I would say when you get beneficial use from the equipment. What does the supplier say with regards to warranty periods?

FB You need to ask who will "own" the plant while the your product is being produced. Whose insurance company will underwrite the risk of injury to your personnel, damage to the machinery and to your product when your employees are using the supplier's machinery, which has not been signed over and which, as you say, is not yet legal? Who will cover the risk to the commissioning crew when working on already-producing machinery? Will your employers' liability insurance company cover the risk to your employees when they are using non-certified and illegal machinery and will your managers be willing to accept the potential corporate manslaughter implications of their decision? What permit-to-work control will be in place and who will perform the risk assessment and produce the operations manual and who will train your operators and to what standard? The supplier's insurance company will almost certainly wash their hands of any damage to the plant caused by your employees using it before it has been certified (CE mark, declaration of conformity and operational instructions etc.) and formally handed over to you. Who, too, will cover the product liability aspects of the "on hold" product when it is finally released to the market and which can (must) be identified by serial number or batch number? There are many examples of companies not having to pay for accidental damage caused to equipment when it was still under the control of the commissioning crew and in addition, being able to win damages for the lost production which followed. Your situation can best be described as a can of worms. Having just read your statement that the machinery has been purchased outside the EU, you will need to identify who will sign the declaration of conformity and confirm compliance with all the other aspects of PUWER and the supply of machinery (safety) regulations. Kind regards, Chris

In the wider context it isn't unusual to operate whilst snagging issues are to be resolved and (dare I say it) the situation can be a dynamic one. In your specific context, I'd expect someone to be signing-off on the essential safety (i.e. CE) elements before any sort of production. Anything less is contrary to PUWER and the potential for interlock or othe safety feature failure is, from your perspective, unquantifiable. The powers that be may be content to take that risk, and presumably the potential consequences, but the operators are caught in the middle of things and the group likely to sustain serious injury if things go awry.