would this be STOOPID- an electrical question.

[Fil]

before i blow myself up...

is earth always earth, or are all earths the same?

if i have 2 x spurs off 2 different ring mains would connecting the earths together be a problem?


my brewshed is fed by 2 x 2.5mm sq extention leads.
between the power sources and the brewshed is a wooden shed with a now tight roof

ive been given a 5 core 2.5mm sq armoured cable that could become a permenant bridge between the wooden shed and the brewshed.

i could shorten my extention leads if i ran them to the back end of the wooden shed rather than to the brewshed. running the feeds thru conduit in the shed eves

but to run 2 x 3 core feeds over a 5 core wire??? would sharing the earth compromise actual safety?

could i employ the steel shield as a 2nd earth?

only problem i can see is if i connect the earths up and then split again or create a common earth within the brewshed a single short will blow both mcb's in the consumer unit, unless i use 2ndary rcds in the brewshed.

[GrowlingDogBeer]

My advice.

Find a local qualified electrician, tell them what power you need in the brew shed and let them sort it out.
It will be much safer.

[Jim]

I take it you're aware of Part P of the building regs? Certain electrical work must be carried out by a suitably qualified electrician. Permanent supplies to sheds and outhouses fall into this category.

Getting the earthing right for this type of installation is tricky and critical, so I wouldn't advise you to wing it if you aren't sure what you're doing.

(EDIT: Cross-posted with GDB)

[boingy]

I know you're not going to get a sparky to do it so the next best advice is to forget the free 5 core stuff and run two lengths of the proper 3 core armoured stuff. 25 metres of 2.5mm sq is £35 from Toolstation:

http://www.toolstation.com/shop/Electri ... 730/p57367

(Does it need to be armoured? Will you be burying it?)

Definitely don't do anything kooky with sharing/combining/splitting earths. Just don't.

[Jonnyconga]

I agree with the other comments. If you are winging it, wing it as safely as you can. Look on lots of DIY websites and don't do it if you aren't sure. (Got any friends who are electricians?!)

Re the armoured cable - I'd say it's even more important to be armoured if you aren't burying it - a stray spade, hedge cutter etc can chop through a bit of flex easy - not the case for armoured cable.

[Fil]

cheers for the input..

longterm a nice big workshed will stand in between with a real full power electricity supply daisy chaining all the way up there installed by pro's fully upto spec with enough amps to maintain a 3 bedroom house. the foundations are 1/2 sorted, meanwhile i will be continuing to brew with the temporary supplys plugged in on brewday, the cables lie where they are unlikely to get spaded/trimmered as im the only one who does that sort of thing and never on a brewday..

Without the interim workshop, its cheaper to install a 2nd meter point branching off a neighbours supply than a trace from our meter point/consumer unit a real supply.
short term im hoping to cut down on the length of 2.5mm sq flex i have to coil up n store at the end of the day... as it is the 2 cables fill the outside bog wall to the point of nuisance.

Part P hrmph!! well what im proposing is just the tail end of a temporary feed hrmph!

[themadhippy]

Before you get to chose the cable you need to identify the type of earthing arangment on the incoming supply, if its tnc-s and your brew shed is outside the equipotential bonding zone you'll need to provide alternative earthing arangments.youll also have to determine the r1+r2 values to make sure the disconection time complies,o yea and dont forget the grouping factor for 2 circuits combined in 1 cable when doing your cable size calculations

only problem i can see is if i connect the earths up and then split again or create a common earth within the brewshed a single short will blow both mcb's in the consumer unit, unless i use 2ndary rcds in the brewshed.

Erm no ,as the overcurrent will only be on 1 protective device.

[e--brewer]

My tup-pence worth would be
Sounds like you really aren't certain what your doing and if your not ,don't take a chance hire a spark who will ,design the system ,install it , test it and then issue you with a works certificate to certify its safe .
I am Not a sparky but have a fair bit of interaction with the industry and it sounds like you have multiple issues to contend with .
From what you describe I am guessing that the Brew Shed is a fair distance from the Main Hoose .
So you will have issues with voltage drop etc So cable selection will need a bit of working out accordingly.
Likelyhood is that the BrewShed would be fitted with a small consumer unit which will be earthed by an Earth spike which spike will have to be checked to make sure its good enough
That the existing Power to the nearby shed isn't adequate anyway far-less daisy chaining of that supply.
The amour could be used as the earth but getting a good connection to the gland isn't that easy for a diyer.
Do you have access to a 'megger' as it will be essential to test any installation properly .

[Fil]

TMH Glad to get your input, even tho its a polite way of saying "there is way much more to it and your out of your depth"

oh well i will just have to step over extention leads coiled up in the outside bog for a lil longer then.

e--brewer, the voltage drop is 4 to 6v i measure 244 at the house, and 240/238 at the brewshed. not ideal but livable with. the advise i have gotten from a friendly sparky who has seen the layout and installed the garage feed is to finish the workshop and upgrade the suspended armoured cable to the garage, The 10 x 4m workshop will stand 2m behind the garage and will stand 4m from the wood shed which is 2m from the
brewshed building.. digging 1 x 4m trenchand suspending armoured cable between the close buildings is a lot easier than digging one huge m-fkr thru the patio, lawn, paths n vegie plots.. what uproot me hops ???? oh and not forgeting negotiating the 4 ft up 3m across and 2foot down concrete plinth the woodshed sits on (houses built on a slope).

[Old Hooky]

I just want to point out that just because a Sparky has the necessary documentation and qualifications, doesn't mean you will get it done right if he sends a monkey to do the job. We had an extension built a few years back and the guy who was going to sign off the work had two idiots wiring everything up. I had to get him down here to question why the lights didn't work properly. Anyway we got it sorted and as far as I know there was no danger, but it does make one question the usefulness of all these certificates that are imposed on us now.

[e--brewer]

I am not a fan of the Part P silliness doon in England the whole way it works seems very strange to me with people with very little background allowed by the part P schemes to work on peoples homes with as little as five weeks training.

I still reckon you need a spark to make sure you get the earth side of things sorted.
Probably a TT system a big earthspike in the garden next to the shed with the consumer unit.

why not post on one of the sparky forums offering a gid session on yer beer in exchange for doing the work but caution always due to the part pee five weekers

[Jim]

I hate part P with a passion.

I was an electrical engineer and worked for about 15 years in a high voltage/high current testing lab - I also have and OND in electrical engineering and a degree. Despite that, I am not allowed to wire my own f***ing shed up!

[Beershed Brewer]

Ok for what it's worth the best and safest option is get a qualified sparky in and ask his advice. Do the mindless donkey work yourself, ie digging trenches and running cable then get he sparky to test the circuit before connecting the ends. It's the way i did it. Still cost money but it was safe. And he was a mate!

Jim; I'm sure the regs say, but don't quote me on this, "by a competent person", surely with your qualifications you are quite competant?

[irv]

Jim; I'm sure the regs say, but don't quote me on this, "by a competent person", surely with your qualifications you are quite competant?

That is how i have interpreted it too, but i have never actually properly read over the Part P documentation.

[Jim]

The problem is you need someone to test and certify it. The cost of doing that yourself is prohibitive, and unless you have a mate that will do that bit at a reasonable cost it's nearly as cheap to get them to do the whole thing. Most leccies won't be happy about certifying someone else's work anyway apparently.