7.12.2 Requirements for alternative sources of supply

• 7.12.2.1 Where any form of alternative supply (emergency supply, UPS etc.), is connected to an electrical installation, a notice to this effect shall be displayed at the main switch of the installation, and where such supply
  a) supplies power only to certain circuits in a distribution board, a power-on indicator (visible or audible) shall be provided on each such distribution board as well as a notice indicating that the standby power main switch shall also be switched off in an emergency,
  b) only supplies a part of the electrical installation, the notice shall also be displayed on each distribution board in that part of the installation (see 6.6.1.1(d)).
   
• 7.12.2.2 The means of excitation and commutation shall be appropriate for the intended use of the generating set and the safety and proper functioning of other sources of supply shall not be impaired by the generating plant.
   
• 7.12.2.3 The prospective short-circuit current and prospective earth fault current shall be assessed for each source of supply or combination of sources, which can operate independently of other sources or combinations. The short-circuit rating of protective devices within the installation and, where appropriate, connected to the main supply, shall not be exceeded for any of the intended methods of operation of the sources.
   
• 7.12.2.4 Where the alternative supply is intended to provide a supply to an installation that is not connected to the main supply, or to provide a supply as a switched alternative to the main supply, the capacity and operating characteristics of the alternative supply shall be such that danger or damage to equipment does not arise after the connection or disconnection of any intended load as a result of the deviation of the voltage or frequency from the standard range. Means shall be provided to automatically disconnect such parts of the installation, as may be necessary if the capacity of the alternative supply is exceeded.
   
• 7.12.2.5 Where an alternative supply is provided to an installation or part of an installation as a switched alternative to the main supply, the change-over switching device shall disconnect the main supply before the alternative supply is switched in. The change-over switching device shall be interlocked in such a way that the main supply and the alternative supply cannot be connected to the installation or part of the installation at the same time.
   
• 7.12.2.6 Except where otherwise permitted in this part of SANS 10142, where a socket-outlet is installed in a circuit on standby power, such circuit shall be protected by an earth leakage protection device with a rated earth leakage tripping current (rated residual current) I∆n not exceeding 30 mA.
   
• 7.12.2.7 A 230 V generator with a V-O-V earth connection (centre tap on winding which is earthed), shall not be connected to a fixed electrical installation.

ALL ratings are approximate and at SEA LEVEL. Engines need to be de-rated for altitude. A rough guide to de-rate performance is 1% for every 100m above sea level. I.e: A 20kVA at sea level is an 18kVA at 1000m above sea level (10% less) etc.