supply to log cabin

[webby_58]

hello all

i have to get a supply to a log cabin and have the following arrangment :

TN-S supply in house
House CU MCB's no RCD
supply to garage CU via 16amp MCB (2.5 t/e) / garage CU has 63a 30ma RCD
approx 35mtr to garage and 50mtr to house in cabin approx 6 sockets maybe an electric heater and 1 light circuit

i propose to spilt the tails in the house into 100a henley block and take a new swa to the cabin. CU in cabin with 30ma RCD 6a MCB for lights 16a MCB for socket ring

my query is the cable size. do i have to use 10mm swa 3 core to provide the correct size earth ?

what would be the best way to do this also taking into account cost.

please help.......!!!!

thanks in advance guys.

 

[IQ Electrical]

Normallly I lay in wait until someone comes on here and says something intelligent to say and plagerize ......................getting harder and harder to do, or the wait is getting longer ...............

Are you on the right thread?

 

[Hawk81]

OK could not find the reg!!!

The problem is the potential (arrgh) of touching two different grounds.

In the event of a L-E fault current will flow down the ground rod and the ground voltage will rise due to the ground resistance, often this voltage can get rather high before the protective device opens. If you happen to be in contact with the 'live' ground and a 'real' ground at the same time things can get bad

This is the reason for equipotential bonding, to ensure all grounded metalwork is at the same potential (they're connected together).

So long as all earth stakes that serve a particular building are connected to a single main earth terminal (MET) there is no danger, it's common to use multiple earth pits in commercial buildings in order to get the ground resistance down to acceptable levels, they're all linked to a single MET.

In your outbuilding it's actually safer to have a local ground, if you do export the house ground and there's a fault any metalwork connected to the ground terminal will rise towards L potential, if there's a water pipe in the outbuilding it will remain at 'real' ground, ouch if you touch both. This is the reason that exporting PME earth is prohibited in certain circumstances.

IMO I will install an rod, with rcd

I think you did not find the reg as it does not exist like I told you. What are you talking about PME for when the op said TNS. Quite simply you were wrong. End of story.

 

[Guest 004]

I think you did not find the reg as it does not exist like I told you. What are you talking about PME for when the op said TNS. Quite simply you were wrong. End of story.

Just back from the pub are we?

Yes indeed it applies to TNCS systems, but as the OP states it was TNS, so does not apply.

 

[Hawk81]

Just back from the pub are we?

Yes indeed it applies to TNCS systems, but as the OP states it was TNS, so does not apply.

I was not at the pub. What does that mean? Have you just admitted you were wrong then?

 

[Guest 004]

As it was TNS yes indeed I admit that there is no reg for it.

 

[Chr!s]

422.4 has requirements but they are more concerned with luminaires and wiring systems within the combustible structure.

Well in the opening post he mentioned wiring within the cabin, so needs to meet 422.4 CA2

 

[Guest 004]

IME I have not come across many TNS supplies, and indeed even less TT supplies, and given the reference supplied by IQ, I would still not export an TNS earth, but rather go with the option of a TT system creating its own EZ.

 

[Engineer54]

IME I have not come across many TNS supplies, and indeed even less TT supplies, and given the reference supplied by IQ, I would still not export an TNS earth, but rather go with the option of a TT system creating its own EZ.

Why's that then?? Why on earth (excuse the pun) would you ditch a perfectly good earthing system for an unstable one???

 

[Guest 004]

Have you read the whole thread?
and why would it be unstable? that is only if the earth rods was over 200 ohms? highly unlikely

 

[webby_58]

hi there

i am planning to connect the new swa from henley block into a fuse switch to isolate supply.

regards

 

[Guest 004]

hi there

i am planning to connect the new swa from henley block into a fuse switch to isolate supply.

regards

good luck with that

 

[Engineer54]

So you would honestly ditch a TN-S for a TT system ?? ...words just escape me!!!

 

[Guest 004]

So you would honestly ditch a TN-S for a TT system ?? ...words just escape me!!!

well take a deep breath, and try to get some words out, I will listen very carefully, and take in any positive input you have.

 

[Engineer54]

I would much rather You explain why you concider 200 ohms Ra is preferable to 0.8 ohms Zs, as your proposed earthing system??? I look forward to your explanation...

 

[Guest 004]

because the fault current required to open the circuits is much lower