Cable run to feed a sub DB

Electrical Fundamentals. AC power.
1

Hi all

I want to install a new cable from the main 3-phase DB to feed a single phase sub DB on my property.

According to code, can / may this 16mm AC cable run against a outside wall of the house in conduit of course, then go down to the ground and continue the run under ground?

The run against the outside wall will be around 10m and then a further 10m or so under ground if that makes any difference.
It will be high up against the outside wall because it will have to pass above 2 doors.
Come to think of it, I recon the cladding on that wall is pretty thick, so I might be able to cut a channel for the conduit and then plaster over it again.

I intend doing the hard work and then getting my sparkie to come wire it all up and issue a CoC.

2

I’m not sure what the current sparky’s are using for underground (twin & earth?) but I would install a SWA cable…

3

Why, if the entire cable run will be in conduit?

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4

Fair enough but what type of conduit are you going to use?

5

The way I roll on the farm is to usually run cables underground in old black water pipe, but for this I can use real conduit as well if I have to.

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6

The big problem I’ve found with conduit underground is water collecting in it.
So your PVC pipe is a good idea since there are no joins.
Also consider polycop pipe. This is really robust stuff and way better than Pex for this kind of application IMHO.

7

Ultimately people do the cheapest thing that complies with regulations.

The wire must run in some sort of protected raceway. So either armoured cable, or some kind of piping.

SANS-10142 only says it must be buried at least 0.5 meters deep.

Typically the material must be rated for the task, which is why normally water pipe is not allowed (might not have the right fire rating).

And conduit with some twin and earth is obviously a LOT cheaper than armoured cable.

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8

When I bought the place, the sparkie who fixed a couple of things before I moved in actually used old water pipe for some cable runs, plus it wasn’t even 50cm deep.
Plus he gave me a CoC, so it seams some guys work according to their own standards.
I didn’t find the depth of the cable runs acceptible at the time so fixed it myself afterwards, but I left it in the pipes.

I actually found other dodgy things in the electrical installation much later, which made me doubt his CoC even more. One of those not worth the paper it is written on, but if I look for the guy today, I probably won’t even find him.

9

The pipe is buried in the ground, so as far as fire goes, it’s probably fine. It protects the cable. And from my experience with the black PVC piping we use on farms, they don’t really participate in a fire anyway, although it is unclear what would happen if they got hot enough.

In short, I probably wouldn’t dig it up just to change it over. But for a new run, I might use something else. Conduit is cheap enough. I also don’t like the water ingress issue though, to be honest, but that also happens with other piping. Hot moist air enters from outside during the day, and cools down and condenses in the pipe. It always happens.

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10

I saw pipe melt in a veld fire at a neighbour last year, but it was where it ran above ground for10m or so, he just cut out the melted pipe and put in a new piece, it was still fine where it gone under ground.

My intention is exactly that, to do everything as per code going forward.

I never actually considered fire with the ethernet and coax cables I buried in pipe, the main reason why I did it was to avoid future accidents with garden forks.

11

Veld fires can travel through holes made by animals, so I imagine it could under the right conditions also travel through any PVC pipes including conduit. But I think the main point for electrical installations is that an electrical fault that causes an arc should not be able to start a fire. Say for example the arc lasts some seconds before a breaker kills the current, if the plastic self-extinguishes you are fine, and if not, you have a problem.

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