TT systems

[sparky40]

Thank you all for your help on that one.
Looks like I win the tenner !

Slippyr4 had it right from the start then !!!

Thanks again.

 

[Big_Spark]

Thank you all for your help on that one.
Looks like I win the tenner !

Slippyr4 had it right from the start then !!!

Thanks again.

2.5mm² conductor will not comply with the Regs though, so therefore he was not correct. Without knowing the actual resistance of the Earth Rod, as measured in the prescribed fashion, it is foolhardy to state that a given size cable will be sufficient without a proper calculation and adherance to BS7671.

 

[securespark]

If it is protected, table 10C states 2.5mm2.

Why?

 

[Big_Spark]

If it is protected, table 10C states 2.5mm2.

Why?

Simon, all I can refer you too is section 542 of Chapter 54 which deals with the Earthing arrangements of different supply types.

542-01-04 states

For a TT or IT system, the main earthing terminal shall be connected via an earthing conductor to an earth electrode complying with Regulation 542-02

Now 542-02 states quite a bit I will not type here, but basically it states in 542-03 that all such conductors must comply with table 54A for BURIED cables, or 54H for for the MEBc's.

I do not see how it is possible to install a rod correctly without at least part of the cable being classed as buried as the head of the rod should be below grounbd level in a pit...or perhaps I am being pedantic on this point?

 

[Darkness]

Are sparks using earth pits these days cause the last few house I've seen built including the house next door to me which has just been built, the connection part of the rod is cover with a galvanised earth electrode Box which is cemented flush into the patio/path around the house.

The 16mm2 cable is then buried underground straight to the CU.

To look at it, you'd think you have got a floor socket on your path but when you lift the lid, yout see the earth rod. I'm seeing this method alot now.

 

[Big_Spark]

They stillcall it an Earth Pit as it is below ground level..generally it is only lightning protection companies that utilise premanufactured pits, but that isnot a hard and fast rule..

 

[Darkness]

Ah right.

If running water from the path was getting into the box after a good down-pour, would this not cause problems or would it help in the earthing keeping the ground around the rod wet?

I thought damp was better than wet wet.

 

[securespark]

I do not see how it is possible to install a rod correctly without at least part of the cable being classed as buried as the head of the rod should be below ground level in a pit...or perhaps I am being pedantic on this point?

Well, some rods i've seen have the conduit box screwed to the concrete surface, so are not below ground.

But even if they were, the 2.5 is for either buried or not buried, is that not right?

 

[sparky40]

Hello All,
As I am quoting from pg 163, table 10c, the conductor size for an 'earthing' conductor is 2.5mm if it is protected against corrosion and mechanical damage.
I understand and respect your statements Big Spark, I am not doubting your knowledge but it says it here in black and white, so even though it 'seems' very small to me, it is the correct size ?.

Thanks All,

 

[sparky40]

Hello All,
As I am quoting from pg 163, table 10c, the conductor size for an 'earthing' conductor is 2.5mm if it is protected against corrosion and mechanical damage.
I understand and respect your statements Big Spark, I am not doubting your knowledge but it says it here in black and white, so even though it 'seems' very small to me, it is the correct size ?.

Thanks All,

 

[sparky40]

Doh. !

 

[Big_Spark]

I assume your looking in the OSG, which I do not have to hand.

From memory and the main book, the only earthing conductors that can be 2.5mm² protected and 4mm² if unprotected are SUPPLEMENTARY BONDING CONDUCTORS, and a connection to an earth rod is not one of these.

If there is somewhere in the full BS7671 for this, please give me the reference as I am unable to find it in my book, on the IEE website or the NICEIC site.

EDIT

Found my OSG..in a box of CD's!! (don't ask)

Found the table you have all referred to and see what your going on about and would direct your attention to Note 3 at the bottom, further, I still maintain that the conductor from the rod to the MET should still not be less than 50% of the csa of the Incoming conductors. The figure on the table flies in the face of several other Regs in BS7671..

 

[securespark]

We need to question why it recommends these figures, then.

 

[sparky40]

Sorry Lad's

I don't know where I should be looking to give me the knowledge to confidently answer my question, please do help if you can as it is probrobly something that I should already know, ( and don't , but do want to ! )

Sorry to draw the question out .

Thanks.

 

[Big_Spark]

We need to question why it recommends these figures, then.

I agree Simon as it flies in the face of Reg 542-03-01 and table 54A.

Sparky40, don't worry about dragging it out..good topis for discussion as it is clear there may be conflicting information in the main BS7671 and the OSG..which would be no surprise to me..