7.12 Alternative supplies

**Dylboy** · 04-Dec-21, 08:43 AM

That first PDF I really enjoy, even though its a draft it has decent info and good practices so I follow that in conjuction with 10142-1.

Thanks for the second PDF, will read later on. Got a stuffy nose and not feeling well so retaing info is making my head explode haha.

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**Dylboy** · 04-Dec-21, 08:45 AM

Originally Posted by ians

Trying to understand the functional earth ... does this mean that if you connect lets say the negative conductor to the supplier earth ... you dont need to run separate earth wires with the DC cables ?

Also do we have to earth the dc side of things. Bt earth i mean for example join the Neutral of the DC battery bank to an earth spike or even the consumer installation MET or the CET ? Also then PV Negative lead must that be earthed like the battery bank ?

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**GCE** · 04-Dec-21, 10:29 AM

Originally Posted by Derlyn

@ Ians

I am talking about a portable generator, not a standby one that's connected to the installation.

I'm thinking now, how many people have been shocked while using an appliance plugged into a portable genny ?

Derek.

One of the reasons for VOV gensets on site .
The voltage to earth if you pick up a shock is 110v not 220v
A genset is generally not referenced to earth , rubber vibration pads between genset and frame - If you measure from live to ground as in earth , sand , you should measure 0V , so you cannot become the earth path

**ians** · 04-Dec-21, 10:45 AM

Originally Posted by GCE

One of the reasons for VOV gensets on site .
The voltage to earth if you pick up a shock is 110v not 220v
A genset is generally not referenced to earth , rubber vibration pads between genset and frame - If you measure from live to ground as in earth , sand , you should measure 0V , so you cannot become the earth path

You must like in the Cape

... I have never in all the time of hiring purchasing or installing a 5 kva generator ever seen a generator with vibrating pads ... other than the bigger diesel floor standing units ... we install vibration pads.

**GCE** · 04-Dec-21, 10:45 AM

Originally Posted by Dylboy

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

**ians** · 04-Dec-21, 10:48 AM

I am wondering if I should even waste my time to carry on reading the SANS ed 3 version of alternate supplies ... compared to the latest draft regs ... it is pretty useless.

The new drat makes a lot more sense the label description and everything is more up to date.

**ians** · 04-Dec-21, 10:54 AM

Originally Posted by Dylboy

Also do we have to earth the dc side of things. Bt earth i mean for example join the Neutral of the DC battery bank to an earth spike or even the consumer installation MET or the CET ? Also then PV Negative lead must that be earthed like the battery bank ?

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Dont get mixed up with the AC and DC component of the installation ... refer to the AC side as the neutral and the DC is the negative.

I am still trying to understand the logic of what I am reading ... it sounds like one of the DC conductors can be bonded to earth which will mean you dont have to run an earth wire with the DC cabling ... but just beware I am trying to makes sense of it ... I am confused myself.

**Justloadit** · 04-Dec-21, 10:57 AM

Originally Posted by Dylboy

Also do we have to earth the dc side of things. Bt earth i mean for example join the Neutral of the DC battery bank to an earth spike or even the consumer installation MET or the CET ? Also then PV Negative lead must that be earthed like the battery bank ?

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I would say No! Consult the battery or inverter manufacturer.
The Neutral of the AC side of the inverter is derived from the battery from a bridge type electronics, so in effect, the negative side of the battery and PV panels are effectively connected to the Neutral of the AC out via a Diode/FET.

Joining this to earth would damage the inverter.

To add a little bit more here. Whilst the Neutral is connected to the negative of the PV panels and battery, it is not a permanent connection, but rather a high speed switching, in which the Neutral of the AC output is effectively alternated On/Off between the battery/PV positive and negative terminals.
Only in the case that the battery/PV are isolated from the AC output may the DC negative side be earthed. However I doubt that they are isolated, as this would increase the cost and physical size of the inverter by introducing an isolating transformer.

**ians** · 04-Dec-21, 11:08 AM

Ok so I phoned a friend ... now I am pissed off because a I stalled purchasing ed 3 ... edition 3.1 was launched 2 weeks ago and by the way apparently there are many changes in the new edition and it still doesnt include the other draft that is still in draft ...

I also need to get the NRS 097 code to understand solar installations.

I enquired about the functional earth and that kind of stuff and as usual ... its never just as simple as we think

**GCE** · 04-Dec-21, 11:12 AM

Originally Posted by ians

You must like in the Cape

... I have never in all the time of hiring purchasing or installing a 5 kva generator ever seen a generator with vibrating pads ... other than the bigger diesel floor standing units ... we install vibration pads.

The alternator and petrol motor are normally fastened to the frame of a portable set with a rubber vibration pad as per attached pic