Thoughts please

[jamie-spark]

ah but. the breaker size is to protect the cable. a fault on the 20a load could start a fire before the 100a trips

Not if reg 434.5.2 and 543.1.3 are met ,it would not

 

[D Skelton]

You bored to-nite Mr Skelton?

Very! lol. I'm stuck in a Cumbrian Premier Inn with nowt on telly and the town is closed. I must say I'm looking forward to the breakfast in't morning though

ah but. the breaker size is to protect the cable. a fault on the 20a load could start a fire before the 100a trips

Read my OP again

how long are the 2.5 branches then ?

I see where you're going with this lol.. 3m and all that. Let's just say they are short enough for voltage drop not to be an issue.

and what sort of loads ?
do they need overload protection ?

Ok, each load is a distribution board with a 20A main switch.

 

[ian.settle1]

Very! lol. I'm stuck in a Cumbrian Premier Inn with nowt on telly and the town is closed. I must say I'm looking forward to the breakfast in't morning though

Not in Barrow in Furness by any chance:nonod::shame::lol:

 

[D Skelton]

Not in Barrow in Furness by any chance:nonod::shame::lol:

No, Kendal. Why do you ask?

 

[ian.settle1]

No, Kendal. Why do you ask?

Went to Barrow once and it was shut thats why I was asking

 

[D Skelton]

Went to Barrow once and it was shut thats why I was asking

Lol, I think the whole of the Lake District shuts after about 8pm!

 

[D Skelton]

Tut tut, I thought I might have been able to spur on some interesting debate

It has been a while

 

[Engineer54]

Ok, so providing the requirements for 't' (434.5.2) and 'S' (543.1.3) are satisfied, what is wrong with this setup?

Assume 230V SP 50Hz
View attachment 17962

You been reading American text books by any chance?? lol!!

If the loads were changed for OCPD's, then technically, depending on any other circuit constraints, it's fine!! All you are doing then, is placing the OCPD at the end of the lower rated change of conductor size instead of at the origin on the change of conductor size. This has always been permissible in certain circumstances. The smaller cables however, will require enhanced mechanical protection, for obvious reasons!! lol!!

 

[D Skelton]

Haha, yes, read on through the thread mate

I should have really specified that the hypothetical 20A loads were either OCPDs or loads that were guaranteed not to exceed 20A as that is what I had in mind.

 

[NickD]

My point is that although not an ideal setup, it is not technically wrong. Or at least I can't see a reason why it is against regs.

2.5mm cable protected by a 100A fuse. 2.5mm could be carrying 90A overload and melting and fuse will do nothing. Fails second 'clause' of correct co-ordination requirement (design current <= fuse current <= cable current capacity), wherever that is in the regs...433.1.1(ii)

 

[D Skelton]

Read my last post Overload is not a factor.

 

[NickD]

Read my last post Overload is not a factor.

That may be so. But thinking purely in terms of compliance with the regs, explain to me how that gets around the categorical requirements of 433.1.1(ii).

 

[NickD]

Read my last post Overload is not a factor.

And explain to me how your 20A OCPDs stop somebody putting a cunningly calibrated (230/90) ohm nail into one of your 2.5mm cables.

 

[NickD]

Premier Inn? Luxury. When I were t'lad we 'ad to stay in't 'ole in t'Travelodge carpark.

 

[D Skelton]

That may be so. But thinking purely in terms of compliance with the regs, explain to me how that gets around the categorical requirements of 433.1.1(ii).

The circuits have been designed to comply with 433.1 therefore 433.1.1 is irrelevant. Also, see 433.2.2 (i).

And explain to me how your 20A OCPDs stop somebody putting a cunningly calibrated (230/90) ohm nail into one of your 2.5mm cables.

What is to stop someone jumping off a train platform and licking a live rail?? Naa, in all seriousness though, find me a two and a half ohm nail and I'll give you a million squids!

Premier Inn? Luxury. When I were t'lad we 'ad to stay in't 'ole in t'Travelodge carpark.

Yeah, I normally do Travelodge but I decided to be posh this time haha!