Every submersible bore pump should "hang" on the metric poly pipe and not on the stainless steel safety cable or the electrical cable.   Stainless steel safety cable is required to provide insurance for those unfortunate times when the metric poly pipe breaks or loosens in the fittings.   This does not happen often but, if it does, you want to be able to retrieve your pump from down the hole so stainless steel safety cable is definitely required.   Our 3mm stainless steel safety cable is made from 316L stainless steel.