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.

 

[Deleted member 9648]

Cant believe this has come up again......no matter how many times we go over it there is always one who will pop out of the woodwork and insist an outbuilding must be separated.
But as Hawk points out,they never seem to be able to quote the regulations applicable.

 

[Chr!s]

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

Cheers IQ

Not got any reference to hand, that may be the one.

 

[Guest123]

just to throw a spanner in the works here.

If the summerhouse contained a hottub with extraneous parts ect, would there be a danger that there would be a potential difference between the ground that awet person may step on, and the earth from the TNS system that you have in the installation?
This in theory could cause a shock to somebody whp's resistance would be very low due to being wet.

In this circumstance, can you supplement the TNS earth with a rod, in order to bring the TNS earth to the same potential as the ground around your installation?

Ill be very interested to hear your replies

John

Absolutely.

In most cases of hot tub installs, the hot tub manufacturer will insist you install an additional earth rod adjacent to the hot tub in addition to an exported earth (if any) for this very reason.

 

[High Tower]

Thanks Len

 

[Guest 004]

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

 

[IQ Electrical]

If the requirements for main protective bonding are carried out within the outbuilding, how can 'any metalwork connected to the ground terminal' become live?

The OP is discussing a TN-S earthing system with far less stringent requirements for protective bonding conductor sizing so even the economic argument doesn't work on this scenario.

Guidance Note 8 has all you need to know on exporting earths, Figure 5.15 has particular relevance to this thread.

 

[mogga]

HASNT anyone else seen this line?

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

no mention of protection just split tails into henley blocks??

 

[Guest123]

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 statement confuses me slightly as surely if there were any extraneous conductive parts within the summerhouse then these would be bonded to the EMT also????

 

[IQ Electrical]

This statement confuses me slightly as surely if there were any extraneous conductive parts within the summerhouse then these would be bonded to the EMT also????

Exactly what I was trying to point out in post 36 that's the whole principal of an equipotential zone.

 

[Guest123]

Exactly what I was trying to point out in post 36 that's the whole principal of an equipotential zone.

Sorry mate, I was studying MrEnigma's post for a while to make sure incase I misunderstood it, so I didn't see yours.

The GP has started now too!!

 

[IQ Electrical]

Sorry mate, I was studying MrEnigma's post for a while to make sure incase I misunderstood it, so I didn't see yours.

The GP has started now too!!

Lol, I've got Premier League withdrawl this weekend so the GP is no use to me!

 

[malcolmsanford]

HASNT anyone else seen this line?

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

no mention of protection just split tails into henley blocks??

You will need to fit a swich fuse or similar to protect the SWA after the henly blocks.

From post 2 mate

 

[mogga]

teach me to practice wot I preach malcom READ before posting lol cheers

 

[IQ Electrical]

teach me to practice wot I preach malcom READ before posting lol cheers

I missed that too, I think Malcolm found a way of inserting posts!

 

[malcolmsanford]

I missed that too, I think Malcolm found a way of inserting posts!

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 ...............