Why would someone rod a TNS installation

[NozSpark]

I was doing a CU change the other day and found that someone had installed a rod and connected it to the MET....WHY????

There was no problem with it, the Ze was 0.21ohms...

ok the block might have been loose, you know where they just screw the block over the top of the plated copper band, but that was easily fixed (trim, fold and stick in MET hole)!

 

[steptoe]

lots of reasons,

dont knock it til you find out why,

or not,

perhaps it was rodded temp and the TNS was re-instated,

you want to see my house!

or maybe not, :slap

 

[NozSpark]

Old original plated strap around the PLC incommer... not been touched since it was installed!

and it's only a domestic bungalow,, pretty bog standard

 

[steptoe]

I have a TNCS with a rod or two installed,

Im dying to get a DI to PIR it just to see what he would make of it.!

EDIT, NOZ, nothing intended, just out of interest,

BTW, Im thinking about this, and ATM I cant think of any reasonable reason why someone would rod a good TNS,

I'll get back to you if something comes to mind.

 

[NozSpark]

Code 1 mate

Isn't mixing earthing methods against regs?

Don't know though, don't have regs to hand or even imprinted in my brain...

No offence taken mate, I know what you mean, some DIs just don't have a clue

 

[PC Electrics]

Code 1 mate Isn't mixing earthing methods against regs?

This has been said to me many times, but I've yet to find an actual reg which forbids it.

Don't know though, don't have regs to hand or even imprinted in my brain...

No offence taken mate, I know what you mean, some DIs just don't have a clue

Well, I'm a DI.

I would test the rod for Ra (if it's installed it should be effective [1]), note it's presence and Ra in comments and leave it at that (no code). That okay?

[1] a bit like your spare tyre in your car - it's not a legal requirement to carry a spare at all, but if you do it must be 'legal'

 

[wozz]

ok how about this.

Work carried out at the house, TNS reading found to be too high, DNO informed and take a look, say they will take action but rod it in the mean time, rod installed, Earth cable stays on sheath as its extraneous, DNO carry out works Ze drops to within limits again.

Doesnt sound that strange to me?

 

[Andy™]

look at it this way. if there was a metallic rod sticking out of the ground, you would have to bond it because its extraneous....

 

[NozSpark]

There's a thought....

Only thing is, it's outside so that wouldn't be within the equipotential zone!

Oh, and Wozz..... No RCD!

 

[Larnacaman]

Most Council house estates in the early 50s were generally provided with an aux rod or small latticed mat on TN-S supplies!! Don't know why, but can't see a problem either. Same as there wouldn't be any problem having a local rod connected to the MET of a PME supply system, in fact quite a few countries, including Ireland i think , insist on it!!!

If you think about it, would you remove a good valued rod on a TT system that had, had it's supply PME'd?? I certainly wouldn't....

 

[M107]

Round here BG contractors at a few properties have been putting in rods to bond the gas service pipework. This is after inspections by BG & they have picked up MEB to gas as being non-existant/undersized.

 

[Andy™]

Round here BG contractors at a few properties have been putting in rods to bond the gas service pipework. This is after inspections by BG & they have picked up MEB to gas as being non-existant/undersized.

i even have a pic of something like that!

 

[M107]

Yes thats much the same as I've seen....with the exception on a few of the properties the 10mm gas MEB is on the pipework inside the building...I know because I've installed it.

 

[Sidewinder]

So, now you could have a pme system trying to earth diverted N currents through the gas line to the earth rod, &/or you could have a different earth potential between conductive parts within the property as they could be connected to two different earthing systems.

Or, there could be no problem...

 

[Larnacaman]

So, now you could have a pme system trying to earth diverted N currents through the gas line to the earth rod, &/or you could have a different earth potential between conductive parts within the property as they could be connected to two different earthing systems.Or, there could be no problem...

If your talking about a bona fide PME system, ...i think you'll find it's the latter!!!

 

[steptoe]

So, now you could have a pme system trying to earth diverted N currents through the gas line to the earth rod, &/or you could have a different earth potential between conductive parts within the property as they could be connected to two different earthing systems.Or, there could be no problem...

just imagine,

nice sunny day, you are out hosing the garden at the back of the house, fault appears on PME, gas rod at the front door picks it up, pulls it back inside the house and cross bond to the water, you go to turn the outside tap off in your bare feet on a wet lawn! bad day explode

 

[Sidewinder]

Come on peeps, serious polite debate, hence my elipsis (...)

LM, you are correct.

Steps, you are correct.

As you both know...