2 circuits in 4 core swa?

[solo2771]

Just a quicky,
Lighting circuit supplied by 4 core swa has become overloaded.
Would there be anything wrong with splitting into 2 circuits and using the 4 cores for L and N and the steel armour for earth for both? all conductors would be identified with sleeving.
Otherwise new cable needs running under concrete.

 

[scotsparky]

you would have to be absolutly positive the SWA of the cable would mannage the simultanious fault current on both circuits. It would involve a lot of cals and as it is probbably a smallish cable i seriously dought it would.
I dont think it can be done so get the cutter out and start digging sorry

 

[acat]

Agree with the above and have a read of 514.4.4 and table 51 no mention of sleeving being permitted for identification of conductors.


Chris

 

[scotsparky]

acat have a gander at 514.3.2

 

[just add water sparks]

would not taking Zs values give some indication ????? just throwing ideas in pot not necessarily saying its correct

 

[andyb]

I don't think that there's a problem with several circuits sharing an earth provided the csa is rated for the largest circuit.
You would need to know the equivalent csa of the armoured.

 

[scotsparky]

you would have to work out worst case and make sure on a similtanious earth fault on both circuits the swa would take it.
Manufacturest details for SWA Kfactor from section 5 etc

 

[andyb]

According to 543.1.2 where a protective conductor is common to two or more circuits it's csa shall be calculated for the most onerous fault current and operating time in each circuit, or selected so as to correspond to the csa of the largest line conductor.

 

[solo2771]

DEcided to get them to get the breakers out as they use them anyway and just putting another swa in, thankyou for answers and it is something I am going to look into at some point. My main concern with using armourings is on jobs I have repaired in past water has got into the armourings and they have rusted almost away even though they had decent external gland kits fitted.

 

[1billy wiz]

cant the neutral be hALf the size of the line or is that only for 3 phase??

 

[scotsparky]

billy In a true ballanced 3 phase no no need for a neutral at all anywhere else the Neutral is classes as a line conductor therefore has to be the same as all aother line conductor.

Reg 534.2