Inherited shed electrics

[JoeA]

We bought a house with a shed with power. The original setup had two RCD breakers inside the house, and then cables going out to the shed. Then inside the shed there was a rats nest junction box with everything connected up with choc block. One RCD was connected to the shed power (which was to a socket and a light), and also to the pond waterfall pump which was switched via a switch inside the shed. The other RCD was connected to some outdoor lights.

We since have installed a new shed, and completely removed the outdoor lights from the garden. I want to rewire the new shed so that one RCD line connects to the shed power, and the other connects to the pond waterfall pump. I also want to install a proper enclosure in the shed with some form of breakers...but what?

The bare minimum I think is to put a couple of double pole isolators to cover the two RCD circuits, just so I can work on shed and pond pump without worrying about someone playing with the RCDs inside the house. Is it worth adding some MCBs into the mix to separate the shed power socket and shed lights?

 

[Taylortwocities]

Um. I wonder if we have mixed terminology here. These "RCDs" do they have test buttons? What is the spec for them?

its all a bit tough to follow from your description.

Please send pictures, and a wiring schematic. Also tell us what sort of cable is used from the house to the shed and if it is buried, strung from bushes, hung on fences etc.

 

[ban-all-sheds]

Pre-empting a clarification that the devices are MCBs or RCBOs:

I also want to install a proper enclosure in the shed with some form of breakers...but what?

More importantly, why? The most you would need would be an FCU for the lights.

The bare minimum I think is to put a couple of double pole isolators to cover the two RCD circuits, just so I can work on shed and pond pump without worrying about someone playing with the RCDs inside the house.

Double pole switches indoors are always a good idea, as they allow you to isolate an outside circuit if water ingress causes RCD tripping.

But do you really have people there who might play with breakers in your house CU?

If so, how would you stop them playing with the isolators?

What do you do if you need to work on a circuit in the house?

Is it worth adding some MCBs into the mix to separate the shed power socket and shed lights?

The most you would need would be an FCU for the lights.

 

[jg321]

+1 for BAS said.

 

[JoeA]

Sorry I didn't make myself clear. Although it sounds like I'm overthnking it.

These are the RCDs,

They are located on the wall next to the patio doors and I assume are connected to a spur in the ring main. They are in an open location next to a light switch hence my worry about people accidentally pressing them.

 

[flameport]

I want to rewire the new shed so that one RCD line connects to the shed power, and the other connects to the pond waterfall pump. I also want to install a proper enclosure in the shed with some form of breakers...but what?

Nothing. Those RCDs contain fuses, which can be a maximum of 13A. It would be pointless to install any other devices.
Providing the cable connected to them is rated to at least 13A, the cable to the shed can just be connected directly to whatever sockets or other things you have in there.

For isolation, remove the fuses. Optionally put a small padlock through the fuseholder so a fuse cannot be inserted.

 

[JoeA]

OK thanks. So I'm overthinking it.

So there is definitely no mileage in having the shed lights and shed sockets on two separate MCBs inside the shed? It's just lots of articles about wiring sheds seem to suggest this.

 

[Taylortwocities]

Absolutely no point. You have a 13A fuse and an RCD at the house end. So no point for any MCB in the shed. That is all you need for sockets.
Just have an FCU with 3A fuse for shed lights.

Didn’t see a response to this question

tell us what sort of cable is used from the house to the shed and if it is buried, strung from bushes, hung on fences etc.

 

[JoeA]

OK many thanks .

Ah yes, sorry - cable is SWA buried right up to shed.

 

[davelx]

I would want to be able to isolate the sockets whilst keeping the lights working. A 20A DP switch just before the first socket would allow you to do this and you could take the feed to the lighting FCU from the feed side of that switch.

 

[ban-all-sheds]

For isolation, remove the fuses. Optionally put a small padlock through the fuseholder so a fuse cannot be inserted.

Pointless.

Remove the fuse, push the holder back in. In a domestic house environment nobody is going to accidentally go and get a fuse and put it in.

 

[SimonH2]

In a domestic house environment nobody is going to accidentally go and get a fuse and put it in.

That's unlike you BAS - advocating NOT locking off an isolated circuit While I mostly agree with you, there's no accounting for what inquisitive people might do - in some households I wouldn't consider not locking off properly, especially as it only takes a few seconds to do.

 

[ban-all-sheds]

OK, then, remove the fuse, push the holder in, and tighten the screw.

I genuinely, and with utmost seriousness, suggest that at that point, if you genuinely and seriously think that there is a genuine and serious risk of someone inquisitively undoing the screw and inserting a fuse in an FCU which is not supplying anything in the house then you are genuinely and seriously insane.

 

[JoeA]

Are you recommending an FCU for the shed lights simply because in your view it is easier / cheaper?

Presumably even if it was more expensive / more complex, there would be nothing wrong with putting an MCB (of equivalent amps to the fuse in your FCU alternative) on the cable going to a standard light switch?

 

[SimonH2]

Correct. It doesn't matter how you protect the circuit, as long as it's correctly protected. Whether that's a fuse in an FCU, MCB in it's own housing, separate MCB (or RCBO) in the CU, ... Really down to the situation as to what's practical, then what's going to be aesthetically and finally acceptable.