Dodgy wiring setup to shed? Is this a bodge?

[MrJoshua]

Hi all

I've been in my house a few years now and always wondered about the legitimacy of a certain aspect of its wiring, even though there have been no issues as such to speak of while I've been here.

Part of it had been disconnected when I moved in, and I'm assuming it would be a bad idea to connect it back up as I suspect it's a potential bodge, but I wanted to describe it and ask people who know better.

The circuit from my consumer unit that feeds my immersion heater (from a 32amp MCB), has in the past had a double socket added to it in the utility room next to the water tank.
The washing machine and dryer are plugged into this, and we've never had any issues. The immersion heater is never used.

I seem to recall asking the sparkie when we had other work done if this was correct, or if the immersion should have that circuit all to itself and I vaguely recall he said it's not the normal way of doing it but should not pose a problem. I may be remembering incorrectly here but it was all deemed to be fine when we bought the house anyway.

I'm not overly worried about that aspect of it, but my question concerns an apparent previous power feed from this to the shed.

The double socket on this circuit is a spur (I presume as it has a single cable into it) with 2.5mm twin/earth, but it has a disconnected cable from the socket continuing to the shed.
The cable is armoured stuff (black outer rubber insulation then lots of tough steel wires wrapped around an insulated inner sleeve which has black, brown, & grey wires within), and is pretty substantial. This goes down into the concrete path (not sure how deep) for about a metre distance from the house to the shed, then comes up inside the shed to some sockets.

There is a neon spur switch inline inside the utility room, but as I say this feed to the shed is disconnected anyway. Not sure why exactly.

Does this sound like a bodged way of feeding power to the shed? It might be one thing having a double socket in the house on the same circuit as the unused immersion tank, but is it safe that this spur/socket also feeds a socket in the shed or has it likely been disconnected due to being dangerous?

It'd be handy to get power out in the shed and it's obviously had it in the past but I don't want to risk anything if it shouldn't be like this of course. If people end up saying it's actually ok I'll get it checked anyway, but I suspect the answer is "don't hook this up without x y z!".

Sorry that goes on a bit - Appreciate any useful input thanks.
Cheers!
Jim

 

[viewer]

It doesn't sound good, but assuming that you want to restore power to the shed, a few questions need asking to get you started....
Can you work out the size of the cable to the shed?
Does the armoured cable actually go into a backbox with a socket on the front; i.e. was that cable just connected to the socket and sharing the same terminals?
Was there any connection between the armour and the earth terminals?
What happens inside the shed - is that a direct armour to socket connection- and how is that end earthed?
Is there a RCD, and if so where is it (what does it protect)?
Pictures might help.

 

[PrenticeBoyofDerry]

It would be difficult to assess your problems completely, I would suggest having an electrical installation condition report to find out if your system is satisfactory or not!
Ideally immersion would be dedicated circuit, 32a radial and 2.5mm spurs would require investigation!
There could be a good reason why the shed supply has been disconnected!

 

[MrJoshua]

Ta for the quick reply chief!

Re' your questions, in order:
i) The armoured cable I'm almost certain is prysmian steel armoured 2.5mm as I found on B&Q. Looks identical, but I'm pretty sure it's not the 4mm thickness that they have as well.

ii) The armoured cable where it comes in the utility room feeds right in the back of a plastic fused switch with neon, which 'was' fed from the working socket in there. Should there be something else between them?

iii) No, the armour steel wires do not appear to connect to any earth at either end. Should the armour itself be earthed then? I'd have to strip insulation off to do that I guess as it looks like the armour wires stop at the outside of the socket box in the shed and fused switch in the utility room. It's too thick for the whole thing to feed into the boxes I think.

iv) In the shed, the armoured cable goes straight into the double socket box in there. Not sure if that socket is earthed but I can't see any wire coming out that would go to an earth now I've looked closer with a torch. Hard to see but again, I am assuming there ought to be. What's the norm for that sort of thing? Is it something driven into the ground with a wire from the earth terminal in the socket?

v) The only RCD is the one on the consumer unit. There's not any additional ones anywhere. Should there be one inside the shed at some stage?

I've attached a diagram of how it's set up.
View media item 72516
Appreciate the advice thanks. I'm happy enough to do basic stuff as long as I have the correct info as I get my sparkie then to check it's all good once done (mate's brother, and we tend to end up doing favours for each other etc).

It'd be handy to know what's bad about this (sounds like a fair few things!) & needs correcting to avoid taking up too much of his time.
He's very helpful but I don't want to take liberties or he'll drink all the tea in my house!!

One other thing that springs to mind with this potential setup if it's corrected and hooked up, is whether it's likely to cause annoying tripping issues if there is damp in the shed? I don't mean directly where the socket is etc as that's bone dry, but bits of the floor get damp at times and I wondered if it could cause any issues even if it's away from where the wiring is?

Many thanks

*edit* I notice now on further inspection that my boiler is wired into this same 32 amp MCB that the immersion is on. Inside the consumer unit there are 2 load cables coming into the top of the MCB in question so I assume one goes to the boiler direct and the other to the immersion heater and the double socket in there. Could be wrong though.

 

[MrJoshua]

Now I think on it, shouldn't there be a separate smaller sub-unit of some sort fitted inside the shed, with a direct fused connection from the main consumer unit in my garage?

 

[viewer]

You don't need another RCD for safety, but as you say, a problem in the garage would trip the whole house. This may be why the shed was disconnected. To get over this two different types (30/100mS delays) of RCD are needed. Simply putting another 30mS one in the garage might not work as the house one could still trip. In truth with a well designed safe system, nuisance trips are uncommon.

The two wires into the MCB suggest it could be a ring or two radial circuits. This needs checking.

A planned earthing arrangement is needed for the system including the armour. Depending on the distance to the shed, the construction and physical constraints the earth could be exported (i.e. uses the house earthing) or made into TT (a rod at the shed). Earthing of the armour would depend on the system chosen.

The armoured cable should go into a suitable box at each end which gives proper terminals and support. From this box the internal wires or new cable can go to the load.
You don't need a garage consumer unit, but this is often a neat way of separating the shed area from the supply.

Despite your reservations on bothering your friend, I'd suggest getting him to have a quick look and then he can decide on the testing and layout.

 

[MrJoshua]

Thanks very much for the further info - very helpful indeed.

I've no reservations about asking him to look at it, as I'd be doing that as a matter of course with anything like this. I meant more in terms of how much of his time I take up, sorry - I wasn't very clear. In all likeliness I'll just get sparkie to do this since the cable itself is already in place and I'm assuming the other bits would be quick & easy enough for him to do, but since I don't have the knowledge for the intimate details of some of this, I may as well cut to the chase and let him do it.

With these sorts of armoured cables then - due to their thickness, what's the normal sort of protocol for bringing them into something like a socket? I'm just curious about this in respect of if they need 'special' kit designed to suit? I suspect it would fit into a normal metal junction box ok, although it'd have a pretty thin grommet I guess as it's thick stuff. Actually, thinking more it'd need proper glands that earth the armour to the box I'm guessing? Meh, it's all Mac's job to sort what's what anyway when he comes round.

Distance from house to shed is just over 1 metre (1.3 maybe) - so they're right next to each other more or less, just with the concrete path separating them, which the armoured cable goes down into, so I guess it's the case that the normal earth conductor feeding through from the house is ok. But would the armour then need earthing as well, or not. Aside from the task of me getting the sparkie to sort this out, I'm interested in the science behind that particular aspect of it, but it's not at all important as such in terms of getting it done.
I think the main bit of work that will take any time for him is that he'll probably need to feed this cable back directly to the consumer unit in my garage (that's the main house one), since I'm sure it shouldn't be running from a spur like it is now.

I'll talk it all through with him anyway but it's interesting stuff either way, and I appreciate the time taken by people replying, thanks.

Cheers!

 

[viewer]

Yes, the common way is to use a metal box with glands which hold the cable and armour securely then the wires are connected to the circuit. Sizes of glands vary to fit the cable. There are pictures on the TLC website. Some garage units will be made so that armour can be introduced, again via the glands which clamp it, but many are thin plastic which will not take the strain. Space in the unit can also be a problem. Whether the armour is earthed to the box depends on the design of the earthing system. With a TT system it is common to earth at the 'starting' end and then a new earth works from the entry to the shed. Whether this will be your system should be left to the electrician to decide - he will be legally responsible for the design. There are lots of threads on this forum and others about supplies to outbuildings or garages and you'll see lots of different ways of making a safe system; what you can't do is 'pick and mix' from different methods.

 

[MrJoshua]

Thanks for the reply again.

I've picked up suitable glands and metal boxes earlier in the week from B&Q but I haven't fitted either since I'm still not convinced that the source point of this is ok i.e. from the double socket that is a spur.
I'm not a sparkie of course but I had it in my head that you can't/shouldn't use an existing spur to feed something else, and I'm wondering if this is why it was disconnected in the first place.

Don't want to start second guessing about this hence I'm leaving it alone for him to do in due course.

Re' the earth thing - yes, I'll be leaving that to him as well since it sounds like it's not a straightforward thing to decide. What is the science/logic as to why it's bad having more earthing than necessary though?

From what you've said it's not the case that more = better re' earth methods/points and with my lack of knowledge on the matter that seems counter intuitive. Not questioning it in the slightest but it seems strange so I'm interested in why that's the case.

Don't worry if it's a hassle explaining though - I'll do some searching for other such topics as it sounds like it's something covered many times!

Appreciate the input anyway, it's very interesting stuff and I wish I knew more, but it's not something I can dedicate time to learning/training properly on alas.

 

[viewer]

A spur can be taken from a spur if the whole is through a FSU so limiting the total current to 13A. The most important aspect of earthing is to have a low resistance to flow from a fault to earth, so a wire taking fault currents back to the house earth can be better or worse than taking the fault current directly to ground near the shed. This is why the electrician measures and designs rather than assumes. There can be a voltage difference between two safety earthing points separated by a large distance or there can be a voltage difference between a safety earth and something like an earthed satellite dish or cable TV source. This can cause problems with electronics and audio equipment (creating a buzz) and is usually called "ground loop". It also means that a distant shed connected only to the house earth could have a potential difference between the shed electrical circuitry (metal switches or back box connections) and the local ground, so giving a shock risk to anyone standing on the ground and reaching inside to a switch.

 

[MrJoshua]

Ahh, I didn't realise that about the spur thing. It has already got an FSU as shown in the diagram I posted before, so perhaps it's not quite the bodge I initially thought, but I want it to be all correct so I'll leave be until he's free to come down and check it all out.
I might change the socket box in the shed for a metal one and fit a gland at that end (since that'll need doing either way) but will probably leave it all be beyond that.

That all makes perfect sense what you've described about the earthing thanks. I know a little about ground loop & interference etc, but it's interesting to understand more on it.

Appreciate the information thanks very much, I might go and read a little more about that sort of thing, and in the meantime it'll be a text to my mate's brother to tell him the kettle is ready and the good biscuits are waiting for next time he's down our way.....