Understanding fused spur

[JohnW2]

I didn't say they did insist on anything; I said why do they not insist on 4mm² for the spur?

I know, but in addition to not insisting that an unfused spur cannot supply two single sockets, it currently doesn't insist on anything, other than that the cable should be at least 2.5 mm² (or 1.5mm² MICC) and have a CCC of at least 20A.

 

[ebee]

So we could add to the normative that a 4.0mm could be used for two single sockets I suppose.

 

[pete01]

So we could add to the normative that a 4.0mm could be used for two single sockets I suppose.

Or two twins?

 

[EFLImpudence]

Or six.



You are all missing the point.

There is no reason to have 'guidance' stating that only one single socket should be on a spur but, as they do state that, it would be a better 'guide' to state that 4mm² should be used for spurs.

 

[ebee]

Well a 2.5 spur on a 2.5 Ring final is OK therefore allowed, needn`t be any bigger csa but you could if you like, no problem.
the one twin or one single was possibly done to prevent the previously allowed two singles being changed to two twins sometime in the future by someone unaware of all but the most basic rules so the rules were tightened up a bit to reduce chances of this happening , well that explanation sounds plausible.
Sometimes simple rules without all the caveats are mucgh easier to follow so they were dumbed down to assist the masses? who knows? could be. KISS is a rule that might be best applied to some rules

 

[EFLImpudence]

Still missing the point.

 

[ebee]

Goon EFLI what point am I missing?

 

[EFLImpudence]

Or six.



You are all missing the point.

There is no reason to have 'guidance' stating that only one single socket should be on a spur but, as they do state that, it would be a better 'guide' to state that 4mm² should be used for spurs.

 

[EFLImpudence]

Goon EFLI

Don't be rude.

 

[JohnW2]

You are all missing the point. .... There is no reason to have 'guidance' stating that only one single socket should be on a spur but, as they do state that, it would be a better 'guide' to state that 4mm² should be used for spurs.

I'mnot sure that there's a lot to be gained by discussing 'what could have been' (but isn't).

I suppose one could equally argue that if they stated that a 32A ring had to be wired in 4mm cable, that would remove the need for some of the reg and a lot of the 'guidance' text in App 15, and would put paid to the repeated discussions about large loads, particularly when close to one end of a ring. There would then be no real point (other than CPC redundancy) in having a ring but, as we know, the regs do not necessarily make sense!

 

[securespark]

Are you talking about the cable 'shrivelling up'? If so, I'm more than a little surprised ...

... even if the 9.5 kW is quoted for 230V (unlikely) that only represents 41.3 A and, as I recently wrote, Method C 2.5mm² cable is deemed to be able to carry 39.15 A for an hour without coming to any harm - and, even in the presence of teenage daughters, showers rarely last for an hour

This was after a year and it was at the switch that the cable deteriorated. Each leg was melted for around 30cm back.

 

[securespark]

Oh and yes, it was a family of 8 with 5 teenage kids.

 

[JohnW2]

This was after a year and it was at the switch that the cable deteriorated. Each leg was melted for around 30cm back.

If the problem were due to the cable having been 'overloaded' it presumably would have affected the entire length of the cable. If the cable was only damaged close to the switch, that presumably was due to poor/loose connections to the switch - something which seems pretty common with 'shower isolators'.

What do you mean by 'each leg' - both the supply and load side of the switch, perhaps?

 

[ebee]

Don't be rude.

apologies it was a typo, it was meant as go on but I bet you realised that

 

[ebee]

I'mnot sure that there's a lot to be gained by discussing 'what could have been' (but isn't).

I suppose one could equally argue that if they stated that a 32A ring had to be wired in 4mm cable, that would remove the need for some of the reg and a lot of the 'guidance' text in App 15, and would put paid to the repeated discussions about large loads, particularly when close to one end of a ring. There would then be no real point (other than CPC redundancy) in having a ring but, as we know, the regs do not necessarily make sense!

Well I could go with that BUT I almost never ever used 4mm T & E for many years of my working life (mostly on domestics) because I had plenty in stock of "common" sizes pertinent to what I actually need.
1/ When rewireable fuses were pretty much the norm.
2/ When MCBs started to become common and the became sort of de-facto.
So. 1.0/2.5/6.0 would suffice for lighting (1.5 usually not required), 2.5 for Rings and radials so 4.0 not required, 6.0 cookers and showers. Later on 10.0 might become more normal for electric showers but not cookers and although cookers could be ok on 4.0 most just carried on with 6.0 (4.0 was usually not much cheaper if at all anyway.
So those three sizes were the mainstay of T & E for most jobs and of course 1.0 3 core & E too.
Flexes were bought by the roll and only replace nearing the end of the roll.
Simple.
PS - earthwire for Main bonding was 6.0 for a long while until PME started to creep in then later became prevalent.
It was predominantly TNS with perhaps quite rarely TT anyway in which case a 6.0 or 10.0 earthwire was OK for an Earth rod or three if more than one Earth rod required then at least one earthrod distance apart but usually two rod lengths of possible, wired as radials each to the earth block or in a ring just for a bit of resilience (Well the main Earth could be considered the most important feature!).
4.0 earthwire for supp bonding (but also used to get an E onto a circuit with no E (Lighting usually) on a very few instances.