TT System with TNS reading

[LastManOnline]

However, you cannot depend on that! You have absolutely no control over its presence and any replacement pipes could be plastic, etc, and render it useless.

When replacement of metallic services with plastic really started to take off , it compelled the DNO,s to review their supply system type.At the time I hoped to cash in on this change by alerting homeowners in advance to the potential consequences for their installations and advise on what changes ,if any, they would need to make.
Firts I needed to contact with the DNO,s and the providers of services (water and gas etc) to establish what their plan of action was .The result ?.There appeared to be no plan and little or no co-ordination between the various services.It was all very haphazard.Services were replaced. homeowners would start to get "tittles" from the sink (or worse) and the electrician is then called in.
I could,nt establish which services would be making replacements in which locations.
Aside from a business opportunity gone out the window,a great opportunity for a reliable earthing system was lost.
Much of the replaced metalwork was actually left in the ground and could have been reused, providing a perfect earth rod for a TT system and a great protection against an open PEN in a TN-CS system.

 

[pc1966]

Took an earth loop reading at the board and tester shows 0.41ohms with water bonding disconnected.

I would just add that disconnecting the service pipe bonds does not guarantee the installation's CPC is isolated. Very likely you well find they are still linked via an immersion heater CPC, boiler CPC, gas hob ignition CPC, etc.

 

[Rockingit]

If you think about it.....your installation might be TT, but the building down the road may well be TNCS. If an incoming 'common' water pipe servicing the road is metal (cast iron!) then that same pipe is also being EQPZ bonded internally down the road - straight on to the DNO's earth. Hence how you can get really low readings.

 

[LastManOnline]

If you think about it.....your installation might be TT, but the building down the road may well be TNCS. If an incoming 'common' water pipe servicing the road is metal (cast iron!) then that same pipe is also being EQPZ bonded internally down the road - straight on to the DNO's earth. Hence how you can get really low readings.

Key point that.It means you could walk away from your TT installation and not appreciate that you are vulnerable to your TNCS neighbours issues.
An open PEN could result in the neighbouring houses current trying to get back to the DNO,s trafo via any available cpc in your house.