Pre-commissioning and dead testing

How does Pre-commissioning and dead testing work, step by step?

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   Step 1: Define what mechanical completion means

   Completion is defined in writing before anyone claims it: what must be installed, what must be inspected, what must be documented, and what may be outstanding. Without that definition, completion becomes a matter of opinion and the argument happens at the worst possible moment. The definition is agreed between the contractor, the client's representative and the commissioning team at the start of the works, not at the end.

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   Step 2: Verify the installation against the design

   Every position is checked: correct equipment, correct location, correct orientation, correct fixings, correct earthing, correct labelling. Discrepancies are logged and either corrected or accepted through a formal process with the designer. On a repetitive site this is done by working through a schedule rather than by walking round looking, because the items that get missed are always the ones nobody was specifically looking for.

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   Step 3: Verify the cabling and terminations

   Cables are checked for correct identification, correct routing, correct termination and correct labelling at both ends, and the cable schedule is reconciled with what is actually installed. On a large battery site this is a substantial exercise in its own right. It is also the single most productive one, because incorrect terminations are both the most common installation defect and the most disruptive to discover later.

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   Step 4: Carry out the dead tests

   The tests that can be carried out with the system unenergised are performed by competent parties to the specification, and the results are recorded. What is tested, how, and what constitutes a pass are set by the electrical designer and the specification for the project. Results are reviewed as they are produced rather than filed, because a pattern across several results usually means something different from a single failure.

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   Step 5: Prove the control and communications system dead

   As much of the control system as can be proved without the power system being live is proved: communications paths, addressing, signal identification, alarm routing and the interfaces between the control system and each item of equipment. Control problems are the most common cause of delay during energisation, and most of them can be found and fixed while the site is still safely dead.

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   Step 6: Confirm the safety and fire arrangements are in place

   Before the site can move towards energisation, the fire strategy provisions have to be in place and evidenced: layout and separation as designed, barriers built and inspected, detection and ventilation arrangements installed and proved as the fire engineer requires, and water, access and containment complete and tested. The site is about to stop being a construction site, and these provisions are part of what makes that acceptable.

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   Step 7: Assemble the documentation pack

   The evidence is assembled as a coherent pack rather than a box of paperwork: inspection records, test results, as-built drawings, cable schedules, equipment certification, fire strategy evidence and the outstanding items list. The pack is what the authorisation to proceed is granted against, and the network operator will look at parts of it. Assembling it at the end, from memory, is how projects lose weeks.

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   Step 8: Hold the site and obtain authorisation to proceed

   With pre-commissioning complete the installation is held in a defined, unenergised, secured state, and authorisation to move to the next stage is sought through the process set out for the project. Access to the installation from this point is controlled by the commissioning organisation rather than by the construction team. That change of control is the real boundary between building the site and commissioning it.