UK DNO Concentric cable current carrying capacity

[Snarfsnarf]

Had UKPN come out to a property recently to upgrade the main fuse from 60A to 100A but when they arrived they said that the supply cable which he confirmed is a 25sq.mm. CNE aluminium concentric cable (1-phase, burried) for the PME supply is only able to take a 80A fuse. They will have to dig in a new supply cable (presumeably 35sq.mm) to complete the upgrade to 100A. The supply isn't looped and the meter/consumer tails have already been upgraded to 25sq.mm. so no problems there.

It seems strange to me that they say that this cable isn't able to take 100A? Looking at datasheet from Cleveland it looks like worst case is CCC of 105A.
Was the guy correct to say that 80A fuse is the max on that cable? Obviously it's at their expense to dig in the new cable but it would be much better to avoid the hassle of it all if it's not needed. I have a link to a UKPN document EDS 02-0033 which documents the current carrying capacity of some larger waveform cables from 95-300sqmm but can't find anything for domestic supply 25sqmm cable.

 

[OnlQQker]

When I was studying 12 volt high amp cables, the rule of thumb was to leave at least 20% of the cable bigger than the ampage itself after all factors had been taken into account. I times that amount by 4 on the battery cables themselves.

Perhaps they're doing the same thing now?

 

[mattg4321]

How long is the run???????

 

[Snarfsnarf]

@mattg4321
15mtrs tops.

 

[westward10]

That CCC is not for it being buried but it doesn't actually show that method.

 

[Marvo]

If it's an aluminium concentric wavecon type cable it's quite possible it's not rated to be buried unless it's ducted...

 

[R-fur]

If it's an aluminium concentric wavecon type cable it's quite possible it's not rated to be buried unless it's ducted...

It sounds like a straight concentric cable which will have a 25mm solid aluminium core surrounded with copper wires for the CNE. Quite common in the UK.
Aluminium wavecon cable was used by some UK DNOs and was rated for direct burial.

 

[Snarfsnarf]

Not sure if it is buried direct or ducted. I guess they would ducting them as a standard practice? (At least these days. Who knows what they were doing in 1980 when these houses were built).

Again, not sure if it's staight or wavecon. The guy who came said wavecon (or waveform he call it) but they wouldn't be tapping off that section so it could easily be straight.

Any ideas what CCC UKPN or other DNO's allow, and in terms of fusing whether 100A or 80A max.? I have heard that similar houses on the same road, built at the same time, were upgraded to 100A without needing change the cable.

 

[Rockingit]

Could it be because the cs of the Neutral spiral is 50% of live conductor? If so, I believe they're trying to uprade most networks to be 1:1. Just a thought.

 

[R-fur]

A 25mm Al conductor should be able to carry about 120A so a 100A fuse should be ok.
Waveform or wavecon cables are used as distributors not service cable. I don't think I have ever soon a waveform cable smaller than 70mm.
Ducting is not standard practice for distributor cables as it derates them by 30% and makes it difficult to joint services onto them.
The service cable to your place is I believe single phase so the neutral will be fully current rated, although as it could be copper it may be physicaly smaller.