Conservatory power and lighting from existing FCU

[1974stephen]

We are going to have a conservatory built and I have a query regarding the power requirements.

There is an existing FCU in the kitchen that is part of the downstairs ring main that feeds and outisde waterproof socket (RCD protected). This socket will be inside the conservatory once it is built.

Can this socket be removed and the FCCU used to power some sockets and lighting points in the new conservatory without having to get Part P certification or pass any other red tape issues? I am unsure as to whether altering the characterisitics of the circuit includes changes on the load side of the FCU.

Thanks in advance.

 

[festa]

As long as the Zs reading at the furthest point in your soon to be extended circuit does`nt excede the value stated for the mcb/fuse which is protecting the original circuit that your fcu is on, in BS7671 then there is no reason why you can`t do what you plan to do.
You could always play it safe and replace the standard FCU with an FCU with integeral RCD protection.

 

[ColJack]

surely a conservatory needs planning permission?

the electrical work would be submitted as part of the overall planning..?

and yes you can use the load side of the FCU to run a few sockets and lights in the conservatory. ( note you will obviously then be limited to 13A max on in the conservatory )

as it's "2. Work which -

(a) is not in a kitchen, or a special location,

(b) does not involve work on a special installation, and

(c) consists of -

(i) adding light fittings and switches to an existing circuit;

(ii) adding socket outlets and fused spurs to an existing ring or radial circuit; or

(iii) installing or upgrading main or supplementary equipotential bonding."

then I don't think that you need submit a building notice..

unless you intend to provide a new outdoor socket on the exterior wall of the consevatory..

of course the new part of the installation will have to comply with the 17th edition re: RCD protection of cables buried less than 50mm deep in a wall, but presumably it already would be since it's a downstairs power circuit and has an outdoor socket on it..

if not, then one method of coplying is to change the FCU to an RCD FCU, this ensures the new cabling is protected.. but not the old..

 

[GaryMo]

As long as the Zs reading at the furthest point in your soon to be extended circuit does`nt excede the value stated for the mcb/fuse which is protecting the original circuit that your fcu is on,

That would only apply to the supply terminals. The load side circuit (at the furthest point) will take it's maximum Zs figure from the inserted BS1362 fuse in the FCU.

 

[festa]

Very true Gary ...If the FCU was replaced with one with integral RCD.
However if the op just extended the circuit from a standard FCU then any earth faults would zip past the BS1362, as they will only pick up over currents or shorts .

 

[festa]

*OVERLOADS or shorts

 

[ColJack]

but that's the point..
the Zs takes into account the Ze earth path..

so as long as the Zs is low enough to cause operation of the fuse in the desired time, then it complies ( with that part of the regs anyway.. )

 

[GaryMo]

Are you saying that a BS1362 fuse won't blow under earth fault conditions?

e.g. A BS3036 semi-enclosed fuse protecting a ring final including a FCU.
A fault of 210A or above will disconnect the fuse in the required 0.4s.

The 13A BS1362 cartridge fuse would only require 95A to disconnect in 0.4s.

 

[festa]

I get you now....

 

[festa]

Gary .....how did you get to that figure of 95A ? where should i be looking?

 

[GaryMo]

Gary .....how did you get to that figure of 95A ? where should i be looking?

Max Zs for a 13A BS1362 fuse is 2.42ohms (table 41.2 (d))

I=V/R

230/2.42 = 95.04A

 

[ColJack]

don't know the exact page, my regs book is at work, but it's the logarythmic graphs in the appendecies..

although, in my 16th book that i've got with me, there is no chart for 1362's, only 1361's ....

 

[GaryMo]

Same with the 17th Col, hence the calculation.

 

[ColJack]

I noticed in the 17th, they omitted the max Zs for a 5A 1362 fuse... do they not recognise that as an available size anymore?

nevermind, just looked in my 16th and they only listed the 13A in there, so we got one more in the 17th....

 

[Spark123]

You can always look at the manufacturers data for them, the bussmann datasheet is available here: http://www.farnell.com/datasheets/55950.pdf