Distribution Board Not compliant with 17th edition

[Dave1982]

Hi everyone.

Can anyone advise me on what to do?

I have been asked to change a consumer unit of a flat. install a seperate ring main for a newly fitted kitchen replace like for like socket outlets and light switches
I've done an inspection a nd test on all circuits and found no problems.

My problem is I have inspected the mains distribution board located on the ground floor which feeds 3 flats. each of which have fused switches protecting the cable run from the inlet to theindividual properties.

the cable is not an SWA but an imperial equivalent of what i would say was maybe 10mm Twin and earth. the cable run is approx 12mtrs. The earthing appears to be 6mm cable.

My question is if the regs require 16mm main earth cable is it my responsibility to upgrade this or the properties management companies.

The tails from the meter are 16mm not 25mm.

 

[Dave1982]

A few photos to make things clearer.

https://picasaweb.google.com/lh/photo/g4fz9gWE0C0F74lp_sjy2pc6fO7wa3BWfpA11pg2i5U?feat=directlink

 

[telectrix]

can only see 1 pic. what is the earthing arrangement?

 

[Dave1982]

https://picasaweb.google.com/lh/photo/iLHKwDaYvo34oTX3HFL2_pc6fO7wa3BWfpA11pg2i5U?feat=directlink

 

[Dave1982]

https://picasaweb.google.com/lh/photo/OT9ZnvRaosHPcRMjmvSx3Jc6fO7wa3BWfpA11pg2i5U?feat=directlink

 

[gpz900jim]

could you not just run an additional earth to bring that up to regs? I think you would probably have trouble getting the management co to do anything. A lot of them spend a minimum amount of cash on maintenance.

 

[bugsy]

Depends whi is resposible for what? is the flat meter in that riser if so whats the size of the MET from SWF to MET and from SWF to CU

 

[Dave1982]

https://picasaweb.google.com/lh/photo/pvB7PhOrnETMFL7pLarRQZc6fO7wa3BWfpA11pg2i5U?feat=directlink

 

[Dave1982]

looks like TN-S earthing I think. The cable just dissapears in the back of the switched fuse box. To run a new earth would be near impossible i think.
Three flats from this supply.

 

[Dave1982]

the earths are 6mm i would say from main distribution board to second distribution board then to switched fuse and then to CU

 

[Dave1982]

If the tails and earth need upgrading shurely then all the flats in the complex would have to be upgraded...don't see that hapenning. where do i stand? can i go ahead with the work within the flat or not? Anybody had any expearience with this senario?

 

[coxy84]

you must make sure the the exsiting install is safe before under going any additions, you should upgrade main earth and incoming tails.

 

[Dave1982]

Thats fine coxy but the tails are 16mm from the meter which is sealed. so I guess the supplier should do that. The earth may be 6mm from the distribution board to the switched fuse but the cable run from there is Twin and earth (imperial) god knows what size earth on that. The main earth dissapears behind the switched fuse box to god knows wherthen reappears in the back of the CU in the flat.

 

[Dave1982]

Photo of CU in flat just shows the supply cable entering the back of the unit through the gromet.
tails are no longer there as these supplied a separate fuse box no longer required.
https://picasaweb.google.com/lh/photo/_4LWLGGugJ6g7-mRhNQO_5c6fO7wa3BWfpA11pg2i5U?feat=directlink

 

[coxy84]

it sounds like a right pain mate, but you have got to make sure the earthing upgraded before you change the board, there is always a way its just a case of how much it costs.

 

[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