does this comply?

[Andy™]

i peronally dont agree with that one as with a ring mains installed the zs is lower than having a radial as there are 2 earth cables for the current to flow through not 1 earth for the current to flow through, please no jokes about sultanas :^O

the only good advantage of a ring over radial is much harder to loose an earth

 

[Badger]

well that as well, but the zs is still lower

 

[sparkytim]

But now with RCD protection on most Rings and Radials, low Zs not much of an important factor.

 

[Lee321]

But now with RCD protection on most Rings and Radials, low Zs not much of an important factor.

get in.back of the net tim

 

[Nicky Tesla]

We are compliant due to reg 433.1.5

this is the bit your missing ian

"and if, under the intended conditions of use, the load current in ANY part of the cct is unlikely to exceed FOR LONG PERIODS the CURRENT CARRYING CAPACITY OF THE CABLE"

From a spur, under intended use, that cable feeding the spur, will not exceed for long periods, the current carrying capacity of the cable....ie exactly the same as for a radial which it is anyway.

Apart from the above, the reg is not relevant to the situation. headbang

 

[green-hornet]

Would like to know how the circuit would behave if the fuse went at 10pm, and the kitchen foil was used to wrap the fuse?

 

[Lee321]

Would like to know how the circuit would behave if the fuse went at 10pm, and the kitchen foil was used to wrap the fuse?

well if the appliance decided to pull a current far inexcess of the 13a lets say

27? the 2.5 would still be ok but the flex won't ROTFWL

same as if it was a ring the flex would be exposed to 32a possibly

assuming the foil was indestructable

 

[ADS]

Okay, we don't like rings:O

So, just to throw a spanner in the works:

If we swap the 2.5mm radial that is feeding the FCU, for a 4mm radial, does the circuit now comply?

So the scenario is now a 4mm cable feeding a FCU and a 2.5mm cable feeding a double socket outlet, both from a 32A RCBO.

Basically, a 4mm radial with a 2.5mm unfused spur

Appendix 15

(4mm Radial Circuit)

Unfused spur

An unfused spur run in 2.5 mm2 cable should feed one single or one twin socket-outlet only.

An unfused spur may be connected to the origin of the circuit in the distribution board

If the answer is yes, it does now comply, what's changed (with regards overload protection) for the 2.5mm cable feeding the socket outlets - compared with the ops original scenario?

 

[green-hornet]

Do you know, I was adamant that this would not comply but now ?

Well I think we can all say that from a design point of view we would not do it.

Given other posts and the latest from ADS I have to say that whilst I was sure it was against the regulations I find no argument against it.

I have to hold my hand up and admit I was wrong.

Learn something everyday.

 

[ianmacd]

That is still a bit of a grey area as if you follow the example in the appendix with 4mm radial then, yes, it now complies, but they do not seem to back it up with a reg number that allows it. Has anyone found one? They do one for rings why not for 4mm radials?

There are 2 things to point out here too:

1) Its electrically no different but the regs (potentially) allow for this scenario, therefore it (potentially) complies when it did not run in all 2.5mm. Stupid, I know but they are the regs.

2) As pointed out by most people, the OP's example would not normally be practised.

IMHO when you install a new circuit, there should be no need to have spurs. Spurs should be left for later modifications. I look forward to a time when both Rings and Spurs are no longer part of the regs.

 

[Andy™]

IMHO when you install a new circuit, there should be no need to have spurs. Spurs should be left for later modifications. I look forward to a time when both Rings and Spurs are no longer part of the regs.

i do sometimes install spurs in a new install - but only if its a FCU next to a double socket. much easier to have 3 cables in the socket than the spur

 

[skillyd]

32A RCBO feeding two 2.5mm cables with a switched fused spur or single socket on the end. So one point per cable. I think yes, but i was told different today and i think they are wrong.

No this does not comply with the regulations as a 2.5mm cable can not carry 32A. The easiest solution is to link the two ends of the radials making the circuit into a 32A Ring final circuit. Failing that you could change the rcbo to a 20A which would comply.

 

[Andy™]

No this does not comply with the regulations as a 2.5mm cable can not carry 32A. The easiest solution is to link the two ends of the radials making the circuit into a 32A Ring final circuit. Failing that you could change the rcbo to a 20A which would comply.

how about reading the thread first.

and i assume you have never added a spur to a ring main either

 

[ianmacd]

[quote name='Andy

 

[Lee321]

come on ian it was obvious skilly had jumped in without taking the whole context on board

 

[ianmacd]

[quote name='Lee

 

[Lee321]

I know but it did beem a little confrontational to a new member.

good call. our shoulders a little forumite wider some how :Salute

:Welcome: skilly

 

[batty]

[quote name='Andy

 

[Nicky Tesla]

ive said before, it only complies if the cable can withstand a fault current which needs confirmation with adiabatic equation. You also need to know the pfc . the Zs and Ze.

Where we take the pfc i am not sure, normally you would do it at the cable end, but i dont understand that cos who knows where the fault will occur.

Eg we may find that a 2.5 radial done in singles with the same size cpc in conduit complies, but 2.5 t&e doesnot. Who knows until the equations are done. Come on lets get this done. ray

 

[Riggy]

You cannot blame him for not wanting to read over 300 posts. Some of these threads are getting ridiculous.

I beg to differ.

1. If he'd read the thread he would have seen the answer he was giving (or similar) on several occasions.

2. This is the most interesting thread that's been on the forum for months in my opinion.