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Thread: Neutral earth bonding on backup systems.

  1. #1
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    Neutral earth bonding on backup systems.

    It seems there little confusion amongst electricians with regards to when you should do neutral earth bonding and when you shouldn't, types of earthing systems and which are used and when.

    Some say you have to permanently bond an inverter and others believe a relay must be used to prevent circulating currents and other.

    Some cant tell the difference between a generator and a UPS and wiring configuration required for each.

    A generator doesn't have an internal changeover switch so an external changeover over switch is required. It all by law doesn't require islanding mode, but does require mechanical isolation to prevent both supplies running together.

    An inverter/UPS on the other hand is different beast, with all sorts of complex electronics, bi-directional flow on the input, a built in changeover switch and required by law to go into islanding mode when the grid power switches off.

    What are your thought on earth neutral bonding for a generator and a UPS, is it the same thing?

    Do you feel a relay should be used to bond the neutral/earth or permanently bonded on the output of the inverter.

    Do you feel the SANS regs adequately cover this topic.

    But most important do you understand the different earthing systems feeding the property and why you actually require a neutral/earth.

    When a neutral/earth bond is dangerous.

    What are the implications of neutral earth bonding on the property if the earthing system a TN-S

    Can you go from a TN-C to a TN-C-S to a TN-S all in one elctrical installation.

    Who thought this could become so complicated, add a bidirectional hybrid inverter with a generator and a few solar panels and boy do we have a mix.

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    100% this is not covered enough and also not at all.

    There are a lot of things I agree. TN-C-S can be dangerous, so knowing if yo use a relay or permanent bond is important, also will it ever change.

    With inverters is it an appliance so bonding the output permanent will it matter ?

    There is so so much to learn and to try and learn is very difficult.

    Not enough training of what matters as most who install don't even know what the Earth is for other than a draw wire...

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    Quote Originally Posted by Dylboy View Post

    With inverters is it an appliance so bonding the output permanent will it matter ?

    There is so so much to learn and to try and learn is very difficult.

    Not enough training of what matters as most who install don't even know what the Earth is for other than a draw wire...

    Sent from my CPH2197 using Tapatalk
    We are listening to too much noise being create by so called Solar experts that have never studied or worked in the electrical industry , picked up scraps and trying to make it sound like there are no regulations so they can continue without abiding by any rules .

    An inverter is not an appliance . ( That is solar talk for I don't have to be an electrical contractor or issue a COC to install an inverter.)

    An inverter is " electrical equipment " as per definition in SANS 10142-1

    3.32
    electrical equipment

    item or any combination of items, including wireways, which is used for the
    generation
    , conversion (such as of voltage or frequency), transmission or
    distribution of electrical energy


    and is part of the electrical installation as per definition 3.33 and definition 3.16

    3.33
    electrical installation

    machinery, in or on any premises, that is used for the transmission of electrical
    energy from a point of control (see 3.56) to a point of consumption
    (see 3.55) anywhere on the premises, including any article that forms part of
    such an installation
    , irrespective of whether or not it is part of the electrical
    circuit, but excluding


    3.16
    consumer

    person who is supplied (or who is to be supplied) with electricity by a supplier
    (see 3.77); or a person who supplies his own electricity



    Now if you now start thinking electrical and check regulations for Electrical the rest becomes str forward .

    An inverter is treated the same way as a generator - 7.12

    7.12 Alternative supplies
    NOTE Alternative supplies include but are not limited to low-voltage generating sets,
    photovoltaic (PV) installations, gas generators, diesel generators, wind turbines and
    hydropower plant.


    Reset the mind- forget all the Solar talk noise from people who are trying to convince themselves and clients , that it is not electrical.

  4. Thank given for this post:

    Andrew_van_Zyl (23-Nov-22), Dylboy (03-Nov-22), Isetech (03-Nov-22)

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    The earthing

    When a generator is connected to an installation and you running off mains you may not earth the neutral ( 6.1.6 ) - when mains fails and the generator supplies power you must earth the neutral - This is why you use a D/pole change over or 4 Pole change over

    Same story with an inverter - The mains is fed directly to the output during mains on - When mains fails then the relay switches and you feed power from the Inverter/Battery side of the relay .
    Some units automatically bridge neutral earth others you need to do the bridge .
    To find out if it has an automatic bridge , carry out loop test , if the readings are crappy then it does not have and you need to make a plan .
    On a generator you would open the terminal box on the genset and install a bridge wire . On an inverter you would need to open the unit trace the circuits , find the relay and install a bridge on the correct side of the relay. Electricians fingers are to big to work inside those little boxes and warranties could become a problem along with grid tie circuits so it is easier to just install a relay/contactor on the output of the inverter that will do the bridging where our big fingers can work in peace.
    If the inverter has an output to operate that relay , easy , if not then use the mains to power the relay and when mains falls away the bridge between earth and neutral happens through the relay/contactor.

    I have had one of my guys get that confused look with a relay until you explain it is a light switch , just has burst of power to change the state of it , not a finger.

    If you think it is not covered in the regulations then look at 7.16.4
    When Mains fails then the inverter becomes the supply and you need to ensure that it passes the tests

    Remember that a test report needs to be done for mains supply and for alternative supply when it is on .

    If you listen to solar talk - They say tick alternate supply , job finished - A BIG NO - Tick alternative supply then another test report needs to be attached to the COC ( 8.6.1)

    The regulations are there , they explain most of what needs to be explained just don't get confused with Solar talk


    8.6.1 General
    NOTE Conduct all tests and complete a copy of the test report for each distribution
    board and supply (normal and alternative supplies). Amdt 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


    7.16.4 Neutral earthing
    7.16.4.1 Whereas TN-C systems may be implemented along the distribution
    system backbone, the individual service connections at every distribution
    kiosk shall be TN-S.
    7.16.4.2 From the point of supply to each user or part of a communal
    installation, the neutral and earth conductors shall be separate conductors.
    7.16.4.3 Wherever the neutral is connected to the earth, a warning notice
    shall be fitted to the outside of each distribution kiosk in the distribution
    system, indicating "Neutral earthed inside".
    7.16.4.4 A clear notice shall be fitted at the combined neutral-earth
    connection inside each distribution kiosk in the distribution system, that
    prohibits the removal of this connection while the supply is alive, or might
    become alive.
    7.16.4.5 The neutral shall not be earthed beyond any earth leakage unit.
    7.16.4.6 A TN-S system shall not be converted to a TN-C system.

  6. Thank given for this post:

    Dave A (04-Nov-22), Isetech (03-Nov-22)

  7. #5
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    Didn't you do PV training?

    Quote Originally Posted by Dylboy View Post
    100% this is not covered enough and also not at all.

    There are a lot of things I agree. TN-C-S can be dangerous, so knowing if yo use a relay or permanent bond is important, also will it ever change.

    With inverters is it an appliance so bonding the output permanent will it matter ?

    There is so so much to learn and to try and learn is very difficult.

    Not enough training of what matters as most who install don't even know what the Earth is for other than a draw wire...

    Sent from my CPH2197 using Tapatalk

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    The biggest concern is safety.

    If you bond the neutral earth, while in grid mode, would circulating current become a danger?

    IF you fit a relay and it fails, what are the dangers, the system voltage becomes unstable the N-E voltage increases to dangerous levels?

    Do you think that P1 or P3 is applicable for Annex P. P3 seems more suitable for inverters. Considering P1 indicates an external changeover, however an inverter is more like a UPS?

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    Quote Originally Posted by Isetech View Post
    Didn't you do PV training?
    No not yet, still want to but not yet, mostly I want to sit with the tech people at the big inverter companies and really learn the inner workings of each one. Each inverter has its proprietary things and knowing that will help a lot.

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    GCE you right, lots of noise and talk...

    It is a generator.

    It takes me a full week plus some to do an inverter, I know guys doing them in 2 days... The amount wrong in them all is plenty. They get in a spark to do the DB and they mount pretty looking invertes on a wall that fail a lot of things

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    Why is everyone referring to an inverter as a generator and not a UPS? It looks like a UPS, it has batteries like a UPS, it converts DC to AC like a UPS, It even has the same output voltage reading as a UPS, it has a display like a UPS, it must be a UPS.

    If it looks like .... , it smells like .... it must be ....

    Quote Originally Posted by Dylboy View Post
    GCE you right, lots of noise and talk...

    It is a generator.

    It takes me a full week plus some to do an inverter, I know guys doing them in 2 days... The amount wrong in them all is plenty. They get in a spark to do the DB and they mount pretty looking invertes on a wall that fail a lot of things

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    Quote Originally Posted by Isetech View Post
    The biggest concern is safety.

    If you bond the neutral earth, while in grid mode, would circulating current become a danger?

    IF you fit a relay and it fails, what are the dangers, the system voltage becomes unstable the N-E voltage increases to dangerous levels?

    Do you think that P1 or P3 is applicable for Annex P. P3 seems more suitable for inverters. Considering P1 indicates an external changeover, however an inverter is more like a UPS?
    The biggest problem with bonding earth and neutral while on mains is that if the star point at the minisub comes loose your star point could be the point for the complete minisub .
    That 6sqmm or 4sqmm wire could look like a glow plug if you become the star point on an 800KVA minisub

    A double pole CB feeding the inverter should then trip with the neutral currents

    It is why 6.1.6 was written and why the municipalities all have it written into the bylaws

    If you don't earth neutral when running without mains then no protection will work in the event of an earth fault .
    Last edited by GCE; 04-Nov-22 at 07:31 AM.

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