TT systems???

[Grant M]

I recently changed a fuse box and began testing to discover the property has no earth. I put an earth rod down and my Ze is 49ohm, which is an acceptable figure according the the 17th, which requires less than 200ohm. How do my Zs readings work? I am measuring about 12ohm on the socket circuits. All circuits are RCD protected. Do I just accept these high readings compared to TN systems, is this normal? Another question I have is what size earth cable should be used?

This is only the second time I have installed an earth rod, the first being for a temp supply.

Regards,
GrantM.

 

[IQ Electrical]

I recently changed a fuse box and began testing to discover the property has no earth. I put an earth rod down and my Ze is 49ohm, which is an acceptable figure according the the 17th, which requires less than 200ohm. How do my Zs readings work? I am measuring about 12ohm on the socket circuits. All circuits are RCD protected. Do I just accept these high readings compared to TN systems, is this normal? Another question I have is what size earth cable should be used?

This is only the second time I have installed an earth rod, the first being for a temp supply.

Regards,
GrantM.

Grant, your maximum Zs readings (assuming 30mA RCD protection) will be 1667 Ohms.

Obviously in a domestic situation, you will know from R1+R2 values that your continuity of protective conductors test readings are adequate.

Will your earthing conductor be buried and if so mechanically protected?

 

[Grant M]

Grant, your maximum Zs readings (assuming 30mA RCD protection) will be 1667 Ohms.

Obviously in a domestic situation, you will know from R1+R2 values that your continuity of protective conductors test readings are adequate.

Will your earthing conductor be buried and if so mechanically protected?

Thanks for reply.
No, the earthig conductor will not be buried.

 

[telectrix]

the reason your Zs readings are less than your Ze is because the bonding to the water/gas is providing a parallel path, thus effectively reducing your Ze.as IQ said, your max value for Zs to enter on the test results is 1667 for all circuits, regardless of the MCB type and rating. your main earth cable can be 6mm , however i prefer to use 10mm if not mechanically protected.

 

[Grant M]

Thanks.

 

[Deleted member 26818]

You will require every circuit to be RCD protected.

 

[telectrix]

think he said that in his OP, Spin.

 

[p11jor]

I try to called the supplier to see possibility of getting a tnc-s system,

 

[Deleted member 26818]

think he said that in his OP, Spin.

Still learning to read, getting there.

 

[GLENNSPARK]

I try to called the supplier to see possibility of getting a tnc-s system,

Problem here is that if there is an adiquate means of earthing at the install (consumers TT) they are likely to charge the consumer to put a service head in with a neutral link (if it doesn`t have one already).............Dont forget, the DNO is only responsible for earthing their own supply cables/systems and have no obligation to a consumer other than the supply is safe to use and adiquate for the expected load (within reason).....

 

[p11jor]

Surely with the regs stating unless designated circuit (cable more than 50mm in building fabric) or have skilled person permanently onsite etc then 99.9% of the time circuits should be protected by RCD, with a sky high zs the surely nuscience tripping is a problem, these rcds are mega sensitive, so there has to be some responsibility somewhere along the line for the earthing..... Its amazing the size and man power of these distributors but soon as you mention a earth system to them they shy away from it and leave it to a man with hammer and a rod!

 

[JONOXNAM]

Going forward at least all new installs must be given an earth by the DNO:

ESQCR 24:
(4) Unless he can reasonably conclude that it is inappropriate for reasons of safety, a distributor
shall, when providing a new connection at low voltage, make available his supply neutral conductor
or, if appropriate, the protective conductor of his network for connection to the protective conductor
of the consumer’s installation.
(5) In this regulation the expression “new connection” means the first electric line, or the
replacement of an existing electric line, to one or more consumer’s installations.

 

[GLENNSPARK]

Surely with the regs stating unless designated circuit (cable more than 50mm in building fabric) or have skilled person permanently onsite etc then 99.9% of the time circuits should be protected by RCD, with a sky high zs the surely nuscience tripping is a problem, these rcds are mega sensitive, so there has to be some responsibility somewhere along the line for the earthing..... Its amazing the size and man power of these distributors but soon as you mention a earth system to them they shy away from it and leave it to a man with hammer and a rod!

Well its like this: there not LEGALLY obliged to provide an earth for a consumer but can disconnect if they find a consumer with no means of earthing whatsoever and (for whatever reason) wont comply with their demands that an adiquate earthing arrangement be provided..........

 

[Deleted member 26818]

Actually, in TN systems, it's only circuits of special locations that require RCD protection, and some believe that even those don't require the whole circuit to be protected.
The biggest problem now with TT systems, is providing discrimination between RCDs in series, what with the reduction of disconnection times in the 17th edition.

 

[GLENNSPARK]

Actually, in TN systems, it's only circuits of special locations that require RCD protection, and some believe that even those don't require the whole circuit to be protected.
The biggest problem now with TT systems, is providing discrimination between RCDs in series, what with the reduction of disconnection times in the 17th edition.

So that rule out a 100mA s type then spin?