The main switch can not be overloaded as the main cut out fuse will prevent it.
Too many circuits?
- Thread starter veedee
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Definitely not familiar with it
Is that a similar kind of cable to the DNO feed that comes into the home? In what scenarios would it be used to feed a consumer unit rather than a set of "standard" tails?
It is the same cable the DNO would use for a TN-S supply.
This consumer unit is about a 20 metre run from the cutout, so can not be fed straight from the incommer without overcurrent protection.
Hmmmmm
Are you suggesting that, by analogy with the 'tabulated CCCs' of cables, the 'current rating' of a main switch (or any other component/accessory) takes into account the characteristics of OPDs?
If we had a cable with a tabulated CCC of 100A, that would mean that it was deemed that it would come to no harm with 145A flowing for at least 1 hour. Are you suggesting that, similarly, a main switch 'rated' at "100A" is deemed to be safe to carry 145A for at least an hour - and, perhaps more relevant in the case of a switch, that it could safely break a current of at least 145A?
Kind Regards, John
That, in itself, does not explain why it is split-con, does it?
Kind Regards, John
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Hmmmmm
Are you suggesting that, by analogy with the 'tabulated CCCs' of cables, the 'current rating' of a main switch (or any other component/accessory) takes into account the characteristics of OPDs?
If we had a cable with a tabulated CCC of 100A, that would mean that it was deemed that it would come to no harm with 145A flowing for at least 1 hour. Are you suggesting that, similarly, a main switch 'rated' at "100A" is deemed to be safe to carry 145A for at least an hour - and, perhaps more relevant in the case of a switch, that it could safely break a current of at least 145A?
Kind Regards, John
You’re using unicorns to try and prove yourself superior to the regulations again. I will not comment further on this as it’s pointless and just encourages you.
To run a 25mm² you’ve basically got 4 choices.
1, single cores (meter tails and earth)
2, SWA
3, split con
4, some other less common cable such as YY
Split con is cheaper, smaller, neater, easier to install and has more mechanical strength than tails. It’s easier to terminate than SWA and doesn’t require specific glands etc.
You misunderstand. I'm not trying to 'be clever' but, rather, am trying to learn, because you have suggested/implied a concept I had not come across before.
I have always thought/believed that if a component such as a switch has a 'rating' of, say, 100A, that means that it cannot be assumed to be safe at a current >100A (which would be regarded as 'an overload', of the switch/whatever). If that were the case, then if one wanted to "protect it from 'overload' " with a fuse (which is what you suggested the cutout fuse would do), one would need a fuse rated at considerably less than 100A (somewhat under 70A, if one wanted to avoid >100A through switch for an hour).
So, am I wrong in my belief that if one wants to 'protect a 100A switch from overload', one has to do something which would prevent >100A flowing for an appreciable time?
Kind Regards, John
Fair enough - that makes sense. The distribution circuits in my house all use 16mm² or 25mm² singles, but I suppose that split con would have been a reasonable, maybe preferable, alterative.
Kind Regards, John
One comment: it’s easier to make a tidy job if there is plenty of space. RCBOs take up more space than MCBs. If I were you, I’d get a significantly larger enclosure than you need for the circuits.
(I write this having spent the afternoon adding a new circuit for mains-powered smoke alarms to my CU, which was “professionally” installed by a spotty teenage apprentice a couple of years ago. To be fair to the guy he was somewhat limited by the lack of slack on the existing wiring, but the result is a rat’s nest.)
Why didn't you add it to the lighting circuit?
Andy
Andy
Well, that was another option but I think I would still have needed to make the connection inside the CU; the lighting wiring is all in conduit and thoroughly buried in walls and ceilings.
Quite a lot of manufacturers are now offering compact RCBOs which are not much bigger than a circuit breaker.
These are Hager flavoured ones.
Circuit Breaker, Compact RCBO, standard RCBO
On reflection, maybe it is just me having had a life-long misunderstanding, since it's "not just you". Whilst you wrote:
... this started because flameport wrote:
Hence, both of you are saying that, say, an upstream 60A fuse would be adequate to protect an RCD or main switch 'rated' at 63A (and flameport is also saying that downstream OPDs with Ins totalling no more than 63A would also offer adequate protection), in all cases despite the fact that the fuse/MCBs would allow a lot more than 63A to flow through the device for an appreciable period.
Do I therefore take it that you both are saying that it is OK to use a device 'rated at' X amps, so long as there are OPDs either upstream or downstream of it which have an In (or total In) of ≤X amps, even though such OPDs will allow a lot more than X amps to flow through the device for an appreciable time?
... and, again, let me repeat that I am not 'trying to be clever' or argumentative. I want to learn, because it seems that I may always have had a misunderstanding about this.
Kind Regards, John
???
The neutral fly lead 'supplied' connects to the neutral terminal in the board.
It's not 'two outputs', more of a sensing wire.
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