode to ensure safety myself.
Fitting a breaker that is higher than the cables capacity always leads to potentially unsafe conditions being introduced without the user knowing. This applies to 2.5 mm2 spurs and rings no matter what you claim. Their safety comes from a long list of don't do that, don't do that, etc. and we all know people obey all the rules don't we! Even people that don't know what the rules are.
You can continue to follow the minimum the regs say, I don't care, I will not do electrical work to the minimum standard. I know how to make circuits safer and I will continue to do so. It costs peanuts to fit bigger cables and/or smaller breakers to fully protect circuits and that's what I will continue to do. The IEE haven't convinced me that what you claim is safe enough so you have no chance, especially in view of the obvious safety errors you keep making in your posts.
I did not mention it. If you think I did, then provide evidence.
see above
The first case, is probably true, and the second probably false. Rings have overload and fault protection at the origin. Even though connecting a shower to one is highly undesirable for many reasons, the chances are it will not cause any damage to the circuit[1] - as is evidenced by the many bodged installations where this has been done. Generally bad stuff does not happen. (a 32A MDB will happily supply 40A for 10s of minutes, and a pair of 2.5mm^2 T&Es will carry the load without damage if there is not much other load on the circuit).
[1] The normal damage evident is when the connection to the ring is also made in 2.5mm^2 T&E - then that usually overheats quite seriously at the terminations. A connection made in a larger cable will often run for years without notable damage - although the occasional trip of the circuit breaker would not be unexpected.
What did you have in mind?
The only fundamental change to ring specifications I can think of is the upgrading of the CPC to 1.5mm^2 - and that was really a follow on from research into performance of re-wireable fuses.
Having said that, patterns of use and available technology are ever evolving and changing well, so it is only right and proper that the wiring reulations keep track of this. So change in itself is often a good thing.
I was, and you were replying to my comments on them. Short term memory problem?
How do you manage to sound like such a prat in so few words? Is is a natural talent or have you had to practice?
Yes you could get a short in an element, the usual result is either an earth fault which disconnects the power, or a hot spot which rapidly blows the element open circuit, or trips the showers thermal cutout. A significant element resistance reduction that is sustainable for any meaningful time seems rather harder to conceive.
The point of relevance is that even if there is a simple like for like swap, there is *no* "simple" upgrade. If replacing a shower with a higher power one, then the installer must go through the design exercise again, to make sure that it is appropriate.
No, I said it was safe with the original shower. If you go changing stuff, then its your responsibility to ensure it remains safe.
"correctly" as you inappropriately call it, is alas not always an option.
If you have a shower with peak demand of 41A, and cable with a current carrying capacity of 47A as installed, then the ideal MCB size would be
45A.
The reality is that many makers don't do a 45A MCB so the choice is 40 or 50A. In that circumstance you either have to fit the 40A MCB with the knowledge that the design current exceeds its rating, or you fit the
50A, and show by measurement and calculation that it provides fault protection for the cable (which must be provided at the origin of the circuit), with the knowledge that that since the shower has a lower maximum demand than the cable, overload prevention is ensured by the specification of the load.
Obviously if you have the choice of the 45A MCB in the above scenario then you use that, if you don't then you go for the second option or replace the circuit cable with 10mm^2 if possible.
Why would you?
You seem to be back to prattling on about altering circuit parameters without going through the required design process again, and then complaining that something is out of spec.
If you consider yourself competent to upgrade a shower, then you would identify the shortcoming of the supply for the more powerful one and rectify it as a part of the process. Don't whinge if the last installer provided a safe working setup, and by fiddling you broke it.
Always dennis? Prey tell...
Does that 3A flex on your light pendant always result in an unsafe condition without you knowing? The reality is the same logic applies - the MCB provides fault protection for the flex but not overload protection. The design of bulb holder and the available choice of bulbs limits the possibility of overload.
You may believe that, however there is a vast body of practical empirical evidence that suggests otherwise. That you choose to carry on believing it in spite of the evidence says more about you than anything else.
There are few rules, and they are not complex. If you don't understand them, then don't undertake the work.
I have no desire to convince you one way or the other dennis. By all means do what you like in your own home.
As to whether your standard of work is safer or otherwise, we can only take your assertion at face value, and attribute to it the respect it deserves based on your posting history on these matters.
You had better tell the IEE they are wrong about point loads on a ring then. It appears that you can prove its safe to do what they specifically tell you not to do. Think of how many pence you can save.
I thought that I stated they reduced the allowed sockets on spurs, maybe you forgot.
Yes and I changed it to not use a breaker larger than the cable rating, I expect you will catch up sooner or later.
The hell you were, you were talking about connecting showers to lighting circuits. If you think that's a shower circuit I think you have a problem, a big problem and its not just your short term memory.
Well so far you have not been able to prove what I say is wrong. You have however managed to not know how a lighting circuit would behave if you connect a shower to it and have managed to state a point load of 40A is OK on a 2.5 mm2 ring even though the regs tell you its unsafe.
So now you are going to guarantee all failure modes on high powered heaters so they don't break your rules required to make things safe. we have been here before about needing lots of rules to make your idea of a safe circuit safe in use. I still think you are wrong to rely on rules rather than proper protection.
Its the same as your argument that other equipment will fail first ensuring any overload will be cleared before any circuit damage. It requires that nobody actually makes quality equipment that doesn't fail, a very strange way to ensure safety.
What exactly does that have to do with the argument?
That's life. You are talking about shower circuits not what the argument is about.
According to you I could fit a 100 A (no I haven't done the fault condition calcs as they don't matter here) breaker in a 10 mm2 circuit and let the shower limit the load. After all a 40A shower can never take more than 100A and its all perfectly safe from overload.
Back to blaming others I see.
No because I know and use 1.5 mm2 flex.
0.75 mm2 flex is useless.
There is no real investigation into many accidents so I can safely ignore the empirical evidence. They just assume they know what caused the incident.
I will ask a pensioner if she knows what the rules are for using trailing sockets and what they can plug in and use then. I don't expect here to know but it appears you do.
Well the last few posts you have made make me wonder if you actually know anything about electrics.
I thought about replying, but he seems so tied up in knots now attempting to win an argument (not actually sure about what, or with who), that it must be terminally dull for everyone.
He's like dribble but without the charm. (with appologies to dribble!)
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