BS 7671 makes no distinction between an electrical installation that is permanently fixed to a building structure and one that is not. It defines an electrical installation as “as assembly of associated electrical equipment having coordinated characteristics to fulfill a specific purpose”. It goes on to define a temporary electrical installation as an “electrical installation erected for a particular purpose and dismantled when no longer required for that purpose”. The key point to note is that despite being temporary, in BS 7671 it is still referred to as an ‘installation’.
BS 7909 tries to make a distinction between permanent installations where equipment is permanently bolted to the building structure and temporary electrical distributions.
Throughout the course of the lifetime of the temporary system it should perform effectively and safely. A Christmas lighting display would have a defined period of existence whereas a theatre show may have a planned run extended if it proves successful at the box office. There is no time limit that a temporary system may stay in existence but BS 7909 requires that the designer takes into account all the factors likely to affect the system for its original planned duration, with a date stated on the Completion Certificate at which a further assessment should be made to ensure the continued adequacy of the system. So a designer of a system used for a TV drama that is due to run for six weeks may state a reassessment date of eight weeks to allow for minor overrun, but give an indication that a proper review should be taken of the system if it is proving to be a popular show and the run is being extended accordingly.