TT testing.

[La Poste]

If testing a TT installation which tester would you prefer?

The Earth resistance tester or an earth fault loop impedance tester.

I mean if you were to test with an earth resistance tester (the inserting spikes in the ground test) and get a value for Ra, would this value be the same value that you would get if did the same test with a loop impedance tester, testing live between the line and the rod?

I just wonder.

Thanks.

 

[ruston]

Not much ground around now in most places to use the Earth resistance tester now , especially in the domestic scene : Well the ground is still there but you can't get at it lol.

 

[Deleted member 26818]

Unless you're installing PME points, or attempting to get a reading low enough to allow RCD protection to be omitted, where a degree of accuracy is required.
There's not much point in using an electrode resistance tester, just use your EFLI tester.

 

[Engineer54]

If testing a TT installation which tester would you prefer?

The Earth resistance tester or an earth fault loop impedance tester.

I mean if you were to test with an earth resistance tester (the inserting spikes in the ground test) and get a value for Ra, would this value be the same value that you would get if did the same test with a loop impedance tester, testing live between the line and the rod?

I just wonder.

Thanks.

You'll always get a more accurate value with a dedicated earth test kit than doing and EFL. Just that, sometimes as been stated you don't have the space to conduct a earth resitance test, unless the clients have good neighbours.

You really do need a good distance between the current spike and the electrode under test and between the current and voltage spikes to get good meaningful readings. There are alternative methods you can employ when distances between test spikes are a problem, like the Triangle method, but you would need to know what your doing, and what the readings the test instrument are telling you. you may have to juggle the test spikes around a bit before getting a decent reading value.

 

[Engineer54]

If testing a TT installation which tester would you prefer?

The Earth resistance tester or an earth fault loop impedance tester.

I mean if you were to test with an earth resistance tester (the inserting spikes in the ground test) and get a value for Ra, would this value be the same value that you would get if did the same test with a loop impedance tester, testing live between the line and the rod?

I just wonder.

Thanks.

No, is the quick answer!! lol!! Loop test will give you quite a rough value, of the true earth rod/electrodes Ra value... But as you only need 200Ohms in the UK it matters not a jot!! lol!!

 

[La Poste]

This seems to be a good budget tester but good for experimenting with.

http://www.test-meter.co.uk/index.p...=516&utm_source=GoogleBase&utm_medium=organic

I'm really tempted to buy it just out of curiosity.
My friend has a TT system with multiple rods at his workshop/ farm.
It would nice to have a test or two and compare the difference with my EFLI tester.

What do people think of this tester?

 

[D80]

Got many TT systems that would justify the expense?

A lot of TT systems around here, but my MFT Loop Tester is my preferred test method. 1 less tester to calibrate too. Would probably get some odd looks banging extra spikes in too.

Only ever used the dedicated tester once, when I was an apprentice a decade or more ago.

 

[ruston]

If you want to buy it to enhance your understanding ,then its fine. But I doubt you will get any payback on it for the reasons stated by Spin and E54.

You must be another one that loves the gear lol.

 

[La Poste]

You must be another one that loves the gear lol.

It makes it more interesting.

I hear that if you measure Ra the figure is not linear, Ra increases as you move away from the rod up to a certain distance then does not go down much at all no matter how far you increase your distance from the rod.

Sounds a bit odd to me, although I don't know if it is true.

 

[Engineer54]

Save your money on this bit of test kit, specifications are well below par, hence the low price!!
You'll need to spend at least 300 to 400 quid for a half decent budget test kit i'm afraid..

Different if you did a lot of TT system work in a rural area's, then the extra cash would maybe worth it... To give you an example, our test kit (and it's by no means the most expensive) cost over 2000 quid. It's a ''Null Balance'' earth resistance tester, which i was first trained and brought up on. I would put more faith in our machine, than any digital bit of kit out there... lol!!

 

[johnboy6083]

The distance between the rod under test and the reference rod should be about 60m for the best reading, and the furthest test rodshould be 100maway. Of course in practice this is very difficult, so as long as you keep the 60% ratio, alter the distances to suit.

 

[ruston]

Sent you Link . Take too long to type out .OSG also alludes to the difference in testers. Like these for instance.Megger Earth Resistance Testing

 

[La Poste]

Thanks for the replies, maybe I can hire a tester, it might be the cheapest option, the rods have already been installed by a company that has been and gone, I just want to test them for my mate.

I will have a look this weekend, I just hope they have all been tied together and not installed separately with each fuse board.

I will take some pictures too.

 

[WayneL]

If testing a TT installation which tester would you prefer?

The Earth resistance tester or an earth fault loop impedance tester.

I mean if you were to test with an earth resistance tester (the inserting spikes in the ground test) and get a value for Ra, would this value be the same value that you would get if did the same test with a loop impedance tester, testing live between the line and the rod?

I just wonder.

Thanks.

No, it wouldn't.

Firstly, the 'Earth Electrode Resistance Tester' does what it says on the tin - it measures 'resistance' Ra ......as oposed to 'Earth fault Loop Impedance'. Ze

Secondly, the 'Earth Electrode Resistance Tester' only measures the resistance of the 'Earthing Conductor' and the 'electrode' to earth - it doesn't measure the 'loop' .... i.e. it doesn't include the impedance of the 'line' conductor.


Really speaking, if you were to go by the book, then, on a new TT install (Initial Verification), you should always use an 'Earth Electrode Resistance Tester' .....as this is a 'dead test' and would confirm that you have an adequate earthing arrangement before energising the installation.

 

[Engineer54]

The distance between the rod under test and the reference rod should be about 60m for the best reading, and the furthest test rodshould be 100maway. Of course in practice this is very difficult, so as long as you keep the 60% ratio, alter the distances to suit.

A bit over zealous there with your distances me thinks for a general set up! ...lol!!
Generally the current spike is set at around 50m The potential spike at it's furthest point. will be at 72% of the distance between electrode under test and the current test spike and the shortest at 52%, having first testing at 62%. The 72% and 52% are basically to check that the 62% value doesn't vary, (not in a zone of influence)....

If it doe's vary, then you need to increase distances, or take your test run in another direction from the electrode under test, and start again.

But i can agree with you, in some circumstances, depending on what the size of the electrode system, the terrain and soil resistivity, distances required can become quite substantial. But this is rarely required when a single electrode is being tested.

Then again there are many different ways of testing electrodes and multiple electrodes and electrode earth fields. Earth testing can be a relatively specialised field, once you get past the basic set-up, but not one the majority of electricians will get involved with...