Joining z MV 3c, Cu screened cable with SWA to a MV 3c, Cu screened cable without SWA

[EddyWirbelstrom]

A damaged section of an existing cable is to be removed and replaced with a new cable.
- Existing Cable: 3c, Al, XLPE/Cu screen on each core/PVC, 3.8/6.6kV
- New Cable: 3c, Al, XLPE/Cu screen on each core/SWA/PVC , 3.8/6.6kV
Two cable joins are required.
Continuity of the copper screens of each conductor will be affected by connecting each screen of the existing cable conductor to the screen of the corresponding conductor of the new cable.
At each terminating end of the existing cable, the screens of the three phase conductors will be solidly bonded and connected to earth.
At the two joints between the new cable and the existing cable, the steel wire armouring ( SWA ) of the new cable will be connected to earth electrodes.
The existing cable does not have SWA.

Question:
Should the SWA of the new cable be bonded to the screens of the existing and new conductor ?
How do MV cable joints accommodate connecting a 3c, Al, XLPE/Cu Screen on each core/PVC cable without SWA with a cable with SWA ?

 

[Kiribanda]

I believe that these cables are designed, manufactured and tested for BS6622/ IEC60502.
Therefore, the SWA of the cable is just for mechanical protection. That means, if the SWA is
supposed to take the earth fault current then it should be designed/ tested for that current which
is not normal always.
On the other hand the metallic screen of a cable is designed to take the earth fault current
and the cable data sheet shows the amount of current designed/ tested.
Therefore,
1) The SWA of the new cable piece should not be bonded to the screens. The SWA can be separately earthed at the termination point of the cable.
2) At the joint you have to BOND the two screens solidly and allow the the SCREEN to continue up to the end of the cable and
all the three screens are taken out at the termination and bonded to the same common earthing point at the termination point.

 

[EddyWirbelstrom]

Thank you Kiribanda for your very helpful reply.
I will ensure that the max/min PPP and PPE short-circuit currents do not exceed the short-time withstand ratings of the conductor and screen respectively.