The purpose of the Safe Isolation procedure is to ensure that a circuit is in a proven de-energised state that is safe to work on, and therefore complying with the statutory requirements of EAWR:1989, Regulation 14a. Which states "No person shall be engaged in any work activity on or near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless - a) it is unreasonable in all circumstances for it to be dead; and b) it is reasonable in all the circumstances for him to be at work on or near it while it is live; and c) suitable precautions (including where necessary the provision of suitable protective equipment) are taken to prevent injury. Such work is permitted only if conditions a) and b) and c) are satisfied, ‘Work’ is not confined to electrical work but includes any work activity.”
HSE, Guidance Note GS38, conveniently paraphrases the salient points of EAWR:1989, Regulation 14a, “No live working unless:- (i) it is unreasonable to work dead; AND (ii) it is reasonable to work live; AND (iii) suitable precautions are taken to prevent injury.
It is my view that if the Safe Isolation procedure is implemented to prove a circuit is “dead”, the electrician has decided and implied that it is unreasonable to work live. If he then checks the operation of his approved voltage tester (AVT) on a known LIVE supply, he is effectively infringing the very regulation he is attempting to comply with.
So, therefore, I believe a proving unit (providing it can test the AVT to full scale) to be the best method of checking the operation of the approved voltage tester, allowing the electrician to satisfy the requirements EAWR:1989, Regulation 14a, without conflict.