adiabatic and what to do

[Spark123]

You either have to comply with table 54.7 or the adiabatic equation.
The CPC in SWA for XPLE 10mm 2C does not comply with table 54.7 however it will almost certainly comply with the adiabatic.
Same way that we get away with a reduced CPC in twin and earth - they don't comply with table 54.7 but they will pass the adiabatic.

 

[BSBS]

What I'm getting at is that if the SWA does not meet the requirements of a CPC, then the SWA cable no longer complies with the reg that says "earthed metallic covering suitable for use as a CPC", and thus, that type of SWA cable is useless. Even if you use a core or an external CPC, the metallic covering still ain't suitable for use as a CPC.

Seems daft.

I can see what you are getting at, however I think you may be taking it to literally. The SWA is suitable to be used as a CPC however in some circumstances a particular size of cable the SWA may not meet the size requirments for a given circuit. This would not mean that the SWA was not suitable to be used in general as its construction is an earthed metalic covering. Take SY Cable, in certain sizes of cable the braiding may meet CPC requirements (im not saying it actually will just using it as an example) but the construction of SY makes it unsuitable to be used as an earthed metalic covering. The same can be said for trunking, It is suitable to be used as a CPC but some sizes may not be suitable depending on requirements for the circuits it contains.

 

[ricicle]

The point being that although you may overcome the undersized armour by using an inner core or seperate cpc, you still need the protective device to operate in the correct time if the swa was penetrated at the extremity of the cable and the armour needs to be able to carry the fault current without detrement to the cable

 

[17thman]

Hi guys

Thanks for the link Garymo

Thanks for all your interesting help and input all.

With an Earth fault current of 904A and a disconnection time of 1.3s for the fuse type and k is 51 from 54.4. The adiabatic gives 20mm2.

From the link Garymo gave, then the csa of 2 core swa is 41mm2, so i assume it is ok to proceed with the current arrangement.

Any disagreements would be listened to..Thanks