Spur from cooker supply

[timhoward]

The change in cable size got me thinking.

So the general rule is that the current carrying capacity of the cable will exceed the protective device (32 amps) in
normal cases. 6 sq mm will normally carry 32 amps. 2.5 sq mm won't.
So the correct alarm bell went off.

We're therefore looking for exceptions to this rule.
I've believed (and maybe I'm about to be shot down myself!) that the reg I posted above regarding overload protection, and the similar one for fault protection could be applied to the situation where there's a cable that no-one can get to, if adequately secured, and there was a further protective device within 3m.

 

[Callumh1992]

So the general rule is that the current carrying capacity of the cable will exceed the protective device (32 amps) in
normal cases. 6 sq mm will normally carry 32 amps. 2.5 sq mm won't.
So the correct alarm bell went off.

We're therefore looking for exceptions to this rule.
I've believed (and maybe I'm about to be shot down myself!) that the reg I posted above regarding overload protection, and the similar one for fault protection could be applied to the situation where there's a cable that no-one can get to, if adequately secured, and there was a further protective device within 3m.

Ok so the cable is clipped to the posts running about 1.5m from the cooker switch down to the 13a switched socket. I’m assuming the 13a plug top counts and a protective device or would I change to a spur?

 

[James]

So the general rule is that the current carrying capacity of the cable will exceed the protective device (32 amps) in
normal cases. 6 sq mm will normally carry 32 amps. 2.5 sq mm won't.
So the correct alarm bell went off.

We're therefore looking for exceptions to this rule.
I've believed (and maybe I'm about to be shot down myself!) that the reg I posted above regarding overload protection, and the similar one for fault protection could be applied to the situation where there's a cable that no-one can get to, if adequately secured, and there was a further protective device within 3m.

I agree, if it was not possible to feed a socket from 2.5mm (single run) from a circuit spurred off or joined to a 32A distribution circuit or similar then 90% of homes and businesses would fail on that point.

lets face it, a spur from a ring has similar protective devices and a single 6mm cable is similar to 2 x 2.5mm run in a ring or parallel.
overload is obviously sorted by the fuse in the plug so we are only looking at fault protection anyway.

 

[James]

There is a huge difference between

comparing an instalation to what is considered best practice and trying to figure out how to code things that dont match up

to

understanding the science behind the regs and applying them with a level head to ensure the installation is actually safe, ensuring that failures are noted correctly.

 

[Pretty Mouth]

I would put this down to 433.3.1(ii) - no overload protection needed because the load at the single socket can't overload the cable, being fused at 13A. The 32A protective device should deal with fault current.

But actually, this arrangement is shown in appendix 15, figure 15B on p556 - a 4mm radial on a 32A, with a twin socket spurred in 2.5mm. If diversity says it's okay (which in my experience it usually does) then all good

I’m hopeless with regs.

They're not easy reading it has to be said, but persevere, you'll get to understand them better if you keep at it. I recommend reading chapter 43 - protection against overcurrent on p92. It's only about 8 pages long and covers this subject. Just ask if you have trouble understanding, we'll help you out. Also appendix 15 p555.