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?

 

[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.