New build SubMain

[dhb368]

I am currently undergoing a self build and have a temporary CU serving a mobile home. The service is/will be TT

I have arranged for the main supply to be moved into the house, but will require power to the existing temporary CU until the house is finished.

I have been advised that in the house I need to install 2 sets of meter tails 1x CU and 1 for a switchfuse which will connect to the submain.

A few q's

1. Will I need to supply/install a meter connector block for the 2 sets of tails or will the supply company do that?

2. I only need a 20A supply to the submain, but allow for 32A, which will be 12m away. I am using 4mm SWA. The mains supply will be 100A. What rating would I need for the switchfuse.? 32A?
Should it be a double pole switch as I would need to be able to isolate the SubMain supply?
Should I have an RCD on this switchfuse?

I was thinking of either

http://www.qvsdirect.com/Wylex-60A-Metal-Clad-Switchfuse-S.P.-pr-16901.html which is single pole or

http://www.qvsdirect.com/Excel-80A-Fused-Double-Pole-Main-Switch-pr-22561.html which was my prefered choice as it is double pole.

Or could I use a a small CU with a 100A mainswitch and a 32a RCBO as the switchfuse?


3. An electrician told me that I could just connect the SubMain to an MCB on the main new CU, and therefore not need the switchfuse at all. Any opinions?


As a seperate issue I will be doing the basic work myself and need to find a Part P qualified to certify at the end. I am just west of Cambridge. The guys I have spoken to say that they can only certify their own work. Any suggestions?

Thanks[/b]

 

[ericmark]

If you are under local authority building control already then so long as you have included the electrical work they will be responsible for inspecting and testing. It can be sub-contracted to another electrician by them but not by you to do inspection and testing.

It is normal to have the electrical supply arranged so it can be isolated by a single isolator. In my area the supply authority often provide that but yours may be different. Because under electricity at work act one must isolate elsewhere before working on a board it is better not to have the main isolator as the one built into the consumer unit especially with a TT system as neutral is considered as a live so removing the fuse is not enough.

Although this is technically what is required many electricians still wire houses and rely on the isolator in the consumer unit as main isolator. However much would depend on the designer. For example using a 300ma RCD in its own box as the main isolator may have some real advantages allowing you to modify your system in the future without needing to get supply authority to do isolation.

However to design and install an electrical system does take a lot of know how and unless one is in the trade it is likely you will make mistakes and the LABC I would hope would require you to submit your plans so errors could be highlighted before you start. But I know from my son the LABC where he has had dealing with have just taken the money and inspected on completion if they would have acted different if he was not qualified I do not know but since charge was the same they should have done same checks and he did not submit plans which to me is wrong.

If using a consumer unit with a 300ma RCD as main switch and 30ma RCBO's as circuit protection for sockets bathroom and outdoors at first glance it may seem better to supply the mobile home from a RBCO but you may find the mobile home comes under same rules as a caravan and it may need a RCD which also switches neutral. So really speaking without being on site and seeing exactly how it is all set up it is all too easy to make mistakes.

So I would advise you get a local electrician to draw up the plans so no mistakes are made.