Household Consumer Unit, Extension Leads And Sheds..

[Ads_Essex]

One for all you sparkies and DIYers..

Following on from my post about whether hook-up cables should be armoured or not, it got me thinking about how I trickle-charge my motorbike.

My house is a 50’s build. I’ve been here 8 years and don’t know the history of the wiring, other than they’re the old black and red cables.

The consumer unit / fuse box / RCD looks something like this:


It’s stuffed away behind a cupboard and doesn’t cause any issues - the lights will sometimes dim if loads of devices are running and something hefty like a kettle is switched on - but rarely trips out (it does work, I know that much at least).

Now, firstly - I want permanent power at my shed. Only enough for a light and a trickle charger, and I’ll probably run the lawnmower from there.
What’s the best way to do this - would it want it’s own consumer unit with RCD and MCBs? Or does that then take me in to notifiable territory that will cost a lot of dosh?
The shed is detached and at the side of the house, so if I want to run cable to it, I guess I’ll be burying it.
From the CU to the shed is 28 metres (not as the crow flies, but along a brick wall).


Secondly - should I upgrade this fusebox to something that doesn’t cause the whole house to trip out if and when a fuse blows? Or should I not bother, as it’s not causing me any grief.
If so, how much am I looking at?

I would rather have power permanently installed in the shed but won’t be spending a whole load of money on it just for that sake. If that means bringing the bike battery in to trickle charge it over winter, so be it.

Any advice welcome

 

[Stay Frosty]

Looking at your picture you've got a spare way in your consumers unit so that's a good start, as it's an older board you'll need to look on ebay for a secondhand MCB to suit, you might be lucky and get new so ring your local Edmondsons/Newey & Eyre/Electric Center whoever.
Run a 2 core SWA to your shed and be realistic with the load, if you only want to charge your bike battery or run a lawn mower then a 2 core 2.5mm2 will do providing the shed's not miles away, use 4.00mm2 if it is miles away, that secondhand mcb will be either a 16A or 20A if you use a 4.00mm2 cable.
Looks like your unit is metalclad so that end of the armoured cable can just gland straight in, you'll need two glands for the run and off the top of my head a pair of size BCW20s will do as the shed end will benefit from the glands extra weatherproof seal.
At the shed end of the armoured supply treat the shed as a TT installation and gland off into a PVC adaptable box to lose the wire armouring earth at that point, the two phase conductors live and neutral then carry on through the pvc box into the shed 2 way consumers unit to the main RCD, use a couple of mcbs, a 6A and 16A for a lighting circuit and power circuit.
As a TT installation you'll need to run an earth stake adjacent to the shed to provide a reference earth so that the RCD can see an imbalance should things go pear shaped when using something plugged in, for belt and braces run a bit of 10mm2 6491x earth cable from the sheds unit to the clamp on the earth stake.
This will work safely but the problem you'll get with your house consumers unit having an RCD protecting the whole board is the likelihood of an earth fault detected in the shed tripping the house out despite the house PME earth not being exported, it will happen when you use the test button on the shed consumers unit and it's a ballache that can't be solved easily but is a nuisance that will save lives.
As for testing and will I be able to sleep at night now, this message will self destruct in 3...2...1
It's easy, cheers!

 

[Murdoch]

I would advise against running an external circuit off that board ..... or the shed will be able to trip the house ......

As for TT ing the shed to stop the house tripping ..... that does not work ......

I’m a spark btw

 

[Ads_Essex]

At the minute I’ve got a fused connection unit (13a) indoors supplying a socket that I run an extension lead from. I’m guessing, that unless I’m looking at spending big money, nothing is going to be permanent unless it’s done properly by a sparkie?

 

[Murdoch]

I would start by advising getting that old board replaced, with one with RCBOs

Then go from there

 

[Richard Wood]

Mostly agree with stay frosty, aside from would recommend 4mm 3 core for either 16 or 20 amps based on the 28m you say the shed is from your house board, wouldn't connect the 3rd core at present would just have it for future proofing, like to have an extra earth as well as the amour of the swa, ideally would look at a small board for shed using rcbos, really this should be done by a spark and as your house board is I think obsolete will require a fused isolator in the house as well, at the very least get someone to check it over when your done, are you planning on staying at this house for a while? If so a board upgrade would be a good idea even if only to a dual rcd one, will at least reduce the impact of a trip.
Hope this helps a bit

 

[Murdoch]

Mostly agree with stay frosty, aside from would recommend 4mm 3 core for either 16 or 20 amps based on the 28m you say the shed is from your house board, wouldn't connect the 3rd core at present would just have it for future proofing, like to have an extra earth as well as the amour of the swa, ideally would look at a small board for shed using rcbos, really this should be done by a spark and as your house board is I think obsolete will require a fused isolator in the house as well, at the very least get someone to check it over when your done, are you planning on staying at this house for a while? If so a board upgrade would be a good idea even if only to a dual rcd one, will at least reduce the impact of a trip.
Hope this helps a bit

Whilst a dual rcd board may save a few pennies, it will be wider than a rcbo board, 4 modules to be precise, and that space looks tight already .....

As for getting it “checked over” ..... I never check or sign off diy work .....

 

[Richard Wood]

Agree a rcbo board is by far the best but not everyone has the funds and at least a dual rcd would be an improvement, linked main switch, metal board etc, checking work of others is a tricky area but in this instance as long as could see cable buried to correct depth and in one piece, both ends are easily accessible I personally wouldn't have an issue with, to my mind no worse than doing eicr on a property that has no history

 

[Murdoch]

As I said, that picture suggests there isn’t room ......

As for DIYers or builder bodgers....... they can’t test, inspect, sign off or notify and undercut the people which the competence and knowledge .... there’s no tricky area

 

[Stay Frosty]

Sparky here too FWIW and realistically the shed has to be TTed as you can't export the earth from the house if it's TNCS or TNS as in the photo.

I pointed out that the shed RCD will trip the house RCD both being 30mA devices, that's actually good, a work around could be to use an S type time delay RCD at the house end but that would need Henley blocks and RWs sw/fuse at the house mains meaning cutting into the existing tails before the consumers unit.... basically a ballache and meaning getting in a Sparky to perform the task and subsequent cost escalation.

OT but testing is a tricky area and realistically for an EIC unless you're only testing work on a fairly modest scale completed by yourself then you have little idea of what's going on in the parts of an installation you can't see, as the qualifying engineer on a larger job you could be signing off on all sorts of cack work that give the right R1R2, ZS and insulation resistance etc. so must be OK right?

At Ads you could add a bit of protection to the existing lead by running it through some flexible conduit, they do clips too so the conduit could then be fixed to say the wall at low or high level where it would be visible but a bit more mechanically protected.

Polypropylene Flexible Conduit 25mm x 50m Coil Black

Cheapest option though would be to unplug the lead when not in use.

 

[Murdoch]

Sparky here too FWIW and realistically the shed has to be TTed as you can't export the earth from the house if it's TNCS or TNS as in the photo.

Yes you can export the earth on both of those ....

 

[Stay Frosty]

I say not to a shed 28m away from the houses equipotential zone and in this particular case you're exporting the earth provided by that EC15 earth clamp shoved on the incoming cable sheath.
Going further and really the whole house should be on a TT install to guarantee disconnection times as that clamp can't be counted as being provided by the local DNO.