3xflat rewires

[bartkusal]

Hello everyone,
I need some light on some issues ,and hope you guys can help me,I'll try to be short...
This afternoon i am going to have a look at three flats which needs a rewire, and potentialy start next week, so I need to grasp a couple of things before I get there. It is council flats,everything is ready to be started, they want all circuits surface mounted ( I know horible,not my cup of tee, but thats what they want, and I have no intentions to argue,in fact it only will be easier for me).
I have to say the job will be used for my assesment with NIC, so no mistakes here. I have extencive experience with house rewires for the company and cormftable with everything, but I start on my own and I never done flats, especialy council ones. So potentialy I hope you can advice what to expect from the job, and what assesor may be picky on.
The main thing which concerns me is the main incoming supply. I know by the latest regs we have to install minimum 25mm2 meter tails, 16mm2 main earthing and 10mm2 main protective bonding to water and gas. What I am trying to make sence of is, if the supply cable to meter have only 16mm2, so what is the point to increase it to 25mm2 after meter, its not like the supply cable is to small for the load, and dont realy need increasing for this mater, but I cant find enywhere in the regs is there is a requiment for it to be 25mm2, and if there is, who is responcible, I suppose its not DNO as the suply will end at the main cutout in the basement and feed to flats are just submains distribution circuits, so if there is the requirements to change to 25mm2, who has to do it, and how to go about it.
Aswell as this, if you have any issues I should be aware of, please let me know.
I am very gratfull in advance for your time and advice, most apreciated.

regards: Al

 

[kingeri]

The tails don't have to be 25mm. What is the size of the main cutout fuse?

 

[simpson93]

No it is a recommendation that you change the to 25mm tails, but at the end of the day the size of the distributor fuse or in your case the main intake fuse will denote the size of your tails. As this seems to be a flat I would guess that there is little chance you will ever need a fuse larger then 60amp.

 

[buttonmoon]

The first thing I would do is estimate the maximum demand for the installation taking in to consideration possible use of electric heating, showers, cooker, etc. and then if that comes to less than 60A then 16mm should suffice depending on the length and any other cable factors involved. The rule of thumb is a 60A fuse will protect a 16mm cable and a 100A will protect a 25mm cable.

 

[Guest111]

The only other thing to bear in mind is if the client wants 25mm tails for their own spec,our local housing association specify that all showers must be installed using a 10mm cable,as this will not be damaged should anyone install a bigger shower later,may be the same with tails.In the past I,ve worked for firms who only use 25mm tails,but as said above as a general rule of thumb if a 60a service fuse then 16mm tails if 80 or 100a then 25mm tails.

 

[buttonmoon]

I agree

 

[lockhes]

Run that's my advice lol

Just started doing council work and hate it our council want 2 doubles in each bedroom 3 in living room 8 points in kitchen 6mm cooker 10mm shower smokes etc

Only done 1 flat so far and hated it just looked horrible been surface this was supplied with 16mm split con and they were happy to leave that in but the houses we use 25mm tails

Hope that helps

 

[bartkusal]

The first thing I would do is estimate the maximum demand for the installation taking in to consideration possible use of electric heating, showers, cooker, etc. and then if that comes to less than 60A then 16mm should suffice depending on the length and any other cable factors involved. The rule of thumb is a 60A fuse will protect a 16mm cable and a 100A will protect a 25mm cable.

Thank you very much for your replies. Yes, max demand is lower than 60A, no question, the heating is gas so just feed for boiler spur, no electric showers, for coocker just oven electric 3kW, the hob is gas,extractor fan,1 ring maybe 2, 1 lighting circuit maybe 2,tbasicly you looking at 45A max.
The cut out in the basement is 60A ( I been told, there was no access at that instance and looking at 16 cable I presumed it is), supply to meter from cut out is in 16mm2, earthing 10mm2. It seems that tails are recomendations, cos i cant find enything in regs just in OSG mentions being 25mm2 minimum but it is just a guide, but earthing conductor to MET has to be 16mm2 as per table 54.7 in BGB. So it must be changed, so the question is still here, who has to change it, normaly I dont touch enything before meter, it is not to DNO either as far as I understand, cos it is sub main, I presume it has to be responsability of the housing association,for whoom works the builder and I work for him, so it can come back to me again, not looking forward to this. What is your thoughts..
I gave builder the quate for all 3 flats,up to flats meter only, 2x 3 bedroom and 1x 2 bedroom,mk materials, 2 zone fire alarm systems in all , labour. All for £4850

Again, all you replies most apreciated.

Best reagards: Al

 

[buttonmoon]

I don't think it does have to be 16mm. Assuming that there is some main bonding present then it has to be at least 10mm but table 54.7 can be overruled by using the adiabatic equation (Somewhere in BRB)which normally results in a considerably lower csa.

 

[bartkusal]

I don't think it does have to be 16mm. Assuming that there is some main bonding present then it has to be at least 10mm but table 54.7 can be overruled by using the adiabatic equation (Somewhere in BRB)which normally results in a considerably lower csa.

Still trying to get at the bottom of this, Can I realy leave the 10mm2 supplies earthing conductor to the flat alone, if the adiabatic equation prooves its adequate. And is this ok for both TN-S and TN-C-S? I still need to see the main intake for the building regards confirming fuse size as 60A, what supply we have TN-S or TN-C-S, and see where that earthing conductor is terminated, cos it is seperate single core cable.
Thanks again for advice...

 

[Engineer54]

Surface domestic installations are not ideal by anyone's standards, but they can be made to look professionally installed. It almost invariably comes down to the installation and fabrication skills of the electrician installing it, whether the finished installation looks like a pig's ear or not....

 

[bartkusal]

Surface domestic installations are not ideal by anyone's standards, but they can be made to look professionally installed. It almost invariably comes down to the installation and fabrication skills of the electrician installing it, whether the finished installation looks like a pig's ear or not....

Hi E54 . I know what u saying, but as I said it is a council flats and thats what they want and I with all my pride will try to do my best for the trunking work to look like an art work, do you have any comments on the questions I had? That would be most apresiated. thanks

 

[Engineer54]

Hi E54 . I know what u saying, but as I said it is a council flats and thats what they want and I with all my pride will try to do my best for the trunking work to look like an art work, do you have any comments on the questions I had? That would be most apresiated. thanks

I would simply go by the DNO fuse rating of the installation, 16mm tails are more than adequate for a 60A supply, 25mm tails being pointless at this time (and for a good time to come) for a typical 2 bed flat, with or without electric shower......
So 16 and 10 theoretically is fine. But then, that doesn't take into consideration the distances and other de-rating factors involved between the service cut out and your flats. What story are your flats on, and what sort of distance's are we talking about??

 

[bartkusal]

I would simply go by the DNO fuse rating of the installation, 16mm tails are more than adequate for a 60A supply, 25mm tails being pointless at this time (and for a good time to come) for a typical 2 bed flat, with or without electric shower......
So 16 and 10 theoretically is fine. But then, that doesn't take into consideration the distances and other de-rating factors involved between the service cut out and your flats. What story are your flats on, and what sort of distance's are we talking about??

Tne flat is on the gr fl. the other two on the 3rd loor, shouldnt be more than 30-40m for the longest runs, method of instalation of supply cables is in 32mm metal conduit buried in the walls/paster, not in insulation, conduit is not shared i with other circuit at the end of the run, but most probably they meet somewhere in the trunking at the begining of the run with supply cables to other flats, so it would be bunched I suppose.
Once again , thanks for replies...