Transformer incomer Pothead

[Electrometrical]

We have a 13.8kV/4160V, 20MVA transformer. Incomer is connected to transformer through a pothead (a HV side cable junction box). Incoming cable is 400mm2 (PILC). Inside the box, the cable is insulated with Raychem 15KV rated heat shrink sleeves. My question is that after having heat shrink sleeves, do we need to fill the box with a filler compound (e.g. Novoid X)?

 

[Marmite]

It depends on the phase-phase and phase to earth clearances available in the box to achieve the system BIL.
Regards
Marmite

 

[Electrometrical]

Thanks. Do you any idea what would be phase to phase clearance as per CSA?

Moreover, at what clearance level (P-P) or (P-E), we would need an additional filler (like Novoid X)?