main suply..

[kuksiani]

maybe im not in right place for asking..but anyway..i have one problem and i like to discusswith any one who its expert for electrician design..

i have to fix one metter room for about 15 flats..i fix rayfiel board , switch for 15 flats ,electric metter.etc ...when i ask EDF to provide suply i was supprised..one EDF man come to metter room and ask me '' how many amps you need for suply..'' i was supprised because i thot he can calculate that..hi going whith no any advice...the problem its that im qualified electrician but im not electrician design ..second problem its that the person who do wiring all 15 flats its just skilled person and not consulted with any architect..i dont know what to du..im asking here any one who can show me way how to calculate this..how can i find AMPERS for one flat and how can i find AMPERS for 10 , 15, or more flats..i want to know that not just for this job but i want to know for my skills..maybe i have same problem on the future ..please if any one know any webpage who can help me let bring here..or any thing who can help just bring here..

 

[Guest123]

You need to carry out a maximum demand calculation, taking diversity into account.

There are a number of books that can help you.....

https://www.amazon.co.uk/Electrical...5504/ref=sr_1_1?ie=UTF8&qid=1287228451&sr=8-1

https://www.amazon.co.uk/IEE--site-...=sr_1_1?s=books&ie=UTF8&qid=1287228477&sr=1-1

 

[malcolmsanford]

Have you any responsibilty with the 15 flats and if you have do you, or do you want to know about Part P of the regualations?

The DNO willl want the loading on each flat to work out the type of supply you want, as it is 15 flats the chances are it will be a 3 phase supply, but they will not know this until you give them your loads.

As you say if you are qualified then you should be able to work out all your calcs for the loading with the diversities involved. You will also need to factor in your erection methods for running the submains to each flat.

What type of earthing system are the DNO proposing for you TNC-S or TN-S. If not will you be TT'ing the system. All this will effect your design criteria, but as a fully qualified electrcian you will know this

 

[kuksiani]

thank you lenny..

 

[kuksiani]

Have you any responsibilty with the 15 flats and if you have do you, or do you want to know about Part P of the regualations?

The DNO willl want the loading on each flat to work out the type of supply you want, as it is 15 flats the chances are it will be a 3 phase supply, but they will not know this until you give them your loads.

As you say if you are qualified then you should be able to work out all your calcs for the loading with the diversities involved. You will also need to factor in your erection methods for running the submains to each flat.

What type of earthing system are the DNO proposing for you TNC-S or TN-S. If not will you be TT'ing the system. All this will effect your design criteria, but as a fully qualified electrcian you will know this

thank you malcolm..

i dont have any responsibility with 15 flats wiring..just to do metter room and main suply..but realy i want to know that what i ask..i have level 2 on 2330 and 17th edition but realy i newer do calculate for loading..i know for individual circuit but not for all flats or block of flats..
DNO proposign TNC-S earthing system 3 phase suply..and no more information..i thot its any one here who can explain step by step all formula for one flat and for block of flats..
anyway thank you for your advice..

 

[malcolmsanford]

You will have to speak to whoever is doing the flats as he will have the information on what loads each flat will require.

So who is running the sub main from the meters to each flat? You or him?

In some sense your trying to prepare a meal but don't know how many people are coming and so therefore how much ingredients are needed. Unless you know what each flat power/loading requriements are you can't calc your main supply.

Also you will need to most likely have a partial Intitial Verification for each flat, and the sub mains for the DNO to connect the supply, so you will have to liase with whoever is wiring the flat to get connected.

 

[kuksiani]

malcolm
the person who do flats wiring dont have qualification..i have see all flats instalation ..he running 16 mm2 SWA cable from the meter to the flats..and i think its correct size of cable.the maximum distance from consumer units to the meter room its 12 m...block of flats have 1,2,or 3 bedroom..in each flats have 1 cooker circuit with 32 amp mcb , 1 boiler 16A MCB,1 main ring with 32 A mcb , kitchen ring 32A mcb , 2 light cirkuit 6A each one..i thot its correct instalation comply with 17th edition..i have fixt 63A swict on meter room for each flats because main cable its 16 mm2...i dont know what to say more...

 

[malcolmsanford]

Well the DNO as a rule of thumb of adding the protection device and divide by 0.4 so you would have 32+16+32+32+6+6 = 124 x 0.4 = 49.6amps so your 63 amps should be ok.

!6mm^ SWA on that load, with that run should be ample. Is the SWA 3 core or 2 core? Is the SWA burries or surface as this will decide if you need to RCD protect it or not.

 

[kuksiani]

its 3 core cable and its mechanically protected..no need rsd protectet for them..ok now we know maximum demand for one flats..and let say all flats have same maximum demand..how can we find for 15 flats..or more or les than 15

you mean 49.6 amps its maximim demand for one flat ??..

 

[malcolmsanford]

No that is the demand with diversity factored in. You therefore will fit a 63amp MCB protection device or a 60amp Fuse, I would choose fuse. Your protection device is then protecting that 16mm^ SWA.

You are saying as designer that with the circuits installed and then diversity applied your are supplying a 63 or 60 amp supply for that load. If you feel that a bigger load is required then as the designer you are entitled to do that. Your 16mm^ Armoured depending on erection method can be rated from 78amps to 89amps with a short 12 metre run.

But by using diversity you can keep costs down and design proper installations otherwise in these days a normal house with showers and cookers, ring final circuits etc can take a maximum load in excess of 150amps without diversity, and so ridiculous size cables and protection devices would be needed.

 

[kuksiani]

dont complicate malcolm..can you calculate maximum demand for one normal flats ( not house ) and for group of flats..just simple way..

 

[malcolmsanford]

Define normal please ..........................

Ok last one and here it is. You have a 16mm^ cable installed by the other electrician or whoever he is. So now your governed by that so regardless of what the flat wants it is only going to get at a maximum on erection method A 89 amps. Now if your erection method is D then your going to get only 78 amps. So you can work that out.

If it's A then fit a 80amp BS 1361 type II fuse, if it is method D then a 60amp BS 1361 Type II fuse. System designed