Why the need for an earth spike test kit?

[HappyHippyDad]

I am about to put in a copper rod to TT a garage.

I have a megger 1731 but do not have the Earth spike test kit.

I will be able to test the Ze once the rod is in place and wondered what the difference is between testing the Ze and testing the Ra with a spike test kit?

Is it sufficient to just test the Ze rather than purchase a test kit to test the Ra. Will the result be the same? I.e. Ze = Ra

I'm not entirely sure if my terminology is correct, I know Ze is for the external EFLI and am assuming Ra is when you use a test kit rather than the live test?

 

[westward10]

Ra is the sum of resistances of the electrode and earthing conductor and does not include the line resistance as Ze would. Ze is measuring the earth fault loop path, Ra is only measuring the electrode and earthing conductor.

 

[Deleted account]

Personally for a garage I dont think you need to. I always just stick the rod in and Ze it.

If your not happy with the read stick another one in.

 

[Strima]

Carrying out an EFLI test (test method E3 in GN3 page 64) on a rod is an acceptable method.

I only used spike kits on new installations where there was no supply available and for initial verification.

 

[davesparks]

Carrying out an EFLI test is acceptable if RCDs are being used for fault protection for all circuits.

 

[Dustydazzler]

I haven't seen anyone use a proper earth electrode tester on site since the 1990s

To be honest I don't think any new sparks would even know what to do with one

 

[richy3333]

We Ra test all the time.

@happyhippydad I might have a spare Megger Ra test set if you want it. 3 sets of leads and the probes. Just PM me and I'll search it out of the storage box

 

[Dustydazzler]

Now that's an offer you can't refuse

 

[HappyHippyDad]

We Ra test all the time.

@happyhippydad I might have a spare Megger Ra test set if you want it. 3 sets of leads and the probes. Just PM me and I'll search it out of the storage box

Richy, that's really kind of you
I'd love to have it to have it but only if you are absolutely sure you're not going to need it (have a proper think). Also, I'd want to give you something for it..... money, beer, whiskey or something to charity (plus postage)?

 

[HappyHippyDad]

Very nice people on this forum (looking for a 'humble' smiley, but can't find one).

 

[JK-Electrical]

I haven't seen anyone use a proper earth electrode tester on site since the 1990s

To be honest I don't think any new sparks would even know what to do with one

This video should help any such new spark ....

​

 

[HappyHippyDad]

My Megger earth spike test kit has just arrived from @richy3333 .
He refused all payment, even postage.
What a top chap .

 

[westward10]

Top man Richy.

 

[richy3333]

Please you'll make me blush. Its always good to help each other out in the trade

 

[HappyHippyDad]

We have thunder and lightning here.... however, I have a new toy and have just been in my garden to experiment! Popped my spare 5/8" rod into the ground about 9", positioned the potential and current electrode correctly (in the pouring rain with a smile on my face) and pressed play! 180ohms.

I then hammered in it to about 15" and it went down to 96ohms.

This is all very exciting!

I darn't hammer it in any further as I did that in my garden as a practise when I first started out some years back (thinking I could just pull it out afterwards) and I had to dig a big hole to get it back out.

 

[HappyHippyDad]

This method of testing the earth impedance has got me thinking.
Ze ≠ Ra.
If we had a Ze of 150Ω on a TT this is measuring the earth fault pathway including the line conductor. Is the Ra likely to be very similar as the impedance of the line conductor is likely to be extremely low?

 

[davesparks]

This method of testing the earth impedance has got me thinking.
Ze ≠ Ra.
If we had a Ze of 150Ω on a TT this is measuring the earth fault pathway including the line conductor. Is the Ra likely to be very similar as the impedance of the line conductor is likely to be extremely low?

Yes and no, in theory they will be very similar yes. But the Zs test method will (I think) be more susceptible to the influence of other buried metal objects, such as next doors earth rod(s) and bonded services being in the sphere of influence of the rod under test.

All the earth rod testing I do is 3 wire FOP as it is for generators at events where Zs testing obviously wouldnt work for this purpose.

 

[HappyHippyDad]

Well I used @richy3333 's spike kit for the first time at a customers a few days ago. It did actually save me having to take the cover off of the CU in order to carry out a Ze so no disruption to the customer. It also meant I could test before faffing around with the actually cable run back to the CU. This knowledge could be useful if I had to add another earth rod, although I didn't.

5/8" 4ft rod and I got an Ra of 45Ω . It takes more time pacing around lifting up drains and looking at oil pipe runs to make sure you don't hit anything than getting it in the ground. Saying that, it still took perhaps 5 minutes to get it all the way into the ground and it's still a bit scary hammering a pointy metal spike with a sledgehammer into unknown ground!

I actually changed the Cu in the same property yesterday and the Ze was 44.8Ω so very similar to the Ra, better than the 300+Ω it was before!

 

[Strima]

Cheap SDS Max with a rod driver saves a lot of effort. Just set it to hammer and crack on.

If you're starting to do a lot of rods it would be worth investing in a CAT and Genny and doing a training course, cheaper than hitting an electric or gas supply.

 

[HappyHippyDad]

Cheap SDS Max with a rod driver saves a lot of effort. Just set it to hammer and crack on.

If you're starting to do a lot of rods it would be worth investing in a CAT and Genny and doing a training course, cheaper than hitting an electric or gas supply.

I reckon I'll do about 2 rods p/year so I (hesitantly) don't think it's worth the investment in a CAT and genny. However...... if I did go through something!!!

Does the detection device find anything? I.e pipes (oil, gas, water) and cables?
[automerge]1568748898[/automerge]
A quick scan of the net and I'm guessing a CAT and genny detects metal pipework rather than drains for example?

 

[Strima]

I reckon I'll do about 2 rods p/year so I (hesitantly) don't think it's worth the investment in a CAT and genny. However...... if I did go through something!!!

Does the detection device find anything? I.e pipes (oil, gas, water) and cables?
[automerge]1568748898[/automerge]
A quick scan of the net and I'm guessing a CAT and genny detects metal pipework rather than drains for example?

They will detect active services such as electrical cables with current flowing but it takes practice to understand the results as gas and water for example would appear as voids especially with the prolific use of MPDE pipes. If you have a power supply that is timed, such as remotely supplied street lighting, you'll only find out when the lights get turned on and there's a big bang... ?

The genny is only used when tracing a known cable, you put current down it and trace it with the CAT.

 

[UKMeterman]

I reckon I'll do about 2 rods p/year so I (hesitantly) don't think it's worth the investment in a CAT and genny. However...... if I did go through something!!!

Does the detection device find anything? I.e pipes (oil, gas, water) and cables?
[automerge]1568748898[/automerge]
A quick scan of the net and I'm guessing a CAT and genny detects metal pipework rather than drains for example?

As I have worked for Radiodetection, you can get a unit to fit on a push rod, the cat can then follow the unit above ground.