Garage cable

[Essex]

Just a quick question

Looking to put in a garage CU (2-way 16A and 6A).

The main CU is 17th edition with 100A main fuse, 25mm tails and 16mm earthing.

If I henley the tails and run a SWA to the garage, does the cable need to be 25mm or can I get away with a smaller cable?

Thanks

 

[kme]

Ah, well, see.............................

That is going to depend on a number of factors we don`t (yet?) know.....

How long is the cable?

What OCPD were you thinking of having at the front end?

What is the earthing system?

 

[NozSpark]

No..

The SWA must not rely on the DNOs fuse for protection, they only allow short lengths of tails (up to 3m IIRC)

So split the tails with a henly block into a metal clad switch fuse and then gland the SWA onto that... Pick the correct size fuse to protect your SWA,,,, although you may need to RCD protect the SWA if the installation is TT

 

[kme]

If its TT, he can`t use a metalclad either, mate.....

 

[NozSpark]

If its TT, he can`t use a metalclad either, mate.....

Unless he puts the tails through a RCD before hand

 

[kme]

Aye....the RCD that is in an insulated enclosure, so might as well use for the OCPD???????????

 

[NozSpark]

There is that,,

Of up stairs now,,,

Nos da

 

[kme]

See you "later"?

 

[Essex]

System is TNC-s and the run is about 20 metres

 

[Badger]

ohhh steps will be pleased :slap

 

[a1]

I prefer it to be a REC4 to split.

 

[Revved Up Sparky]

If there is already a 17th edition CU there and there are spare ways then I would be tempted to :-

i) Fit a 32A MCB into the exisitng CU,

ii) Install a metalclad adaptable box next to the 17th edition CU,

iii) Run a 6mm 2 core SWA to the garage from the adaptable box,

iv) Install 6mm tails from the adaptable box to the CU, using an earth ring and crimped lug to take a 6mm earth back to the main earth bar,

v) Fit a 4 way CU in the garage (allowing 2 extra ways in case of future additions) containing your 16A and 6A MCB's protected by a main 30ma double pole RCD.

vi) Exporting TNCS to outbuildings is becoming an increasingly controversial issue ! IMHO because the earth and neutral are connected together at the origin and if the neutral is lost and extraneous conductive parts are not reliably connected to the MET then metalwork could become live. I personally would be inclined to terminate the SWA into an insulated enclosure, not taking the earth into the garage CU and fitting an earth rod for the garage, running your earthing conductor from the earth rod to the earth bar of the new garage CU and ensuring the Ra is < 200 ohms. Other members of this forum may suggest exporting the TNCS, uncle Steps will not... ....

 

[steptoe]

^^^

good description rev,

and yes, I would certainly be against the idea of exporting the earth to the garage.

 

[Evans Electric]

25mm SWA !!!!! What do you need ? A 100A supply ??

Just come off a spare way in the C/U with a 2.5 X 3 core. SWA

 

[Essex]

Thanks for the response guys, and a great description Rev.

There are no spare ways on the the existing CU and it looks like the house(Porch) was built around the CU which make it difficult to carry out any work on it with limited access, the easiest solution would be to split the tails from the meter into a henley block and take a new feed to the garage, as this is a parallel path I was thinking that the tails should also be 25mm with 16mm earth.

 

[SPECIAL LOCATION]

You select the size of your cables based on the load, cable length, volt drop etc....

As Deke says why pay for 25mm...?

According to your garage CU you at absolute maximum cannot exceed 16+6 =22Amps....

How far away is the garage?

10mm would be overkill

6mm would probably eat it

4mm may be OK with a little room to spare...

but 25mm !!!!! :Oheadbang

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