3rd party certification to one side, there should be a system in place to officially resolve such situations. Electricians pass away, companies go under or are in dispute, i.e. there is a good reason why the original installer cannot finish or sign the certificate.
In the south of Ireland there is a procedure in place to deal with precisely these types of issues so that a DSO supply can be obtained.
This is the Change of Contractor procedure. The person responsible for the installation applies for a Change of Contractor to RECI with the details of the installing contractor and the new contractor. If the details of the installing contractor are filled in as "unknown" then the Report Illegal Works procedure is automatically invoked.
RECI will contact the original contractor to establish why the job has not been completed/certified, and will then authorise the new contractor to complete and certify the installation. Only after written permission has been received can works begin.
The new contractor will complete the job, carry out Pre-Connection Tests and send an Inspection Request form to RECI. RECI will then send out one of their Inspectors to carry out initial verification again with the Registered Electrical Contractor (REC), and compare results to the Test Record Sheet.
If there are non-compliances then an additional Inspection will be mandated. Each of these Inspections will cost €250 (in addition to the contractor's time).
Once RECI are happy they will authorise the new contractor to submit a Completion Certificate for the job. Once the job has been energised by the DSO (ESB) then the contractor will return to carry out Post-Connection Tests.
It is a serious disciplinary offence (which can result in dismissal/de-registration) to certify anyone else's job without specific written authority from RECI.