Wha????? Electrical tape is not self amalgamating, and self amalgamating tape (rescue tape / rigging tape) is not Butyl rubber/tape. So color me confused cuz I have no idea what you mean?
In that case you're obviously not an electrician :-)
Try googling self-amalgamating tape, which is butyl tape we use in the electrical industry to re-insulate stuff. PVC electrical tape is what you are thinking of.