Electricity to Garage and Pond - Advice Please

[Martin Cook]

I'm looking for some advice on how to improve the design of the electrical wiring I've inherited from the previous owners of my house. The issue of concern lies with the supply to the detached garage and pond (2 pumps and a UV clarifier).

Last winter one of the O-rings in the UV clarifier failed whilst we were away and let water into the electrics, this of course tripped the RCBO on the circuit. The problem is that the garage and the pond equipment are supplied by a fused spur from the downstairs ring-main, so it was goodbye to the contents of the fridge-freezer and a some programmes scheduled to be recorded on the Sky+ box.

Rather than just regularly replacing o-rings and the pond equipment and crossing my fingers I want to find a way of stopping this happening again. I think the obvious solution is to put all the garage and pond wiring on an independent circuit fed from the consumer unit in the house but the consumer unit looks to be at full capacity so presumably I would need to replace this alltogether and start again as well as redoing much of the external wiring. This sounds to me like an expensive and complex job probably requiring a professional.

The only other option I can think of is replacing the fuse unit in the fused spur to the garage with an RCD version but I'm presuming this will not guarantee the the whole ring main won't still trip out if there is a fault.

Any advice welcome.

Martin Cook

[Lurch]

On Sun, 21 Nov 2004 22:08:54 +0000 (UTC), "Martin Cook" strung together this:

I would be looking at getting a dedicated supply down to the garage and pond. If the existing CU is full then as you only need a 13A supply I would remove one of the lower powered circuits from the existing consumer unit on the non-RCD side. Use this circuit, (with a 32A MCB fitted to it), to run a 6mm cable to a 2 way consumer unit with main switch incomer next to the existing one. Populate this 2 way CU with a MCB rated for the circuit you just removed and a 16A RCBO for the outside circuit. If 16A is over-rated for the cable that is running outside then fit a switched fused spur between the RCBO and the supply going outside. The other alternative is to fit an RCD onto an existing non-RCD'd circuit to feed the outside. The above assumes you have a split load consumer unit, if it is one RCD supplying the whole installation then you're going to have to change it or add another consumer unit with RCD for the outside circuit, wired into a Henley block between the existing CU and meter position.

[PhilÃÂ]

Martin Connect it to your nearest lamp post, then if it happens again you will not be affected.

[John Southern]

Street lighting columns are actually fused with BS88 fuses. The REC install a fused cutout or they are private supply from a feeder pilliar in which case they have an isolator fitted.

Jon.

[Lurch]

On 22 Nov 2004 10:07:53 -0800, [e-mail] (John Southern) strung together this:

Well, that depends if they've got a BS88 fuse in them.....

Not quite sure what the anoraky bit was for, but still.

[Martin Cook]

Thanks. This is a great help.

I have had a look again at my Consumer Unit. Its a Crabtree Starbreaker (1995 vintage) with a capacity of ten modules, nine are in use.

It is laid out as follows, left to right:

1/2 Main switch (100A) - occupies 2 modules. 3 MCB B32 - Cooker 4 RCBO B32 - Downstairs Ring Main + Garage/Pond Spur 5 30mA Device (trips RCBO32 when test button pressed) 6 MCB B32 - Upstairs Ring Main 7 MCB B16 - Central Heating 8 MCB B6 - Downstairs Lighting Circuit 9 MCB B6 - Upstairs Lighting Circuit 10 Blanking Plate

Martin

[Andy Wade]

I shall assume that 4 and 5 are a single device - the 32A/30mA RCBO - and that all the other circuits have no RCD protection.

That being the case you could install a suitably-rated MCB in position

10 (hopefully the busbar finger won't have been cut off) to feed your new outdoor circuit. Then provide 30mA RCD protection somewhere downstream - e.g. in a separate 2-module enclosure adjacent to the CU, or by means of an 'RCD spur' unit elsewhere.

[Owain]

"Andy Wade" wrote | Martin Cook wrote: | > I have had a look again at my Consumer Unit. Its a Crabtree | > Starbreaker (1995 vintage) with a capacity of ten modules, | > nine are in use. | > It is laid out as follows, left to right: | > 1/2 Main switch (100A) - occupies 2 modules. | > 3 MCB B32 - Cooker | > 4 RCBO B32 - Downstairs Ring Main + Garage/Pond Spur | > 5 30mA Device (trips RCBO32 when test button pressed) | > 6 MCB B32 - Upstairs Ring Main | > 7 MCB B16 - Central Heating | > 8 MCB B6 - Downstairs Lighting Circuit | > 9 MCB B6 - Upstairs Lighting Circuit | > 10 Blanking Plate | I shall assume that 4 and 5 are a single device - the 32A/30mA RCBO - | and that all the other circuits have no RCD protection. | That being the case you could install a suitably-rated MCB in position | 10 (hopefully the busbar finger won't have been cut off) to feed your | new outdoor circuit.

If position 10 is unavailable then provided the central heating on No7 is only a pump and controls (i.e. NOT immersion heater as well) you could wire it through a FCU fused at 3A and and supply the FCU from one of the power rings. Label the FCU clearly as "CH from xx ring". You could then use the No7 16A MCB for your outdoor circuit, through an RCD somewhere external to the CU.

Owain

[John Southern]

Well i can imagine some t**t breaking a door off to connect into a column and getting a nice whack from the board cutout. Ive know people to run xmas lighting from columns just wiried into the lantern.

Jon.

[Lurch]

On Tue, 23 Nov 2004 14:19:09 -0000, "Owain" strung together this:

Rather than any one, use the upstairs ring as this isn't covered by an RCBO. That way the heating will still work if there is an earth fault on the downstairs ring.

[Owain]

"Lurch" wrote | >If position 10 is unavailable then provided the central heating on | >No7 is only a pump and controls (i.e. NOT immersion heater as well) | >you could wire it through a FCU fused at 3A and and supply the FCU | >from one of the power rings. | Rather than any one, use the upstairs ring as this isn't covered by | an RCBO. That way the heating will still work if there is an earth | fault on the downstairs ring.

I did think that, more from the opposite POV of a minor earth leak on the heating not taking out an RCD protected ring.

Owain

[Martin Cook]

Thanks to everyone for the helpful advice. It looks like I have at least a couple of good options to go forward with and none of them are as radical as I had feared!

Martin

[Lurch]

On Tue, 23 Nov 2004 09:11:29 +0000, Andy Wade strung together this:

No finger, the old Crabtree ones were the screw on type, the screw fitted into a recess rather than a finger fitting under a screw. Minor technicality I know!

I think this would be what I would do if I were called in to do the job. Easiest solution all round, from a materials and labour point of view, and it's effective.