TNCS system with supplementary TT rod

[platty1005]

Hi IQ if there are 2 cables line and neutral to the property from the main 3P&N pole system and this neutral cable breaks HOW can that property become the PEN for the whole street. If the main neutral breaks the system is tied to earth approx every 100yards as a PME system. Installing a Rod at the property is just the same principle as the DNO installing electrodes along the PEN safety if the neutral breaks

 

[IQ Electrical]

Hi IQ if there are 2 cables line and neutral to the property from the main 3P&N pole system and this neutral cable breaks HOW can that property become the PEN for the whole street. If the main neutral breaks the system is tied to earth approx every 100yards as a PME system. Installing a Rod at the property is just the same principle as the DNO installing electrodes along the PEN safety if the neutral breaks

Yes I was going OTT with the 'whole street' scenario but you can still cram a few installations into a '100 yard' terrace.

 

[platty1005]

Touche I follow your thoughts on terraced houses
But if this system is used careful consideration of the size of earthing conductor to the TT rod must be given with regard to the size of Line/Neutral feeding the terrace IE same size as the main Live conductors. IE as per regs for a Pen system not as per regs for a TT

 

[Knobhead]

I hope not, you end up becoming the PEN for the whole street in the (very rare) event that an overhead neutral breaks.

It always sounds good in theory when people talk of 'tying down' the MET but in reality the probable Ra of the electrode is prohibitive and other damgers can actually be introduced.

It can and does happen, my house being the one providing the PEN connection for 12 houses. See http://www.electriciansforums.net/electrical-forum-general-electrical-forum/21227-tingley-taps.html

 

[Engineer54]

If the supply is a DNO PME system, there is no problem connecting an earth electrode to the MET. Quite a few of our European cousins insist that a local rod is installed at each installation especially on domestic installations. But notice i said connected to the MET, and not at the DNO cut-out!!! lol!!

 

[SW1970]

Thanks folks. Really valuable contributions as usual. This is one of those jobs I just can't wait to get to! Be really interesting to see how this earthing is actually set up.

 

[Knobhead]

Not as a criticism to or of anyone. But I wonder if this argument will ever end.

The UK distribution system is in a MESS! All down to (in my opinion) to lack of investment in maintaining the infrastructure, but prices would spiral to correct things now. So unfortunately we’re stuck with an imperfect system.

PME would be the perfect system, IF IT COULD BE GURANTEED.

I personally would have an earth rod at every PME termination. But that would require zero distribution cable faults (I’m in cloud cuckoo land again).

We can argue until we are blue in the face, we’ve got a sh*t set up!

 

[netblindpaul]

All good posts, OP, is there or was there a swimming pool at the premises?
This has been mentioned once earlier in the thread and not followed up.
If so then there should be a rod at the DB supplying the pool install, check the regs.
This could be the situation?

BTW yes the Local DNO networks are a MESS!
We are also fast approaching the cut off for the DNO's to PME their TN-C-S networks. IIRC they have just under 12 months to complete this.
A true PME network would have a rod at every DB in an install anyway, as well as every tap off and joint in the DNO net.

 

[SW1970]

Hiya, no pool current or past. When I get back there I'll get some decent photos of supply and earthing arrangements. I'll be doing a design drawing to address the fairly high demand at the property; this could form a good case study for 2391ers. I'm willing the customer using jedi powers to phone me up and order the PIR.