3mtr Rules

[Paul505]

If your CU is 6 mtrs away from the main incomer and all the cabling is 25mm, can you get away with just having an isolator installed within the 3mtrs from the meter/cutout or is that frowned upon by the DNO. What i mean is do they expect you to have switched fused protection on your side because your relying on their main cutout fuse over that length of cable.

 

[MarkieSparkie]

If your CU is 6 mtrs away from the main incomer and all the cabling is 25mm, can you get away with just having an isolator installed within the 3mtrs from the meter/cutout or is that frowned upon by the DNO.
No (DNO will not be amused)

What i mean is do they expect you to have switched fused protection on your side because your relying on their main cutout fuse over that length of cable.
Yes, Switched Fused Isolator installed within 3m of the Cutout on the consumer side of their meter.

See comments within the Quote.

 

[Rockingit]

You need a fused isolator within your 3m, yes. Though of course it depends on the installation loading if you feel the need to carry it on in 25mm or not. For example, if it was a one bed bungalow then you could probably take your 25mm run to wherever the isolator needs to go, then fuse down to 60A and use 16mm from that point.

 

[Paul505]

Okay this is what i already have... Meter 100 amp cutout> 1mtr of 16.0mm tails > old 70 amp D/pole mcb Dorman Smith Loadmaster BS 3871> 5-6mtrs of 16.0mm twin/earth cable> then CU. (3 bed house)
It was highlighted to me from another electrician to me, who carried out a periodic that the cable needs to be upgraded to 25.00mm swa because its undersized and the portion of tw/e cable that runs down 1mtr to the CU in the stud wall is un-protected (50mm rule)
I understood the bit about the protection (50mm rule) but not the reason about upgrading the size of the cable, which i thought was only recommended for new builds or old installations where the distribution cable is relying soley on the 100 amp fuse.

 

[Rockingit]

Okay this is what i already have... Meter 100 amp cutout> 1mtr of 16.0mm tails > old 70 amp D/pole mcb Dorman Smith Loadmaster BS 3871> 5-6mtrs of 16.0mm twin/earth cable> then CU. (3 bed house)
It was highlighted to me from another electrician to me, who carried out a periodic that the cable needs to be upgraded to 25.00mm swa because its undersized and the portion of tw/e cable that runs down 1mtr to the CU in the stud wall is un-protected (50mm rule) are they buried or surface? Either way, if they were there before then they would have complied, so assuming that they are still 'safe' then no need to worry.

I understood the bit about the protection (50mm rule) but not the reason about upgrading the size of the cable, which i thought was only recommended for new builds or old installations where the distribution cable is relying soley on the 100 amp fuse. 16mm on a 70A MCB is fine (based on what you describe). If all you are doing is a CU upgrade (presumeably?) then the loading characteristics aren't qoing to change.

See comments

 

[Paul505]

Thanks MarkieSparkie... exactly what i thought, just wanted to confirm.
Little bit out of date with certain things, just wanted to refresh my mind...

 

[Paul505]

Rockingit...
The 16.0mm Tw/E cable runs from the meter cupboard through the wall then under the floor upstairs, then down 1mtr inside the stud wall to the Cu. The stud wall bit is the portion of cable which is less than 50mm both sides of the wall which is unprotected. Or shouldnt i worry as you have said above....
I will be having a CU upgrade but i wont be doing it as i am not Part P registered, even though i am fully qualified and i am not sure how much it will cost to go down the other route, notifying LABC then doing it myself. The sooner they erase Part P the better...IMO ( Its not very well policed plus normal folk dont understand it aswell) Sorry....going on a bit, that should be for another thread....lol

Thanks for your reply by the way...