Alternative Power Supplies

By now you would already be aware that the SANS 10142 document was updated in 2020. However, are you aware of the addition of an alternative supplies section for systems such as photovoltaic (PV) installations or gas generators? These are systems that one may use, at either their place of residence or business, to save on energy costs or in the event of a power-loss.

In Part 1 of this NEW series, we unpack the requirements and standards of alternative power supplies as per SANS 10142-1:2020.

Alternative supplies include, but are not limited to, low-voltage generating sets, photovoltaic installations, gas generators, diesel generators, wind turbines or a hydropower plant. We start by taking a closer look at the specific criteria for these systems…

Requirements for an Alternative Supply System

  1. It is a requirement that for any form of alternative supply that is connected to an electrical installation, that a notice be displayed at the main switch of the installation. It is also required that:
  1. Supplies power to certain circuits in a distribution board should have a power-on indicator installed on each distribution board, along with a notice that states the standby power main switch shall be switched off in the case of an emergency.
  2. A notice should be displayed on each distribution board stating the alternative power supply is powering that part of the installation.
     
  1. Both the short circuit current and the earth fault current should be assessed for each source of supply, or a combination of the sources. These sources can operate independently of other sources or combinations. The short circuit rating for protective devices should not be exceeded for any method of operation.
  1. If the alternative supply is used to provide power to a system that is not connected to the main supply, then the capacity and the operating characteristics of the alternative supply should not cause any danger or damage to the equipment because of the connection or disconnection of any load. Disconnection of the installation must occur automatically if the capacity of the alternative supply is exceeded.
  1. A change-over switching device is required if the alternative supply of an installation is a switched alternative to the main supply. The changeover switch must disconnect the main supply before switching on the alternative supply. Moreover, the switch must be interlocked in such a way that the main supply and the alternative supply cannot be connected to the installation, or any part of it, at the same time.
  1. A socket outlet that is installed in a circuit on standby power must be protected by an earth leakage protection device with a rated earth leakage tripping current not exceeding 30 mA. This is applicable to all installations except where otherwise permitted in SANS 10142.
  1. A 230V generator that has a V-O-V (centre tap on winding which is earthed) earth connection must not be connected to the fixed electrical installation. This generator can be used as a free-standing unit, but used to provide power to specific appliances.
  1. As an inverter is a device that is required to be fastened or otherwise secured to a fixed location, and would require the use of tools to be moved to another location, it is considered as a fixed appliance. This will require the device to be installed according to the guidelines set by Section 6.16: Fixed Appliances of SANS 10142-1:2020.
     

Earthing Requirements and Earth Leakage Protection - Neutral Bar Earthing

The protection should be provided for an electrical installation in such a way that it ensures the correct operation of the protective devices, irrespective of the power source. These protection devices should not rely on the earth point of the main supply if the generator is switched on.

An earth electrode should be installed according to SANS 10199, if there is no existing earth electrode. The earth electrode should be bonded to the consumer’s earth terminal, as well as to the earthing point of the alternate supply by a conductor of at least half the cross-section of that phase conductor, but not less than 6mm2. It should also be noted that an earth electrode is normally not required for an electrical installation in a TN system, and that protection of photovoltaics can be done by means of surge protective devices.

A system that consists of supplies from a combination of transformers and alternative supplies that are located near each other must have the neutral points of the items connected to a single earthed neutral bar. This earthed neutral bar must be the only point in the installation where the neutral is earthed. Earth leakage devices that are part of the installation should be positioned in such a way so that incorrect operation is avoided due to the existence of any parallel neutral/earth path.

Additional requirements

The following are additional requirements for installations that incorporate electrical supply derived from static inverters used with uninterruptible power supply (UPS) equipment, and both off-grid and on-grid photovoltaic installations:

  1. The output of the unit should have an overcurrent protection device installed which is designed to disconnect the output of the unit in the case of overcurrent or earth faults that may occur. The impedance of the earth loop as well as the internal impedance of the unit must be in accordance with section 8.6.5 of SANS 10142.
     
  2. An earth leakage protection device for the alternative supply is needed for that part of the installation if a common neutral and bypass switch is used.

In Part 2 of the series, we continue to unpack the requirements as laid out in SANS10142.

Stay tuned to learn more about overcurrent protection, identification of DC conductors and the additional requirements PV installations.

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