Required tails 4 meters long question

[Marvin]

Does the electrician need to put a breaker in the tails as they are 4 meters long? Different DNO's seem to say different things.

 

Also told that Tails must be surface mounted in trunking. Client doesn't want this!! 

 

Oh happy days.

 

 

[TonyT]

Not a breaker a fuse

Dno fuse protects tails for the first 3 m anything else your own fuse is required.

 

 

[Temp]

1 hour ago, Marvin said:

Also told that Tails must be surface mounted in trunking. Client doesn't want this!! 

 

I believe tails buried less than 50mm would need to be RCD protected in the meter cabinet.

 

Many houses (mine included) have them run in the cavity but I don't think that's really allowed if you go by the book.

 

Might be possible to use SWA tails not buried over 50mm but I'm not an electrician.

 

 

[TonyT]

Yes would need 30mA RCD protection if under 50mm.

so make the wall thicker at this point 😁or as Temp says run Swa surface to forgo the RCD protection.

 

 

[Marvin]

1 hour ago, TonyT said:

Not a breaker a fuse

DNO fuse protects tails for the first 3 m anything else your own fuse is required.

 

 

Hi @TonyT

 

Thanks for this. Does this mean a 30ma RCD can be in the meter box at the start of the 4 meter tails? 

[dpmiller]

depends, might need to be 100mA time delay to give sufficient discrimination

[Marvin]

18 minutes ago, dpmiller said:

depends, might need to be 100mA time delay to give sufficient discrimination

Between the inline and the consumer box one??

[Nickfromwales]

49 minutes ago, dpmiller said:

depends, might need to be 100mA time delay to give sufficient discrimination

Only required if 2 differing RCD's are employed pre-CU?

I've only ever installed an 80a switch-fuse at the meter when conveying tails of 3+m and above, and this is never a problem (no RCD required for the last few) but I'm not over the 18th edition like a rash tbh.

If run in SWA there should be no requirement for RCD, but it may be requisite where the tails are sub 50mm from surface. You can screw into a live tail and make the fixing live, but with a SWA you'd have to short live to steel armour, so the tails need to be further away from 'attack' and the SWA less so.

[Mattg4321]

10 hours ago, dpmiller said:

depends, might need to be 100mA time delay to give sufficient discrimination

This won’t comply. If cables are run less than 50mm within the wall they need 30mA RCD protection. 
 

Either run swa, bury the tails deeper, or cover them with something impenetrable by sds drill - 3mm steel plate etc. 

[Nickfromwales]

3 hours ago, Mattg4321 said:

3mm steel plate etc. 

That's what I did on a build in Gravenhill. MBC TF so only a 35mm service cavity to lose the tails within, and SWA just would have been impossible to get where I needed it to go. Flat bar from B&Q iirc, and shows up well with a stud / metal finder.

[dnb]

It depends on the earthing scheme to a point as well. I'm on a TT earth so ended up with SWA and a 100mA RCD + 80A switch fuse box. (But my tails were a slightly silly 20 metres...) Suspect you are on TNCS earth so you'll only need SWA or RCD. I do have a blue book, but I left it on site - @Marvin happy to let you have a read of it and the on-site guide if you want since you're local to me.

 

I might even have a spare length of 25mm2 SWA getting in the way, although it might be a fraction too short.