Benefits of a TT system?

Crosswire · Jun 15, 2014

If an installation is supplied by a two wire system (E.G. a TT system) , what are the benefits of using an earth electrode instead of simply joining earth to neutral at the supply head to create a TNCS system?

Surely using the supplier's neutral is a more effective return path for fault current than relying on the earth electrode and the solid mass of earth?

All replies welcome,

Cheers,
Crosswire.

Knobhead · Jun 18, 2014

davesparks said:
Wikipedia is misleading, end of!

Get in there and edit it. It’s what Wiki is all about. they don’t give any guarantees to the accuracy of entries.

Southern22 · Jun 18, 2014

Sorry if this is a stupid question so could you hold back on the Electrical Trainee comments, I'm an apprentice so I have an excuse

Is the neutral earthed at various points on all earthing systems or just specifically designed TN-C-S?

telectrix · Jun 18, 2014

Southern22 said:
Sorry if this is a stupid question so could you hold back on the Electrical Trainee comments, I'm an apprentice so I have an excuse

Is the neutral earthed at various points on all earthing systems or just specifically designed TN-C-S?

neutral is only earthed at various points on TNC-S. with TN-S, the star point (N) is earthed by DNO. see page 44 BS7671.

Southern22 · Jun 18, 2014

Thanks mate

Engineer54 · Jun 18, 2014

Southern22 said:
Sorry if this is a stupid question so could you hold back on the Electrical Trainee comments, I'm an apprentice so I have an excuse

Is the neutral earthed at various points on all earthing systems or just specifically designed TN-C-S?

On a TN-S system the neutral is only solidly earthed at the star point of the supplying transformer.

On a TNC-S system the neutral is earthed at the star point of the supplying transformer and additionally at various point's/locations along it's length.

On a PME system the neutral is earthed at the supplying transformer and additionally at multiple points along it's length. On overhead supplies every 3rd or 4th pole. On new underground DNO installations at every joint.

There is a difference between TNC-S and PME, true PME has a far higher specification with regards to the number of N-E points/positions. The TNC-S systems that are commonly found, are generally converted TN-S systems, supposedly in the process of being fully converted to PME....

Southern22 · Jun 18, 2014

Thanks eng didn't know there was a difference between TNC-S and PME. So when they convert a TN-S does the DNO then go back and earth the neutral at suitable points? Can't imagine this would be done at as many points as a specifically designed PME system would it?

Engineer54 · Jun 18, 2014

Southern22 said:
Thanks eng didn't know there was a difference between TNC-S and PME. So when they convert a TN-S does the DNO then go back and earth the neutral at suitable points? Can't imagine this would be done at as many points as a specifically designed PME system would it?

All i can say with any certainty, is that it will be far less than a true PME system. Mainly because of that age old problem ...Money!! It now costs a fortune to dig up whole streets, so things only get done as and when they need too....

Knobhead · Jun 18, 2014

On more than one occasion I’ve seen jointers just sling a rod in to the hole alongside the TN-C-S PME breach joint. Who’s going to know when the holes filled in?

davesparks · Jun 18, 2014

I've seen that more than once Tony, enough for me to have assumed it is standard practice for them to do.

Knobhead · Jun 19, 2014

Not according to the DNO training collage I went to. But they admitted it was a problem convincing their jointers.

tomspark93 · Jun 19, 2014

Tony said:
On more than one occasion I’ve seen jointers just sling a rod in to the hole alongside the TN-C-S PME breach joint. Who’s going to know when the holes filled in?

You mean like this one?:6: This is just outside a new build I'm on at the moment.

Knobhead · Jun 20, 2014

Inspires confidence doesn’t it?

Wingnut · Jun 30, 2023

Crosswire said:
I'm asking what the the relative benefits are of the two different systems. The link could be added by myself or the supplier, it doesn't really matter.

What is important is how this will affect the installation.

Hiya Crosswire. I found this page helpful;

TT Earthing System: An Easy-to-Understand Guide | Linquip

TT Earthing system: A simple explanation about the TT Grounding system and all you have to know about it is prepared in this article!

www.linquip.com

DPG · Jun 30, 2023

Wingnut said:
Hiya Crosswire. I found this page helpful;

TT Earthing System: An Easy-to-Understand Guide | Linquip

TT Earthing system: A simple explanation about the TT Grounding system and all you have to know about it is prepared in this article!

www.linquip.com