Rewire Plans

R

ryanj

As I have a week off work soon, I am going to, after a long delay, rewire the house. I can do this myself and own most and have access to the rest of the necessary calibrated testing equipment. I own a brand-new Megger, an Earth-fault loop impedance tester and I also own various multimeters. And I can borrow a RCD tester from a friend. I own all the guidance notes, the on-site guide and a copy of the regulations.

I live in a single story house, but it has recently had a loft extension, giving us a third bedroom. Downstairs, there is a kitchen, dining room, living room, bathroom, hall and two bedrooms. There is also a pantry in the kitchen and a porch before the front door. The external walls of the house are of some sort of cavity. Their is also a shed, less than 10 metres from the back of the property.

The existing installation is on the back wall of the porch in the kitchen, it consists of three individual sheets of chipboard. They are spaced of the wall with ceramic spacers attached to battens screwed into the plasterboard. The first sheet of chipboard contains the main fuse and the meter, the second, the main consumer unit and the third, the second consumer unit (previously an Economy 7 consumer unit) and a RCD.

The consumer units are old Wylex 6way fuseboxes, and the RCD and meter are rated at 80amps, while the main fuse is at 100amps. The installation is TT, supplied from three phase overhead lines, with a two cable drop to my my semi-detached house. The house next door also shares this drop. A 16mm² cable leaves the main consumer unit, out the wall, down a conduit and straight into the tarmac. I presume the earth rod is also under the tarmac. The second consumer unit is earthed via a loop of 16mm² cable between the consumer units.

The existing circuits are pretty badly designed and have been changed over the years, there is two very uneven loaded lighting circuits, 5 single socket circuits (caused by removal of storage heaters), an immersion circuit, one ring main covering the whole house and an cooker circuit. Recently a shower has been added, and a plug-in 40amp MCB has been provided.

The cables from the drop to the cut-out and from the cut-out to the meter are 35mm² black and double insulated. From there 25mm² cable to the RCD, and two lots of 16mm² cables run to the seperate consumer units. The main equipotentiol bonding conductors are almost non-existant. The bond to the water consists of a 2.5mm2 bare cable running from the consumer unit and then wrapped around the water pipe. And the main 10mm² bond to the gas is at the boiler, rather an 600mm from the pipes entrance to the house.

All the lighting is in badly installed threaded conduit. There is no covers on the junctions, and I doubt the conduit is connected to earth at all. The rest of the wiring consists of modern twin and earth and old rubber insulated twin and earth.

Here is a picture of the installation:-

oldintake.jpg


I plan to replace everything there with a single sheet of 12mm thick Medium Density Fibreboard (MDF), spaced of the wall using ceramic spacers of new battens. The cables will leave the consumer unit through a hole in the back of the MDF and then through a hole in the plasterboard, and then up into the loft void. No cables can travel downwards, because of the kitchen's concrete floor.

ScottishPower are willing to replace the drop to the house, upgrade the supply to TN-C-S (PME) and move the service head and meter within 2 metres of it's current location for £250.

Here is a plan of what I hope to acheive:-

newintake.jpg


The cables leaving the bottom of the board, the service entrance and water and gas main equipotentiol bonds will simply enter the cavity hidden behind the board. The main bonds are in 16mm² and join at a simple 4-way earthing terminal. A 16mm² cable also runs from the cut-out to the block and the consumer unit to the block. Their will be a two module MK enclosure housing a simple double pole isolator between the meter and the consumer unit.

The consumer unit is a 16-way MK Sentry. The first two ways will simply have another double pole isolator. Instead of any RCD's, I've opted for RCBO's for convience incase of any tripping.

I propose to install the following circuits:-

circuitchart.png


But, I'm a little bit concered with my splitting of my sockets simply into upstairs and downstairs, due to their only being one bedroom upstairs. The lighting will be quite random, simply two circuits providing half of the loads each. The doorbell, shaver socket and extractor fans are also to be ran from these circuits.

I simply wanted to know if my circuits are up to scratch, or if there are any problems I might encounter with their layout. I would also like to hear peoples comments on the new intake board before I touch anything, and call ScottishPower to move their stuff.

Phew. Thanks.
 
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B

breezer

I get a feeling scottish power will not move their stuff. Its late and time for bed
 
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breezer said:
I get a feeling scottish power will not move their stuff. Its late and time for bed

ryanj said:
ScottishPower are willing to replace the drop to the house, upgrade the supply to TN-C-S (PME) and move the service head and meter within 2 metres of it's current location for £250.
 
R

ryanj

I haven't ever had any problems with ScottishPower. They were very helpful when we got the storage heating removed.

Any replys? ;)
 
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If there is just one room upstairs I would possibly not bother having an upstairs ring, logically speaking makes sense but might not be worth it with kitchen / utility area allready being seperate.. Suppose you might as well though.

Only point I can pick holes in is the boiler, I would use a 16a and a FCU via 2.5mm t&e

David
 
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I think that was a joke, about scottish power not doing the work today.

Longest most detailed post i've ever seen. Perhpas a little too detailed for everyont to spend 20 minutes reading it before answering questions.

Is it your intentions to remove the 80A, presumably 100mA, existing RCD once the supply earthing has been upgraded? or to hang on to it as additional protection to non rcbo circuits? It does represent a theoretical limit point of 80A on the amount of current you should draw, without any way of limiting the current to 80A.
 
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why al the RCBO's? why not a split load CU?
 
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It would be pointless on the lighting circuits or any which would be on the non-RCD side of a normal split, but using RCBO is technically better as a fault does not switch off unaffected circuits. Depends if the cost is worth it to you. If you are doing the work yourself, maybe some of the money saved can be spent on this instead.
 
R

ryanj

Only point I can pick holes in is the boiler, I would use a 16a and a FCU via 2.5mm t&e

I had actually thought about doing that, the boiler part is actually already been rewired in 1.5mm², it would be very little inconvience to upgrade it to 2.5mm². What are the reasons for the 16amp MCB?

Is it your intentions to remove the 80A, presumably 100mA, existing RCD once the supply earthing has been upgraded? or to hang on to it as additional protection to non rcbo circuits? It does represent a theoretical limit point of 80A on the amount of current you should draw, without any way of limiting the current to 80A.

I am going to remove the 100mA 80amp RCD once ScottishPower have been round. The whole idea was to keep everything pretty simple, and each circuit having it's own overload and earth-fault protection if required.

why al the RCBO's? why not a split load CU?

I'm not a fan of those split-load boards. Eugh ;). I like RCBO's, a simple little unit not to much bigger than a standard MCB, keeps the wiring simple, and it'll be more convient incase there ever was to be a trip.
 

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