Burying BT dropwire or CW1128 cable

[ARW]

100m of

I suppose it depends on where you buy it from:-)

[ARW]

That's still not a bad price. I paid £14.40 + VAT for 10m of 2.5mm 3 core last week.

[ARW]

What size MCB are you going to use and what earthing type do you have at the house?

You could be getting close to limits if it's a 20A MCB and a 62m run.

[nothanks]

I agree. In the past I've bought from Quickbit but this time Superlec Direct were cheapest

[nothanks]

Perhaps it's made from oxygen-free copper ;-)

[nothanks]

Ahem, it's a little more complicated.

The house has an overhead 2-wire feed, earthed at the last pole to give TN-C-S. I've added an additional earth rod at the main CU.

The main CU feeds a number of things: - electric shower, cooker, EV charger, some lights and a ring - two underground SWA sub-mains (one 2.5mm and one 4mm) to sheds with their own CUs (which have TT earthing) - a 16mm2 T&E (with additional parallel 16mm2 CPC) sub-main to a second CU elsewhere in the house - about 20m

The second CU feeds the majority of lights and rings BUT also has a B20 MCB feeding a 2.5mm T&E cable that becomes SWA when it goes underground (50m, perhaps) to an external CU (with TT earthing) which feeds the Well pump and provides a 13A outside socket via RCBOs. The 62m sub-sub main to the gate will come from this external CU and will be TT-earthed. The MCB protecting this last cable will be B6 or B10.

All comments gratefully received.

Phew, I really must draw a diagram so someone else will be able to make sense of everything when I have popped my clogs or lost my marbles.

[ARW]

I was going to say "you really make things hard" and then upon editing decided not to for obvious double entendres.

[nothanks]

I don't usually have that effect on people on newsgroups ... AFAIK ;-)

More seriously - I don't know how else it could have been done. The supply comes-in to an attached garage at one end of the house, which is quite long and L-shaped. It already had a (under-sized) sub-main to a couple of Wylex fuse boards (one for lights and one for sockets) in the centre of the house. If I'd taken all the internal circuits back to the main CU I'd have needed to extend lots of cables, and used 4mm2 in places because of the distances. The supplies to the sheds were, initially, overhead and the Well hadn't been used since the 60s so these sub-mains were all new ... lots of digging!

[John J]

I'd opt for a duct of some description. It's always an advantage if you want to replace the cable or add another one (or more) in the future.

[ARW]

Depending on what fault conditions occur and depending how you have separated the earth on the SWA from the second consumer unit to the external CU then the metal case could become live without removing a screw.

And a chopped down CU? That is brilliant. Not sure it meets or fails the regs but I love it.

[nothanks]

T&E from the second CU (with a parallel CPC, 2.5mm2 I think), connected to the SWA in an adaptable box with shield connected to CPC. SWA shield insulated at external CU. Earth bar in external CU connected to earth rod, case and door of external CU connected to earth bar, shield of SWA to the gate controller connected to earth bar. Gate controller connected to its own earth rod.

The only way the case could become live would be if the cable to the earth rod was damaged. What's the best way to protect the cable from the earth bar to the earth rod?

It was one of those temporary things that has stayed. I'd just replaced the plastic CU so I thought "chop-out the central 9 ways and glue the ends back together (lid, case and cover) to produce a 5 way and put it in a lockable IP65 enclosure, mounted to a post".

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