I should have been a little more precise. What I want to do is remove the need for external earthing and use a triple with one of the cores being the bonding conductor. The screen/armour is on earthed at the control end, the device is also connected to pipework (which is earthed) and sometime a bracket (that is connected to the main skid). Lookind at all the EMC and bonding IEC's I cannot find anything that prevents this, although a BP specification states that usually both ends of a 'spare' core will not be earthed at each end. Shell and total are prety similar.
Your help is once again appreciated.