There have been many questions about whether one permanently bonds the output of an inverter and there are numerous opinions around the matter.
The ECA(SA) has referred the matter to the Department of Employment and Labour and South African National Standards for deliberation and clarification from official sources and await feedback.
In the interim, the National Technical Committee has deliberated the matter and clarified the requirements/interpretation in SANS 10142-1 which the committee feels is relatively clear.
Pointers from ECA’s National Technical Committee
- There shall not be a permanently connected bond between the earth and the neutral downstream of the main switch (point of control). a, b, c
- There shall be an arrangement (device/ switch/ contact/ relay/ changeover switch etc.) to bond Neutral to Earth while fed from an alternate supply. c, d
- The earth neutral bond must be removed when the mains supply is connected. c, d
- Specific to the installation of inverters when the grid is connected you rely on the supply authority neutral- earth bond during this parallel operation and your bond on your device must not be present, during islanding condition the bond on your device must be present.
- Manufacturer’s instructions on how this arrangement is maintained and installed must always be consulted. e
- The onus to confirm compliance remains with the installer to verify.
CITATIONS
a SANS 10142-1 6.1.6 The neutral conductor shall not be connected direct to earth or to the earth continuity conductor on the load side of the point of control except as allowed in 7.16.4.
b SANS 10142-1 6.12.4 Earthing of the neutral of combined sources
When an installation that has a common neutral is supplied from a combination of transformers and generators located near one another, the neutral terminal of each of these items shall be connected to a single neutral bar. This neutral bar shall be the only point at which the neutral of the installation is connected to the consumer’s earth terminal except as in the case in 7.12.3.1.3 or 7.16.4.
C SANS 10142-1 7.12.3 Earthing requirements and earth leakage protection:
7.12.3.1 Neutral bar earthing
7.12.3.1.1 Protection in accordance with the requirements of 6.7 shall be provided for the electrical installation in such a manner as to ensure correct operation of the protection devices, irrespective of the source of supply or combination of sources of supply. Operation of the protection devices shall not rely upon the connection to the earthed point of the main supply when the generator is operated as a switched alternative to the main supply.
Where there is no existing earth electrode installed in the electrical installation, a suitable earth electrode may be installed in accordance with SANS 10199. When installed, the electrode shall be bonded to the consumer’s earth terminal and to the earthing point on the alternate supply by a conductor of at least half the cross-section of that of the phase conductor, but not less than 6 mm2 copper, or equivalent. This also applies to a single-phase supply (see also 5.2.3.1).
NOTE 1 In a TN system earthing of electricity supply, an earth electrode is normally not required in an electrical installation.
NOTE 2 Protection of photovoltaics can be by means of or surge protective device (SPD).
7.12.3.1.2 In an installation that is supplied from a combination of transformers and alternative supplies located near to each other, the neutral points of each of these items shall be connected to a single earthed neutral bar (see P.1). This earthed neutral bar shall be the only point at which the neutral of the installation is earthed. Any earth leakage device shall be positioned in such a way as to avoid incorrect operation due to the existence of any parallel neutral/earth path.
7.12.3.1.3 Where alternative supplies are installed remotely from the installation, or from one another, and where it is not possible to make use of a single neutral bar or neutral conductor which is earthed, the neutral of each unit shall be earthed at the unit and these points shall be bonded to the consumer’s earth terminal (see 6.12.4). The supply from each unit which supplies the installation or part of the installation, shall be switched by means of a switch that breaks all live conductors operating substantially together (see figures P.2 and P.4), to disconnect the earthed neutral point from the installation neutral when the alternative supply is not connected (see also 6.1.6).
NOTE Where four pole switching is implemented, consideration should be given to use overlapping neutral switching devices.
7.12.3.1.4 Where only part of an installation is switched to the alternative supply in the same distribution board, the neutral bar shall be split (see figures P.2 and P.3).
d SANS 10142-1 7.12.6 Additional requirements for installations where the alternate supply system provides a supply as a switched alternative to the main supply (standby systems and UPS systems that incorporate bypass switching)
7.12.6.1 Precautions that comply with the requirements of 6.9 and 6.16 for disconnection shall be taken, so that the alternate supply system cannot unintentionally operate in parallel with the main supply where the supply to the electrical installation is supplied by a supplier.
NOTE 1 Suitable precautions can include
a) an electrical, mechanical or electromechanical interlock between the operating
mechanisms or control circuits of the changeover switching devices, or
b) a system of locks with a single transferable key, or
c) a three position break-before-make changeover switch (also refer to note in
7.12.3.1.3), or
d) an automatic changeover switching device with suitable interlock, or
e) other means that provide equivalent security of operation, or
f) an inverter (if it complies with IEC 62116).
NOTE 2 All the protection measures for alternate supply in accordance with this part of SANS 10142 still apply.
e SANS 10142-1 5.1 General
All commodities in an electrical installation shall be installed in accordance with the requirements in this part of SANS 10142 and with the manufacturer’s instructions, where applicable.
NOTE 1 This clause contains the general safety principles applicable to electrical installations.
NOTE 2 The manufacturer’s instructions may contain more stringent requirements.
