Earth stake fixture

Think I’m going to get this little honey for my spur very soon. Great idea don’t you think. Yes that’s the same 50 mm square as my earth wire. Pls remember this is suitable for the New Zealand market and in no way would I suggest for any member to go outside your own country’s regulations. I’m just sharing that’s all

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These can be used for TT earth setups. In much of Europe most recent housing or relatively recently refurbished housing has PME earth setups, and as such one can’t use your suggestion unless you convert from PME to TT. You can’t mix PME and TT earthing systems into a single earthing system without causing potentially lethal consequences or risks of fire in utility fault conditions. In much of Europe you would also most likely invalidate any insurance.

If using and relying on or having installed a TT setup one should check your earth electrode ground conductivity and potentially adjust your RCD devices to compensate. An electrician will know about this.

I do use a TT system in the UK for my house… and yes it provides a lower noise floor on my earth than my previous PME system.

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Simon - i take it the change to TT from PME was related to your other (RF related) interests with a subsequent benefit for the Hi-Fi ?

Absolutely… and if am honest if you can I would recommend paying to convert from PME to TT in many setups. In rural areas PME setups can be rather noisy, and TT is perfect if you have the space and right soil conditions. It’s a relatively straightforward task for an electrician with the right equipment.

But do remember an Earth electrode is good and dissipating low frequency switching noise … it has very little if any effectiveness for most forms of RF interference. along with any mains grounding system. Many people seem to get confused by this and there is lot of false information on the web.
As such it can be quite a popular topic in radio engineering and operating exams.

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Yep - inductance is usually too high to be effective at high frequencies for the casual earth wire advocates. We’re urban based at the moment so PME is effective enough but when we move out to a more countrified area then we’ll certainly consider a switch to TT if we can.

James… it’s not that… it’s all about the wavelength and coinciding with a voltage peak… if the point of optimum earthing does not align with a wavelength RF voltage peak point, then the earthing has less effect. If the point of optimum grounding occurs at a RF voltage zero point, it will have no effect at all. A frequency of 30 MHz has voltage zero points at 0, 5 and 10 metres (recurring) and maximum earthing at 2.5 and 7.5 metres recurring.

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Yes good point Simon - It’s still the weekend so i usually disengage my brain !

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30 years ago the my new build had PME installed but the electrician still put in an earth rod. At the last electrical test the electrician remarked that the earth impedance was remarkable low. I assume my installation is safe! The earths are daisy chained with one of the existing two CUs having the earth rod.

I am contemplating adding a third CU for my existing dedicated hifi radial. I am not sure if the electrician will want to disconnect the earth rod, but they do want to replace the existing earth wire from meter box with 3 new earth wires.

I am wondering whether i might loose something SQ wise if the earth rod is removed. Any thoughts?



Hi Filipe, as described your setup does not sound safe, and I would expect nullify your buildings insurance… you must not combine a PME and TT earthing system within a single earthing system, the consequences are potentially lethal and/or destructive if a fault should occur with the utility supply… essentially should a fault occur with utility and the supply neutral goes open circuit then the substation/distribution transformer current would pass through the point of lowest impedance to earth which could be your domestic wiring and earth electrode causing a melt down of your mains wiring, a fire and damage to your house, and potentially unsafe potentials across metal fixtures in your house during the fault causing electrocution.

If you have outbuildings or static caravan a physical distance from your main PME supply, then these external structures can be validly earthed as TT… that is using an earthing electrode and the supply PME earth is separated

I suspect if your qualified electrician has installed a proper low impedance electrode you either have an outbuilding or separate physical earthing zone for one of your CUs (with a physical separation of several metres between fixtures), or in fact you have TT earthing as opposed to PME actually enabled.
If you do have separated earth zones then you must avoid any cabling, earthed Ethernet, coax, metal water pipes etc between the zones… there should be a warning about this on the installation.

As far as SQ, your PME utility earth might be electrically noisy with low frequency noise with respect to live and neutral… especially if some distance from the substation. Converting to TT can usually remove this within your earthing zone.

To sink RF voltages a different technique is required in conjunction with your safety earth electrode… you need a large buried metal grid of several metres across dependent on wavelengths or you need to tune a system of hub and spoke electrodes … where the spokes are calculated for the wavelengths of interest… I use the latter.

Most of these in NZ get knocked out by lawn mowers and strimmers!!

Hello Simon, Thank you for your reply.

We are less than a mile as the crow flies from the substation by overhead poles. The final leg is about 50m in a trench. I can remember talk of PME depending on whether there was an overhead pole earthed in sufficient proximity to us. Just to confuse matters, another building off the same final pole was converted for residential use about 10 years ago and was not labelled as PME! The next pole (also on our property) has what I assume to be an earth cable running down it. To my knowledge ours is the only nearby supply with a PME installation off that pole.

Our earth rod is close to the incoming supply. Being by an outside wall it would have needed a hole drilling into the 2m deep foundations, unless it diverted underneath the concrete path!

So if I went ahead and added a HiFi CU would it be advisable to first get Western Power Distribution to remove the PME and test the adequacy of the earth rod?

I now have a circa year 2000 552/500 serviced late 2016. When I got it the 500 PS hummed quite loudly. Before it was the 555DR PS, but that stopped humming when the 500 arrived. Since the arrival of the 500 the hum has lessened to the extent that although I hear it it is not intrusive except when certain appliances are on when it becomes quite loud.

Soundwise the whole system has improved over the 6 months I have had the 552/500. The bass is a real joy and instruments are so clear with proper soundstage. Obviously nothing muddy soundwise, although some times are better than others. So I have wondered about whether the separate CU is needed. We have no near neighbours electrically.

Advice welcome. Thanks in advance.


Yes - and given what your neighbours appear to have done - that sounds eminently sensible.

I think it unlikely a seperate CU will make much if any difference unless of course you need more space for RCDs etc

Thanks again. I will contact Western Power Distribution.

Why do think the separate CU would not improve anything?

I have wondered about whether there would be any benefit. In some respects I can control what electrical devices are on, and do in fact turn unnecessary stuff off so the noise they might introduce is not present. I have metal CUs also.


What are you looking for it to improve?
Electrically they will most likely be connected together with very low impedance thick wiring over a short or very short distance.

Other people on the forum say without a separate CU SQ will not be improved by the dedicated radial I have.


Ok give it a try… I personally think adding a separated CU will provide minimal impact if correctly installed.

@Simon-in-Suffolk Thanks Simon, I think the first step is the removal of PME. Phil

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Just had a visit from Western Power Distribution who contradicted the advice about mixing TT and PME saying the 18th Edition of UK regs allows it and it is recommended at least by WPD that earth rods are also installed with their PME.

He said that the RCD will chop the supply in the event of a supply fault. May fry some electronics though in some circumstances! Can anyone elaborate?

He said I could opt not to use the PME if the electrician checked the adequacy of the earth rod. So will things be better if my electrician removes the PME after checking in dry weather the quality of the TT? We have lots clay which I assume when wet is a good conductor. The earth rod is under a concrete path which should keep the ground moister.

Still bemused about the contradictory advice on the benefit of a separate hifi CU.



Regarding the CU. It depends on your existing setup if you need / want to do this. The main benefit of the dedicated radial is the unbroken run of cable between the CU to the socket, rather than the daisy chaining of multiple sockets on a ring. The separate CU would also allow you to run a non RCD protected radial (in the 17th edition regs) now not allowed in the 18th edition. Most CU units are pretty full with the house circuits so may not have enough room for additional circuits for the Hi-Fi. Me, i went the separate CU route - not enough room in the existing box and i was only going to do the job once so went the route that i thought would be best.

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Yes … talking different things… the RCD protects your internal circuitry and you by disconnecting live and neutral if there is an inbalance between live and neutral currents; ie current is leaking to earth for an appliance on your ring or spur.

The earthing system is all about the supply and earthing entering your property or implemented at your property… nothing to do with live and neutral within your property. If there is a fault on PME it’s the earth that can become problematic if locally grounded to low impedance earth stake not the live and neutral within your house.

As far as opting not to use PME, that all does sound correct… in the UK to be signed off your earth electrode(s) has to be installed tested by your electrician to meet minimum conductivity requirements. Your electrician will likely advise you of this when undertaking the job.

Clay has usually good conductivity … a 2 plus metre electrode (they often screw together) into shaded earth with a clay subsoil is often ideal… even better if your water table is not too far away.

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