All of the plumbing to the bathroom in my house is plastic for the sink, bath, toilet and radiators, although some of the pipework within the bathroom is in copper (radiator tails and some of the interconnections between the bath, toilet and sink). I am looking to having an electric shower fitted, and have been told that no supplimentary bonding will be required, and that just the protective conductor in the wiring to the shower unit will suffice. Is this correct?