Replacing CU: 16mm or 25mm SWA?

[Ragnar_AT]

I seem to remember that the limit is 3 m.

 

[sparkwright]

How long would the cable run be?

 

[EFLImpudence]

I seem to remember that the limit is 3 m.

No, any such cable is supposed to be fused if longer than 3m.

This is said to be stipulated by the DNO.

 

[Adam_151]

I assume there is clear guidance in the reg's about how long tails can be?

There is no limit per see as how far you can run tails. What there is, is a requirement that for any part of your installation that relies on the supplier's equipemnt to provide protection. i.e. teh tails up to whatever your first piece of switchgear is. They must grant you permission to do so, generally the accepted thing is that the DNOs automatically say you have that permission for upto 3m of tails, installed surface. and while in theory you could try and negociate more, in practice trying to find someone who has the Understanding, Authority and inclination to allow you cany different is likely to be an unhill struggle. Once you get to your first piece of switchgear and that is providing protection for anything after it, you can do anything you want as long as you design it to be compliant with the requirements, hence after a switchfuse, you can use SWA and run that for whatever distance your design allows. There is nothing to say you couldn't run whatever distance of tails you wanted after your switchfuse either, and if you have tails in, and out, you can get away with a KMF style switchfuse >CLICKY<

 

[wizbongre]

I suspect the differing opinions is driven by the fact I’m close to this perceived threshold of 3m.
There’s already about 3 different flavours of switch and switch fuse between the service head and existing CU! It’s a right bugger’s muddle!

If I’m understanding all this so far: we don’t need SWA but do need protection post tails. A switch fuse as per Ragnar’s link could be one option, and indeed it may be easier using long tails from a switch fuse rather than SWA due to terminating SWA, especially large diameter SWA.

So it would end up as:

Service head -> DNO isolator -> meter -> short tails -> switch fuse -> long tails -> CU.

The long tails bit could be tails or SWA.

 

[EFLImpudence]

I suspect the differing opinions is driven by the fact I’m close to this perceived threshold of 3m.

Not really.

There’s already about 3 different flavours of switch and switch fuse between the service head and existing CU! It’s a right bugger’s muddle!

Ok - tidy it.

If I’m understanding all this so far: we don’t need SWA but do need protection post tails.

You don't need SWA.
You don't need protection by a fuse either; it is just stipulated (for no valid reason) that you must have one.

A switch fuse as per Ragnar’s link could be one option, and indeed it may be easier using long tails from a switch fuse rather than SWA due to terminating SWA, especially large diameter SWA.

Yes.

So it would end up as:

Service head -> DNO isolator -> meter -> short tails -> switch fuse -> long tails -> CU.

The long tails bit could be tails or SWA.

Yes - except -

you have an isolator before the meter???

 

[wizbongre]

"Tidy it"

Yep, that's the plan. Step one is a new CU and first lighting circuit. Then the rest can be transferred over/extended as we work through the house. End game is nothing left of the old mess.

"You don't need..."

Surely if the reg's stipulate then we need it? Being pedantic about it obviously but my logic is if something is stipulated/regulated, then we need it (no matter how true that may be in practice.)

"you have an isolator before the meter???"

Good spot! No, we don't. Memory was playing tricks on me. It should be:
Service head -> meter -> Isolator -> etc. etc.