7.12 Alternative supplies

[ians]

Time to sit down put plug in the airpods with background sounds and review section 7.12

What are the requirements .. .the way I read it.

Labels labels labels and as many more labels and notices on each DB.

Indicator - A din mount light next to the main switch is my preference.

Change over switch as per requirements.

As per requirements - earth leakage protection for plugs ... I am still trying to understand why people insist on installing earth leakage on the supply to the inverter ... I can understand samll plug in UPS ... but not a 5 kva inverter connected directly to a DB.

V-O-V type generators not to be connected to the "fixed" electrical installation.

[ians]

Earthing requirements...

Where there is no earth spike already installed ... a suitable one must be installed and bonded to the consumer earth terminal with a wire at least half the thickness of the phase conductor ... but not less than 6 mm.

But this note is rather interesting ... deosnt his mean that if you install a spike you dont need an SPD ... or if you install an SPD you dont need the spike.

NOTE 2 Protection of photovoltaics can be by means of or surge protective device
(SPD).

This section is one that seems to be a little confusing for many.

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).

[ians]

AC and DC must be mechanically separated and labeled.

The single line diagram must be displayed at the DB.

[Derlyn]

Time to sit down put plug in the airpods with background sounds and review section 7.12

What are the requirements .. .the way I read it.

Labels labels labels and as many more labels and notices on each DB.

Indicator - A din mount light next to the main switch is my preference.

Change over switch as per requirements.

As per requirements - earth leakage protection for plugs ... I am still trying to understand why people insist on installing earth leakage on the supply to the inverter ... I can understand samll plug in UPS ... but not a 5 kva inverter connected directly to a DB.

V-O-V type generators not to be connected to the "fixed" electrical installation.

Another question.

Why is it not a requirement that a generator have a built in earth leakage ?
I mean, after all there are socket outlets on a genny where all sorts of appliances are plugged in.

Derek

[ians]

The use of screw type and not compression type metal conduit ... so no bosal conduit on the roof top ?

the job I am watching being installed on the roof of a garage ... I wonder if PVC piping and trunking is allowed ... let see as we dig deeper.

[Dylboy]

That an interesting one 5.4.4.6

The use of screw type and not compression type metal conduit ... so no bosal conduit on the roof top ?

the job I am watching being installed on the roof of a garage ... I wonder if PVC piping and trunking is allowed ... let see as we dig deeper.

Is that in Ed 3?

And then the AC DC mechanically separated is an intresting one as well!

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[Dylboy]

The last bit is where I get muddled up. It may be a case of someone sitting me down and explaining and then answering all my questions I have to then understand.

The whole neutral earth bar bit is tricky. I have seen inverters that output need an "earthing box" so as when it kicks in the alt supply the N and E are bonded but when grid is back then it dissconects and the N is now floating... why can it all not be joined to incoming E and then joined to the N to all be the same.??

I may be missing something very simple but it seems very complex for no reason..

They say the N and E shall (i think its a shall)be joined on the supplier side only so if that's the case for not perm joining the inveter output N to E I think they must rethink or at least I must be taught why it must be so.



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[ians]

functional earthing requirements ... this is gonna required more attention ... need to wrap my head around this.

[GCE]

They say the N and E shall (i think its a shall)be joined on the supplier side only so if that's the case for not perm joining the inveter output N to E I think they must rethink or at least I must be taught why it must be so.



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Basically ,only the supplier may earth the neutral - You can become the supplier on the load side of a generator or inverter .

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.

You will see that this is also stipulated in municipal bylaws and Eskom bylaws since the day dot.

The reason behind the reg is to prevent fires and I will take an extreme case as an example.

My house is fed from the municipal cable network and I take 80 Amp single phase supply.The neutral is earthed at the substation transformer, 800KVA
If I then install an inverter and bridge my inverter neutral to earth with a 6sqmm or 4sqmm wire as the inverter is only 1KVA, and that inverter neutral is direct connection to municipal neutral.

If for some reason the municipal earthed/neutral comes loose or is stolen my house neutral/earth now becomes the earth/neutral for the 800KVA transformer and all imbalanced load will flow through my 16sqmm mains cable and then through my 4sqmm neutral to my inverter which is earthed
That 4sqmm wire could be in my roof space , overheat due to the current flow and cause a fire .
That earth neutral current flow could be as high as 200Amp on an imbalanced load.

That is the though process for that particular regulation

[Dylboy]

Basically ,only the supplier may earth the neutral - You can become the supplier on the load side of a generator or inverter .

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.

You will see that this is also stipulated in municipal bylaws and Eskom bylaws since the day dot.

The reason behind the reg is to prevent fires and I will take an extreme case as an example.

My house is fed from the municipal cable network and I take 80 Amp single phase supply.The neutral is earthed at the substation transformer, 800KVA
If I then install an inverter and bridge my inverter neutral to earth with a 6sqmm or 4sqmm wire as the inverter is only 1KVA, and that inverter neutral is direct connection to municipal neutral.

If for some reason the municipal earthed/neutral comes loose or is stolen my house neutral/earth now becomes the earth/neutral for the 800KVA transformer and all imbalanced load will flow through my 16sqmm mains cable and then through my 4sqmm neutral to my inverter which is earthed
That 4sqmm wire could be in my roof space , overheat due to the current flow and cause a fire .
That earth neutral current flow could be as high as 200Amp on an imbalanced load.

That is the though process for that particular regulation

That makes all the sense! Thank you for taking the time to explain! I should have thought of the PEN fault. I really appreciate it !

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