Earthing Arrangements Supplying A Garage 16M From House Tn-C-S

[theitman]

Just need a conformation of regs here for my competent person scheme assessment.

The job I am doing is running SWA cable at a depth of 600mm from the house off of CCU.

The house is TN-C-S (PME), am I correct in saying that I can not extend the earthing outside the house and instead would need to use earth electrodes (TT) to supply the garage.

Cheers

Paul

 

[steptoe]

the simple answer is,

there is no simple answer,

there is a lot more to it than simply extending the earth,

is it simply TNCS or proper PME?

 

[betty swollocks]

Choose a nice easy job for your assessment, the easier it is the less you will stress about covering all the angles and crossing all the rods.

As stated there is not a simple defined answer so whichever method you use, is no guarantee your assessor will agree

 

[pewter]

i would whack a rod in 

dunno what your all scared of its only a garage

 

[steptoe]

i would whack a rod in 

dunno what your all scared of its only a garage

but you may not have to.!

 

[SLIPSHOD & SLAPDASH]

but you may not have to.!

Probably cheaper !

 

[steptoe]

Probably cheaper !

than NOT having to buy a rod?  :C

 

[SLIPSHOD & SLAPDASH]

Than additonal cores or bonding, as we dont know the exact details

 

[Dug]

Surely if you have a low enough loop impedance at the garage you will be ok?

 

[SPECIAL LOCATION]

Are there any extraneous metal parts in the garage?

 

[steptoe]

Surely if you have a low enough loop impedance at the garage you will be ok?

you COULD have a potential difference of your 'exported' earth and the actual mass of earth earth.

you should see the overkill I have for my shed, and its wooden with no extraneous parts, 

but what do i know about earthing,?  :slap

 

[theitman]

Are there any extraneous metal parts in the garage?

No

the simple answer is,

there is no simple answer,

there is a lot more to it than simply extending the earth,

is it simply TNCS or proper PME?

Proper PME

 

[steptoe]

then localise it at the garage would be my preferred solution.

Proper PME

 

[theitman]

It is a proper PME system, 6mm  3 core SWA cable off a 32amp MCB at the house consumer unit supplying lights and sockets in garage.

I had originally exported earth using third core, but on consulting regs found that I need earth rods.

No

Proper PME

Yes

 

[steptoe]

It is a proper PME system, 6mm  3 core SWA cable off a 32amp MCB at the house consumer unit supplying lights and sockets in garage.

I had originally exported earth using third core, but on consulting regs found that I need earth rods.

Yes

if you want to continue as PME its not always just a simple case of banging a rod in though.

 

[theitman]

then localise it at the garage would be my preferred solution.

Cheers for this, thought it was the way to go, just wanted conformation from an experienced electrician.

 

[steptoe]

you have to be careful of how you do this though, a lot can depend on the type of soil etc you have between your incomer, your shed/garage, and the first point of rodding on the DNOs side,

I wouldnt simply just be rodding it at the garage and hoping that is enough for the PME to stay intact/good,

although you could do that and then take some measurements to confirm or otherwise what else is required, if anything.

 

[pewter]

the simple answer is,

there is no simple answer,

there is a lot more to it than simply extending the earth,

is it simply TNCS or proper PME?

How can you tell?

I always thought it was the same. (TNCS, PME)

I know an ex DNO guy that tells me its the same.

On the western power web site linked on the other topic about the split phase it has 'PME, known as TN-C-S within BS7671'

Only on here have i heard of TNCS and 'proper PME'  been different things

I am not trying to pick a fight, just interested as i have always been taught its the same and everyone i know in the trade thinks it is the same also.

 

[steptoe]

by the end of this year, unless they have changed the dates, it should be the same,

but, in reality it isnt,

I done a post a while back on basic earthing arrangements,

Im fairly sure its pinned in the student section,

its a very often mistake to make as to TNCS and PME being the same, and in all honesty, when you look at the simple version of it you will then wonder iof the DNO really is upgrading it all, or simply doing a sticker exercise.

 

[pewter]

So how can you tell which type it is?