How does this work?

This is at my brothers new house. We are trying to figure out what’s the purpose of this box. This box is on the outside of the house.

At the bottom of the box, there is a brown, blue and green cable that goes to a generator. The generator is no longer there. The previous owner took it away when he moved out.

There are two other cables entering the box at the bottom. We have no clue where this is from.

Can anyone cast some light on this wiring ?

Seen something similar at our house. In our case, it was the feed from the street box into the house.

Those really thick wires, one from the street, the other one into the house.

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I should add that the house has 3 phase power.

Is that a change over switch that is used to switch between eskom and generator, manually ?

How can we test this out to determine which circuits are on this phase ?

Sorry, I have no clue, just posted what I saw at our house one day, accidentally, in the same box outside the house, but single phase.

The changeover, probably maybe.

Some more knowledgable people will be along momentarily.

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Its a manual changeover between the Grid and Generator. Feed to house comes out of top of Switch and 2x Sources come in the bottom.

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It’s a three phase connection. The red (L1), yellow (L2) and blue (L3) are all live (relative to black neutral).

These are the so-called “old” colours that we still use in SA. In Europe it has been replaced by brown, black and grey (with blue being neutral).

I’m not sure if this is the supply point of the house. I think it isn’t, it’s just a point for installed for connecting the generator. I will explain why.

In this box you can see Neutral is not switched, they all just tie together. This would be normal for a TN-C-S earth setup (neutral also serves as a functional ground and therefore cannot be switched), but in such cases you usually see an earth bar too, an explicit link between the two bars (your TN bond), and then an earth wire will snake away towards an earth spike somewhere on the premises. I don’t see that.

Also, there should be overcurrent protection in the live side. In the picture above there is none, just that ACDC changeover (which only isolates).

It does look VERY much like the connection point in a TN-C-S setup… so I really hope they didn’t hack this up when installing the generator.

Edit 3 (collapsing the first two): The lives of the backup side are tied together on the changeover (yellow and blue loops under the changeover), so when the generator was running everything is collapsed into a single phase system. 3 Phase loads don’t work on the generator, but all the single phase loads work (regardless of what phase they are on).

Yeah I think I see what happened. There used to be a 3-pole breaker on that rail (marked 4). The wires have all been extended (1, 2 and 3) to reach, L2 nogal with some earth cable (you can see the green and yellow).

By replacing the breaker that was in here with a changeover, I think they dropped the overcurrent protection. This probably needs attention by a sparky (even if he just disproves what I said and I end up eating my foot).

Also… the box is painted the same colour as the house. Right? It has been there a LONG time…

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It’s a manual chop-over, as overs have said.
You have 3ph in the house, but the generator was 1ph, so all phases are bridged on the bottom of the isolator when the generator supplying.
The other two cables are

  1. From the main supply
  2. To the House

The isolator could either select the main supply (3ph) or the generator. As the generator was 1 ph it put that 1ph on each of the house supply wires.

Thank you @Phil.g00 @plonkster @TheTerribleTriplet @mmaritz for your analysis and feedback.

My brother bought this house in July22.
The previous owner had a generator outside. We have no idea what generator it was. It was removed.

This box is on the outside of the garage. It near the metered box on the roadside. So it’s possibly the main entry point to the house.Yes this box has been here for a long time. My brother has made no modifications to the house. The house hasn’t been painted since moving in.

We have been trying to figure out how this would work if a generator was connected here.

Now, I’m wondering how did this pass the electrical CoC?

Edit: I suspect that this was hacked when the generator was fitted by the previous owner


Except for the lack of overload protection, this is not too bad. To connect a generator now, simply connect the black three core cable going into the sprague to a generator. I assume that is hanging loose somewhere where the original generator used to be, possibly rolled up and taped up or something.

But have the overload issue seen to. It needs a 63A breaker between your grid connection and the house, and it needs a smaller one for that generator cable (how much is that… maybe 4mm^2?).

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It was a 1ph generator because all the phases are commoned at the bottom of the isolator/changeover.

I assume there is an MCB at the meter box, which feeds directly onto the Main income on your house DB.
So it is no more than a straight-through connection with an isolator with the same size cable in and out. It is also rated to switch on load.
As the cabling is equally rated and no loads are directly fed I see no technical requirement for overload protection.
I think it just has to comply with reticulation box regulations which are less stringent than DB board regs.
AFAIK that entails, the box is lockable. Where lockable is defined as needing a tool to open.
Inserting a bolt into the thread at the bottom of the box with the lid on will satisfy that.
Then it needs labels, naming it and where it is fed from. I am unsure if regs require it to be labelled as to where it supplies but no harm. Danger electricity yellow triangle label.
Disconnect the smaller cable. It is bad practice to have a cable connected only at one end.
Your DB inside the house must also be labelled as being fed from this box.

The cable armouring between both cables will be your incoming earth and are connected to each other, which is good. Nowadays, I think new installations require a dedicated core for the earth, but it isn’t retrospective.
All in all very little to do to be compliant, if it isn’t already.
I’d involve a competent electrician before buying a generator and recommissioning this. There is more to it than most DIYers realize.
But suffice it to say your standard suitcase generator on wheels is forbidden.

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AFAIK, you only need an isolator in this box, and it might also be optional. There should be an MCB in the meter box, and one in the DB (main switch)

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It will depend if this is accessible to the customer. In my house (before I switched to prepaid) the meter box was not accessible to me. In the meter box there will be a breaker that is slower than the one on the customer side, so that the one on the customer side trips first (and you don’t have to call someone to turn your power back on).

That is to say, the lack of (additional?) overcurrent protection probably isn’t dangerous… it may just be inconvenient.

I also expect that the next stop will be in the main distribution board, which in all likelihood also has a 63A main breaker, in other words there is already overcurrent protection downstream as well.

So I will concede that maybe I got this wrong. Will depend what the regulations say. I’m almost certain they do require overcurrent at this location, but I am not a sparky.

The neutral not being switchable suggests to me that this is TN-C-S, but the earth spike must branch off somewhere else. If it has a valid CoC, they should have at the very least done an earth continuity test, so I would not be worried about that.

Absolutely agree with you here.

Essentially, you should have what Annex S.1 in SANS 10142 shows. I see circuit breakers in addition to the changeover. Don’t know how literal this is taken in practice.

Edit: If there is a circuit breaker in the meter box, and the meter box is accessible to the customer, then the CB to the left is covered. If there is also a circuit breaker at the generator, then that side is also covered. And I would say this is compliant. Right, @Phil.g00 and @_a_a_a ?

Here is a picture of the meter box on the street side.

I need a closer view of this to tell you more:
& the amperage rating of your DB Main MCB.

Also, that has orange levers. It’s the “slow trip” kind (curve 1), used to give selectivity to the faster kind that should be on your end. At least as I understand it.