Which is the cable to the shed?  Can you mark the Live and Neutral in the consumer unit to show us which ones (use Paint in windows).

Sounds like you have muddled up the neutrals.

If you are feeding the garage from the 30mA RCD side of the main consumer unit you do not need any RCD in the consumer unit in the workshop.

Ideally (depending on installation method of cable), you would have the cable to the workshop ont he NON RCD side of the main CU, and then a 30mA RCD in the workshop CU.

How does the cable run to the workshop?
What type and size of cable?
What have final circuits do you have in the workshop?
What type of loading (equipment) have you got?

Photos are always useful.

This is a photo with the workshop fuse in place, the cable is 6mm twin and earth, im  a bit short of time at this moment im off to church in 20 mins but when i return ill post a photo of the fusebox in the workshop and answer the rest of the questions.  The cable is underground in trunking

got back too late to take any photos, but will tomorow, thanks for some interesting information. Ill change the fuse for the correct type, b32 i think, regarding the cable underground i was told by a electrician this would be fine as long as it was in a sealed trunking, this i did, he works for a housing association, thats worried me a bit now you tell me its not safe as it cost a lot of time and money to get this done. ok ill put more photos up tomorow, regarding the 4th fuse from left, thats a brown wire serving the cooker.  and the green is paint on a 2.5 mm and that is feeding a double socket

I'm now running on the left side of the C/u into a b20 amp mcb, it runs the immersion heater but we always use gas, so till i go out and buy a b32 amp mcb it will do for testing, i also moved the neutral to the left, then checked in the workshop and it now works fine, the photo shows the C/u in the workshop, Ive only fitted one socket to start but will be fitting lighting and other sockets to the C/u later this week.

The first photo is with the cover removed (workshop), the second is with cover fitted (workshop), i think i need to buy two blanks to stop fingers getting in, who sells the covers for this type of box?. would it be advisable to fit a separate earth rod to my workshop C/u too? Doug.

This Any good? and yes a good idea would leave room for 2 more mcb/s
http://www.tlc-direct.co.uk/Products/MK5590.html?utm_source=shopping.com

OK ill buy that B20 the same time i get one for the house Cu.  the neutral and live come from under the isolator to the top of the RCD then the neutral comes out the bottom of the RCD and onto the neutral rail, the live goes on the the base of all the mcb/s that i need a bus bar for.

I checked the wiring twice behind the socket and it was correct, i thought it may have had something to do with the distance from the RCD to the workshop Cu, the RCD in the house is very sensitive, it trips even when a bulb blows in the house. there are earth wires all over the house clamped to every possible point upstairs and down.

the silver on the 6mm cable is tape that was used to keep the coil of wire from getting in knots.

when i had the system running on the RCD in the house it tripped every time "anything" was plugged into the socket in the workshop the RCD in the workshop never tripped, if i plugged the same appliance into a socket in the house it was fine.

I want to thank all of you for giving me your time and skills, your just what i need, this is a fantastic site, I'm  going to enroll into my local college for the City and Guilds 2392 Part P, Domestic installers certificate, I've passed my part 1 some years ago but had to leave through ill health.

make sure the supply cable to the workshop isnt damaged at any point ,especially where it enters the fuse boards

also,have you put a socket tester into the twin socket in the workshop ?

if not try that if you have a socket tester,or if you dont have a tester,try changing the twin socket for a different one,then try plugging your items in again
there is a chance it "may" be that


it would probibly only be the rcd in the house that would trip rather than the rcd in the workshop if there is a fault,as it will go back to the origin of the supply first,hence tripping the house rcd