Distribution Board Not compliant with 17th edition

[bugsy]

What size are the meter tails?

 

[RWJ]

What size are the meter tails?

16mm (In OP)

 

[bugsy]

There must be a MET in there somewhere
Anyway looks like 3c swa to flat cu , I suggest upgrading earthbond to MET from 6mm to 10mm / 16mm ( check calcs though)

 

[Dave1982]

Update on this problem. from the photos. the meter has economy 7 connected which i have contacted ngo to disconnect from current meter. tails then supply 20A switched fuse which is dedicated cable run in appears 2.5 to the flat CU just for the original heating. The 100A switched fuse supplies the rest of the flat. So 2 cables neither of them are SWA both grey insulation sheathed with line neutral and earth. all wires multi stranded. there is no separate earth cable running to the flat. Only the earth within the sheathed grey cables. I doubt the I would have the approval of the owners of the complex to mess with their communal cabinets or even run a new earth cale through the communal entrance hall and corridor. The other aspect is if one needs an upgrade so do the rest.....a major upheaval to the residents I guess.

 

[Dave1982]

Cable feeding flat from switched fuse 100A from photo looks like 10mm line and neutral, earth nowhere near 16mm
https://picasaweb.google.com/lh/photo/ElERcGjqrDHgsZSoqPYgwpc6fO7wa3BWfpA11pg2i5U?feat=directlink

 

[malcolmsanford]

My advise to you would be look at the over all picture, by changing that CU to RCD protection you are leaving the installation in a safer condition and so this will give you ways to perhaps look at things differenly, but it will need calculation on your part.

Read regulation 543.1.4 it tells you that if you do not wish to calculate the size of the main protective conductor as in reg 543.1.3 then you use table 54.7 this tells you that a line conductor of 16mm or less needs a 10mm CPC. That is if you don't calculate the conductor by the adiabatic equation so that is your first step, you need to confirm that the CPC in that T + E is capable enough by calculation for the sub main distribution circuit.

I think the biggest problem you will have is the actual protection device for this T + E. Depending on the rating of the fuse, that will determine how your calculation pans out. If it is a BS 1361 60amp or less then you maybe ok. If it is larger say a 80 or 100 amp then your CPC may come out as not large enough. Luckily if it is a fuse you can use the 5 sec rating for a distribution circuit. If you do need to change the fuse to a lower type, then as your changing the circuit characteristics, you will need to then see if the circuit contravenes regulation 522.6.6 and 522.6.7, if it does as soon as you start to work on it you should provide it with RCD protection and then that brings discrimination factors into play and reg 314.1.

These older houses that have had flat conversions done in the past, will always in some way fall foul of the new regulations, but as your the designer of the new work it is up to you to prove that what work you do, that may not be totally in line with the new regulations, will leave the installation in a safer condition. These are one of the few scenarios where I think the IET have given us electricians leeway, that on the EIC you have a section with departures from the regs.

This means you will have to be sure of what your doing. You need to do the correct calculations, not once but twice, and make sure they are correct. If the calculations confirm that the T+E CPC is capable then you can go ahead with the CU change, making sure you keep those calculation with the EIC for your future reference.

 

[Spudnik]

Have to say, Malc has hit it on the head.

 

[Roger]

Just out of interest what is the Zs reading in the flat in question ?

Could you get a Ze reading if you notify other residents about a temp disconnection ?

Could you find the incoming gas and water to see if they have main protective bonding conductors in place ?

I have had a similar situation in a block of flats and the management company was very approachable about the upgrade and went ahead.

 

[Dave1982]

Zs reading in flat was 0.5 off furthest socket

 

[Dave1982]

Jason will go the way malk suggested. Will check if switched fuse is 100A rated and take it from there. thanks all for the advice much appreciated

 

[Dave1982]

ZS at consumer unit read 0.2 ohm

 

[Roger]

"Cable feeding flat from switched fuse 100A from photo looks like 10mm line and neutral, earth nowhere near 16mm"

Is that right,unless i am missing something putting a 100 amp fuse on 10mm cable is a bit dangerous or have I lost something in translation.

If so shouldn't that have a 40 amp fuse to protect the cable.The flat won't use more than that,or will it ? is it large ?
Zs would be better if you were to use a lower rating of fuse.Any chance of getting a Ze ?
I upgraded all over 10 and 16mm to comply,16 meter run on 10mm and it made .01 difference on my Zs.
But it had to be done,with so little circuits I would use RCBO's throughout as the price seems to be getting better and better these days.

 

[oldtimer]

Dave first of all check the size of the fusewire back at the MEM switch fuse I assisted a guy who took it for granted that there was a bit of 60 amp fuse wire fitted until I prodded hime to take it out and found a bit of 2.5mm copper accross it. Might be an idea to change it to a cartridge fuse and carrier me thinks you can buy these or if there is an isolator secton fitted there nothing stopping you fitting a circuit breaker within the enclosure.

As for your delima well Malcolm me thinks you are spot on and depending on the age of the building you may find that it was designed originally with small power and a couple of light circuits and since then the extras have been the cooker and the shower circuits and yep I agree you are not upgrading the board to take another wing on infact you are picking up the same circuits and making it safer so my view would be the mains can look after themselves at a later date. I was called out a couple of weeks ago where the tenant thought "any fool can change a shower pull cord switch" so when it went bang he actually (I thought) tripped the main fuse so I sorted his pullswitch and he called out the DNO who found it was not the main service fuse that had blown but the one in the cupboard at the bottom of the stair.

One thing that niggles me here I remember asking about a situation years ago where the supply cable to the flat was not big enough ie 10mm istead of 16mm but I was told that due to the short cable run then 10mm was ok as it could take the load. Mind in my house I have a imperial version of 10mm micc supplying my board.