Bonding query in outbuilding

[sammi100]

Hello
I am currently doing an electrical course at college and have a query reguarding TT circuits.

This is the scenario :
For my theory project i have to imagine i'm wiring a detached building.
It will consist of a new Consumer unit ( 1x 6amp breaker and 1x 16amp breaker) which will feed 4 x 2gang sockets in a radial circuit and one Two way light set up (1x Strip light).
The consumer unit it connected to the main house Consumer unit on it's RCD side by 4mm SWA (3 core).

Where i'm stuck is, as the SWA has an earth attached from the main Consumer unit to the New detached building unit, do i connect the Earth OR do i need to install a Earth Rod (16mm or 10mm Bonding) instead ?

In other words, do i :
A) leave just the Earth from the 3 core SWA attached ?
B) Disconnect the SWA's earth and fit a bonding to an Earth rod ?
C) Attach the both of these (i beleive this is wrong due to conflict to the RCD?) ?

I hope i've explained my question enough.
Thank you.

 

[oharaf]

The 3 Core SWA is connected to earth at the CU in the house and so will need connecting to the earth bar at the 'new' site.

Not forgetting to connect the armour to earth at both ends!!

You will then need to test to see if the impedance is sufficiently low to carry away fault current.

Now 4mm is quite small, however, as you say it is protected by an RCD at the house, so, when you have carried out your continuity test, IR test, EFLI test and then your RCD test from the Incomer at the new 'site' you will be able to review your readings.

A few Questions

What do you think is an acceptable values for

Continuity of your earth?
IR between conductors?
EFLI for your Supply Circuit? (the SWA)
RCD tripping times?

Also

Would YOU be happy with relying solely on one of the cores providing the only means of earth to the new 'site'


Sorry to throw questions back at you, but you need to think things through yourself as well as ask.

What problem do you foresee by providing an Earth Rod at the supply as well as the exported earth??

Mine field I know!!!