Earth rods

[Robin Spark]

Hey guys,

might seem a silly question, but how often should earth rods be inspected? Obviously I have got GN3 with the recommended time intervals for various types of property, but i was just thinking that something which is outside and can easily get damaged but yet is so critical for safety it should be inspected fairly regular and 10 years on a domestic is a long period of time.

 

[steptoe]

personally, I usually put 5years on a PIR anyway,

and use some judgement on the current condition (and occupiers) as to how to vary it.

 

[Sidewinder]

As far as I can remember there is no requirement to undertake formally recorded inspections on earthing arrangements between PIR's/EICR's.

 

[Robin Spark]

Blimey that was a quick response! Steps you got in first their as well

Ok next question if you dont mind.

Minimum size earthing conductor if both properties either side (domestic) have been converted to PME (according to sticker on cutout). Would you follow table 4.4 (ii) or would you put in 16mm2

 

[batty]

Have used them a couple of times much better than the MK cover jobbies and a lot less likely to get damaged, but i think it all depends were rod is placed as to whether its likely to get damaged.

 

[steptoe]

I always use 10mm minimum, but it doesnt hurt to use some 16mm,

its not going to break the bank,

you will know if they really are PME if you do a Ze on the rod.

 

[Sidewinder]

Me, at least 16mm sq.

Regs may differ!

I use 16mm sq for earthing & "main bonding conductors" as much as possible.

 

[steptoe]

I think he has got himself mixed up with the bad points of PME/TNCS if your neighbour has TT,

Robin, the fact your next door has PME will actually help you install,

 

[Sidewinder]

Steps,

That could depend on the plumbing!...

 

[Robin Spark]

Reason I am asking is that current earth rod is in garden border and rod box is smashed and Ze just over 190ohms, which i am assuming will be alot higher during dryer weather conditions, also the rod is buried below the ground and not in the greatest condition.

So when I go and put new earth rod in, if the street is genuine pme then Steps you are saying I should have a much lower Ze than if it was TNCS.

I'll let you guys know tomorrow the outcome. Thanks

 

[steptoe]

if it really is PME then you 'should' be able to measure a path back to star point via one of the PME rods.

Ive seen readings as low as 1 ohms .

@sidey, yes, could be an issue, still, it wont affect our TT install, Id be more concerned being the TNCS householder if next door TT'd on me.

 

[steptoe]

oh, BTW,

canoey is correct, you still need to test Ra,

testing Ze will only show you if they have actually changed the street to PME or not,

its not the correct way of testing TT.

Ra first to prove your rod is good,

then I just do a Ze to be nosey and see what its like. :C

 

[Robin Spark]

Never actually done an Ra test before, however Megger Mark has just sorted me out with the FLuke 1654b (cheers Mark) which can do this test, however i havent ordered the lead set with spikes for Ra testing yet.

Reason I havent thought about ordering them is the practicality of placing the earth spikes at least 10 metre away from earth rod as per GN3. Ok if you're on a farm but not so easy on an housing estate.

 

[Robin Spark]

You dont need a lead set or stakes, you can improvise very easily....You need to go 10 x the rod length - the fluke manual shows one test (from memory) - whereas you should do the intermediate rod test 3 times with +/- 10% and take the average of the three

Basically you'll need to use your judgement if theres house's, tarmac and concrete involved

Thanks Canoe,

I havent really looked at the manual yet (oops naughty me) as I have upgraded from a 1651 so know how to use most of the functions, however will probably do the same as what i did with my 1651 where I printed the manual out and then got it comb -binded at the local stationers

 

[wozz]

GN3 says roughly the rod should be installed at the time for the rod, therefore the rest of the time it should be better.

 

[Robin Spark]

GN3 says roughly the rod should be installed at the time for the rod, therefore the rest of the time it should be better.

Hi Wozz, your statement doesnt make sense :C

 

[Robin Spark]

Hi guys put rod in today, Ze was 99.4 ohms. Its only a very small estate so do you think this is more likely TNCS based on my Ze or is it too difficult to tell?

 

[steptoe]

I would say its NOT PME

IMHO anyway. :slap

---------- Post Auto-Merged at 18:24 ---------- Previous post was made at 18:23 ----------

99.4 ohms would just be a decent reading back to star point.

 

[Robin Spark]

What was Ra​ out of interest ?

Hi Canoe,

I looked on the cd rom manual this morning and couldnt see an alternative method of using only 1 spike and lead set so didnt try and make something up that I was not sure on. Therefore I only did Ze. But I am going to get a spike set soon without a shadow of a doubt so i can make full use of my mft.

 

[steptoe]

get yourself another rod and cut it in half, might be cheaper than buying proper spikes(?)

with my meter I have the choice of 3 or 4 wire Ra testing.