TNS system in house built in 1929 in Croydon

[timmy123]

Looking to change consumer unit in this house and following ZE tests and examination of the incoming supply I cannot identify any incominmg earth. Also no sign that an earthing point has been soldered/weeped onto lead sheathing.Supply cables appear to be in lead sheath then enclosed in steel conduit .ZE reading is 30 Ohms. No equpotential bonding present on gas and water supplies.
As the house is in suburban croydon I am assuming that this is not a TT system.

I would appreciate any comments on this scenario and advice on getting a decent earth connection installed. Is this the electricity suppliers responsibility?

Many thanks for your comments

 

[bugsy]

Code 2

 

[timmy123]

Code 2

many thanks for your info

 

[Des 56]

I believe they are responsible for maintaining and correcting an existing earth system that they provided
If there is no earth,they are not commited to suplying one, they may very well charge you to provide one
They could also tell you to supply your own TT

With a lot of luck,they will upgrade the system at no charge


No, changed my mind,they will charge you whatever they can get away with

 

[RJS Contracts]

Every time I have had a high ZE reading I've phoned the board and they have sent someone out immediately free of charge and fixed it!! Believe it is there responsibility unless TT system!

 

[pevvers]

Code 2

Really? Code 2? The house has no decent connection to earth, which is the way that the whole ADS system works... If there was an RCD main swich at 300/100mA then yes I would agree, but if it's an old installation and all you have is MCBs or fuses protecting the circuit, then with a 30 Ohm earth fault path the protective devices ain't ever gonna trip, as in a worst case earth fault scenario the fault current won't even reach 8 amps!!

Code 1, electrical danger notification issued due to there being no adequate means of earthing for the installation... Call the board ASAP.

No main bonding I agree with as a code 2.

 

[chris gray]

its not a tn-s system then? its an old installation so probably didnt supply an earth back when initially constructed. the pipework would of been lead which would of been used as the main earth. our local electricity supplier took 6 weeks to convert to a pen and didnt charge anything.

 

[pevvers]

Surely if there was no earth at all, somebody in 81 years would have noticed it? Is the distribution board also from the 20's?

I can't say that I know much about supply regulations from that far back in time, but I do know that TN-S supplies that use the sheath as an earth have a habit of degrading over time. Is there any chance of checking the premises either side of the one you're working on to see whether they have an adequate earth?

 

[chris gray]

Surely if there was no earth at all, somebody in 81 years would have noticed it? Is the distribution board also from the 20's?


yeah you would of thought so, the number of properties we go to and there is no provision for earth and you find the main earth shoved behind the yeb board is unreal.

 

[pevvers]

yeah you would of thought so, the number of properties we go to and there is no provision for earth and you find the main earth shoved behind the yeb board is unreal.

The joys of working from a different set of rules eh?!

 

[timmy123]

Thanks for your advice and will get the supplier in asap

Many thanks for your comments. Have now arranged for supplier to visit location. All points noted and appreciated.

Really? Code 2? The house has no decent connection to earth, which is the way that the whole ADS system works... If there was an RCD main swich at 300/100mA then yes I would agree, but if it's an old installation and all you have is MCBs or fuses protecting the circuit, then with a 30 Ohm earth fault path the protective devices ain't ever gonna trip, as in a worst case earth fault scenario the fault current won't even reach 8 amps!!

Code 1, electrical danger notification issued due to there being no adequate means of earthing for the installation... Call the board ASAP.

No main bonding I agree with as a code 2.

Just re read your helpful reply ..could you point me in the right direction on what an ADS system is?? Many thanks
timmy 123

 

[pevvers]

Thanks for your advice and will get the supplier in asap

Many thanks for your comments. Have now arranged for supplier to visit location. All points noted and appreciated.




Just re read your helpful reply ..could you point me in the right direction on what an ADS system is?? Many thanks
timmy 123

Yup, sure can. It's automatic disconnection of supply. It's used to be EEBADS under the 16th, i.e. earthed equipotential bonding and automatic disconnection of supply, but the the EEB bit was dropped in the 17th. It's the safety system we use normally for making sure that in the event of a fault the system disconnects the fault. For example, fault to earth on a normal TN system will cause and MCB to trip or fuse to blow without anybody switching anything, hence the ADS. But you have to have an impedance low enough for enough fault current to trip the device, so you need an adequate earth. For TT systems, ADS is achieved by the use of RCDs, as the fault current to earth will not be high enough to trip an MCB, but only 30-300mA fault current is needed to trip an RCD, instead of a minimum of around 30A to get an instantaneous trip of the lowest and quickest MCB you'll find normally which is a B type 6A. There are other methods of protection available, but these are specialist areas, such as having non conducting locations (IT supply), but I've yet to come across one so haven't had to look into them too much. I hope this helps, and it's a pain to write this on my mobile!!