New Build Wiring

[bluebird01]

Hi peeps

i have built a outhouse at the end of my garden and need some electrical advice . i wish to install 8 sockets and 3 wall lights. The sockets will be powering 1 television, 2 x 2kw rads, 1 x 9kw water heater, 1 x 400w macerator and i would like 2 spare sockets. My consumer unit in the house has 2 spare sockets. i have bought the sockets, lights, consumer unit (6amp & 32 amp mcb's with rcd) and a lenght of 10mm twin & earth. My questions are:
a) is this do-able for someone with no electrical knowledge ?
b) does the set-up sound ok ?

 

[DESL]

a) is this do-able for someone with no electrical knowledge ?

Possibly but ill advised. I guess you could dig the trench for the cable.

b) does the set-up sound ok ?

Depends what you think you will be doing with 10mm2 twin & earth

 

[rockdg]

Hi
If you have to ask the question in the first place then the answer is NO!!

 

[Steve]

Hi peeps

i have built a outhouse at the end of my garden and need some electrical advice . i wish to install 8 sockets and 3 wall lights. The sockets will be powering 1 television, 2 x 2kw rads, 1 x 9kw water heater, 1 x 400w macerator and i would like 2 spare sockets. My consumer unit in the house has 2 spare sockets. i have bought the sockets, lights, consumer unit (6amp & 32 amp mcb's with rcd) and a lenght of 10mm twin & earth. My questions are:
a) is this do-able for someone with no electrical knowledge ?
b) does the set-up sound ok ?

You seem to be setting up a residential arrangement here. Do building control know? They will anyway, when you tell them about the electrical work.

1. Macerator - NEVER on an RCD.
2. 9KW heater - you wont be plugging this in. A 13 amp plug can supply around 3kw. You'll need another MCB for this.
2a. 2kw heaters - I'd run a seperate circuit for these, another MCB.
3. What distance from house to outhouse? You may need bigger cable due to intended load.
4. The feed from the house shouldnt be RCD protected (though you dont mention this)

If the CU you bought was a 2-way one, take it back.

 

[bluebird01]

Thanks Steve

my son will be staying with me at weekends so i need to make it habitable. the distance from house consumer unit to outhouse is approx. 100 ft. if i can swap the CU for a 4 way with 3 x 32amp & 1 x 6amp would i be more in the ball park? and how should i connect the macerator? the house CU doesn't have an RCD (phew, luckily!)

 

[plugwash]

If the cable is running underground then it needs to be armoured, size will depend on the distance as well as the loading. Given the loads you have specified the cable is going to end up pretty big even for a short run and potentially huge for a long run.

then you have to consider how you are going to connect it to the mains, a domestic CU probablly won't be sufficiant so you will proabbablly have to use a switchfuse and henly blocks.

As for connecting the equipment in the outbuilding most of it can probablly be either plugged in or on FCUs but the heater will need a seperate circuit from the outbuilding CU.

If you are converting an outbuilding to be habbitable then you will almost certainly need planning and building regs approval for it to be legal.

 

[Steve]

100ft is about 35 metres. An educated guess would tell me you need 16mm² cable for the load you describe on that distance. The next size up from that is 25mm - when I'd look at using split concentric cable, as opposed to steel wire armoured.

16mm²

16mm² prepared

25mm² terminated into a CU

^^That is what split con looks like, its actually easier to use than SWA, but not widely available for some reason. (THANKS TO LECTRICIAN FOR YOUR PICTURES, though how did you downsize them on "that other forum"?)

Alternatively, use gas for the water heating in the outhouse.

Rather than use an overall RCD (which may cause problems if it trips and someone flushes the loo), I'd have RCD provision for the sockets only. This can be done easily by using an RCBO.

^^That is my shed CU. The lights aren't RCD protected, but the sockets are. The middle device is the RCBO, its an MCB and RCD in one. The big red switch is simply a main switch, it has no protective characteristics. RCBOs are available for most boards. It has a little test button like and RCD, see?

By the way, if your house CU has no RCD provision, I'd look at replacing it. It should at least provide RCD protection for your sockets, this is guidance. The regs state "all sockets that could reasonably provide power to outdoors appliances must be protected by an RCD". This is why in your shed, only the sockets require protection.

If your main to the shed does end up requiring 25mm cable, you'll porbebly end up running it straight from the meter, like your existing fuse box, by splitting the tails and fitting henley blocks. This is a job for an electrician (more so than all the above, it requires experience)

 

[electronicsuk]

i have built a outhouse at the end of my garden and need some electrical advice . i wish to install 8 sockets and 3 wall lights. The sockets will be powering 1 television, 2 x 2kw rads, 1 x 9kw water heater, 1 x 400w macerator and i would like 2 spare sockets. My consumer unit in the house has 2 spare sockets. i have bought the sockets, lights, consumer unit (6amp & 32 amp mcb's with rcd) and a lenght of 10mm twin & earth. My questions are:
a) is this do-able for someone with no electrical knowledge ?
b) does the set-up sound ok ?

It's not in my usual style to provide the simple answer of 'No', but I think it is necessary here. You have gone and purchased parts that you do not know how to fit, and what's more, what you have purchased so far is not suitable for the job and will need to be replaced.

The CU sounds like a small garage unit with overall RCD. This does not provide enough ways, nor are the installed MCBs appropriate for the loads you describe. The 9kW heater will require a 40A supply alone.

The cable is not suitably protected, nor is it adequate for a 100ft run with the loads you describe. Please, fo your son's sake, get an electrician in to do this work.

 

[ColJack]

since he's obviously intending to have water and services to the granny flat, then he can't export the earth using the armor can he?

you'll need an earth rod and pit and a 100mA RCD because your granny flat will be TT..

your best bet might be to get a DNO to put in it's own supply with a card meter.. that way your son can pay for his own electricity..

 

[RF Lighting]

If the water supply is an MDPE pipe then it will not introduce a potential, futhermore, the bonding (and the equipotential zone) could be extended by running a 10.0mm earth in with the supply

 

[ColJack]

still, at roughly 14KW, that's about 60 amps..

if his house only has a 80 amp supply he'll have to tell his kid to turn off the heaters if he wants a shower in the main house..

better off running gas and fitting a combi for the heating / hot water...

is this flat intending to have a shower?

 

[Steve]

My post was intended to be a little intimidating / scary. Such a job as this is not normally within the scope of a DIYer, though many will be able to do it with confidence and succeed.

 

[securespark]

9kW is nigh-on 40A...

 

[plugwash]

since he's obviously intending to have water and services to the granny flat, then he can't export the earth using the armor can he?

As long as he uses a core for earth or makes sure the armours equivilent CSA is up to main bonding requirements it shouldn't be a problem to export the PME.

 

[ColJack]

as pointed out by RF..

the bonding (and the equipotential zone) could be extended by running a 10.0mm earth in with the supply

the figure of 14KW i came up with was taking the 9KW water heater, the 2 x 2KW rads, 400W macerator and extra things like lights, the tv, bound to end up with a small ber fridge and a kettle maybe..