Re: Earthing systems

[Dambo]

Hi there,

I wonder if someone can help with this: Regarding TT, TNS and TNCS earthing systems - What are the pros and cons of each?

 

[Zeespark]

TT is a higher Ze but is alot more useful in terms of equipotential zone compared to the other 2.

AndyGuiness Drink

 

[Dambo]

Why is it a higher Ze?

 

[spinlondon]

High resistance through the Massive Earth. Different resistances due to weather , and soil composition .

 

[Dambo]

Thanks. Do you know what the pros and cons are for each of the 3 earthing systems?

 

[Badger]

Hi there,I wonder if someone can help with this: Regarding TT, TNS and TNCS earthing systems - What are the pros and cons of each?

TNS is by far the best

 

[Dambo]

I'm just in the process of learning about each of the earthing systems though and don't really understand what the benefits and drawbacks of each are.

 

[Badger]

Good points, - TNCS is usually available to most properties, good reliable earth as connected to neutral, cheap way of providing earth to consumers house/property

TNS Seperate Earth supplied but needs another seperate cable installed within the original supply cable. good conductivity to earth readings, reliable.

TT doesnt use dnos earth and can be installed in any property, cheap for dno/supplier as they dont have t worry about it.

BAD POINTS TNCS if neutral is lost in suppliers cable then earth goes,

TT if poor ground/soil/gravel/ then reading is high and needs further earth stakes installing which can be a pain in the ars

TNS expensive for dno to install, and also on older systems the earth connection to the sheath can become corroded.

 

[Dambo]

Top man badger! That makes more sense. Thanks for your help!

 

[a1]

Good points.TT doesnt use dnos earth and can be installed in any property, cheap for dno/supplier as they dont have t worry about it.

They are under no obligation to provide an Earth facility anyway - As you know, Badge.

BAD POINTS

TNCS if neutral is lost in suppliers cable then earth goes,

But they (Especially the new ones) are earthed to ground through certain intervals along the length of the DNO's Supply cable. Aren't they?! :|

 

[Andy™]

TT - earth comes from rod. much higher Ze than TN systems, everything needs RCD. second safest

TNS - earth comes as separate conductor from transformer. Ze under 0.8. true TNS is safest, but these days i doubt you will find a true TNS since it will be bonded to neutral at many points

TNCS earth comes from neutral split at service head. least safest system, but cheapest of TN systems for DNO. another example of money over safety

see first pages of OSG for diagrams and more info

 

[Dambo]

Thanks very much too Andy!

 

[Andy™]

few thing wrong with that admin.....

DNO are required to provide an earth where reasonable, as per ESQCR.

also, if a neutral is lost at some point, then in effect, you may aswell connect your neutral to a rod. your 'earth' will become live and there will be nothing to stop you getting a shock between PME earth and true earth. and your no matter how well your RCD works, its guaranteed NOT to trip!

 

[binky]

BAD POINTS TNCS if neutral is lost in suppliers cable then earth goes,

My NICEIC assessor was telling me about a fault that occurred in Truro (pasty & pixie land) (Cornwall) where by the local gas main became the return path and was glowing red-hot due to 400Amps running through it. 'Cooking on gas' must have been fun that day :^O .