Can I add earth rods to my incoming setup?

[mattylad]

Hi guys & gals.

My incoming is providing the earth by a clamp on the outside of the cable.

I need additional earthing for amateur radio equipment, for an RF ground.

As much as sinking a bath, wire meshing etc underground would be better I am restricted to only having space for 5' earth rods in my 1855 terrace house cellar.

So if I drive a few earth rods in, join them together using 4mm cable and take that up to the radio it is possible that this earth and the mains earth will be joined at some point as the RF earth will go to the radio but the radio will be connected to the PC which uses the mains earth.

So I can see that there is a possibility of a potential difference and I suspect that I should also connect the RF earth to the mains earth.

Can I do this with the way my incoming mains is earthed?
If joined should this be at the incoming cable point or at the PC?

Any recommendations?

FWIW earth rods provide a poor RF earth but I think that they are all I can do.

 

[JohnW2]

I need additional earthing for amateur radio equipment, for an RF ground. ... So if I drive a few earth rods in, join them together using 4mm cable and take that up to the radio it is possible that this earth and the mains earth will be joined at some point as the RF earth will go to the radio but the radio will be connected to the PC which uses the mains earth. So I can see that there is a possibility of a potential difference and I suspect that I should also connect the RF earth to the mains earth.

You actually have no choice. Your earth rods would count as 'extraneous-conductive-parts (liable to introduce true earth potential - which, as you say, could differ from your installation's 'earth'potential) - and, as such, have to have 'main protective/equipotential bonding' (to ensure that those significant pds can't exist between the two 'earths'). That would require a cable of at least 10mm² CSA joining the earth rods to the Main Earthing Terminal (MET) of your electrical installation - often an exposed block near to your CU - or the earth bar within the CU may sometimes be used as the MET.

Thinking laterally, if getting a decent RF earth for your amateur radio equipment is difficult, have you considered (if it is appropriate) the possibility of using a ‘ground plane’, rather than a true earth (only really feasible for fairly high frequency bands)?

Kind Regards, John

 

[mattylad]

Cheers John, as I don't have any 10mm cable can I just use several 4mm cables from the nearest rod?

Although 10mm is likely the current requirement, the incoming is around 4mm.

 

[JohnW2]

Cheers John, as I don't have any 10mm cable can I just use several 4mm cables from the nearest rod? ... Although 10mm is likely the current requirement, the incoming is around 4mm.

Per regulations, there seeds to be a bonding connection of at least 10mm² from MET to each and every one of the rods (i.e, in effect, the connections between them also needs to be of that CSA). Although not ideal, 3 x 4mm² cables in parallel would theoretically be OK. However, 10mm² G/Y cable is not very expensive, so it might be better to do it 'properly'.

Please also see the paragraph I added to my previous post after you had posted this one!

Kind Regards, John

 

[EFLImpudence]

My incoming is providing the earth by a clamp on the outside of the cable.

If, as suggested, it is TNS you may be able to use smaller csa but 6mm² is the minimum allowed.

 

[mattylad]

A ground plane.... or counterpoise for a wire aerial would be great - if I had room to do so

This is all a maybe as I have yet to figure out how to get coax from out back into the living room, having 22" walls and solid floors make it no small task.
Cheers guys.

 

[bernardgreen]

With most ground rods the impedance rod to soil is high enough to limit the current to be that which a 4 mm ² copper conductor can carry even if the incoming "earth" rises to 230 volts ( as in a failed neutral in a PME system ).

With a very low impedance ground rod / mat system currents from incoming earth to ground rods can be very high. In extreme cases the bond wires have melted and caused fires when metal theft removed the Neutral.

If the bond wires fail then the "earth" to ground currents are going to flow via equipment earths.

That said in your case the incoming earth appears to be from the sheath of the supply and is therefore likely to be a true earth and not derived from the supply Neutral. But a later upgrade of the supply may change this to an "earth" derived from the Neutral.

At hilltop radio sites it was often necessary to totally isolate the incoming ( supply ) "earth" from the station's true ground. Often the supply "earth" went only as far as the inter winding screen in the supply transformers.

 

[JohnW2]

A ground plane.... or counterpoise for a wire aerial would be great - if I had room to do so

Fair enough. It's certainly frequency dependent - I've done it (with wires) on 10m and above, but it would get impractical for most of us at lower frequencies than that.

This is all a maybe as I have yet to figure out how to get coax from out back into the living room, having 22" walls and solid floors make it no small task.

I know that problem! In through the roof (under the eaves)??

Kind Regards, John

 

[JohnW2]

With most ground rods the impedance rod to soil is high enough to limit the current to be that which a 4 mm ² copper conductor can carry even if the incoming "earth" rises to 230 volts ( as in a failed neutral in a PME system ).

That's true, but as EFLI has said, 6mm² is the absolute minimum allowed by regs for MPB, and most people would probably use 10mm².

Kind Regards, John

 

[mattylad]

John, I'm in the living room at the front of a back to back (knocked through) terrace so going out the front wall and over is 35m+ of coax, going through the house is hard because I cannot get from A to B as my floor is 6"+ of solid stone, the internal walls are 14" thick and I can't drill through to get to where I need.

This also causes me issues with getting a good ground, using the mains earth (which itself is through an extension lead) is absolutely not good enough.

I suspect I may be adding another socket outlet or two in the wall, luckily its a plasterboard over old wall in the chimney alcove construction so may be possible to come up out of the cellar and have a brushed plate.

All via the cellar, then through the middle floor to the back wall where a big hole will be drilled.

This then brings me back to the RF earth, with big stone slabs in the cellar, outside on the back pathway and no garden all I think I can do is put rods into the little bits of mud I can find.

Cheers.
Matt

 

[JohnW2]

John, I'm in the living room at the front of a back to back (knocked through) terrace so going out the front wall and over is 35m+ of coax, going through the house is hard because I cannot get from A to B as my floor is 6"+ of solid stone, the internal walls are 14" thick and I can't drill through to get to where I need.

Fair enough - I've had much the same problems myself! Mind you, 35m of coax would not necessarily be the end of the world, if it were decent low-loss stuff.

This then brings me back to the RF earth, with big stone slabs in the cellar, outside on the back pathway and no garden all I think I can do is put rods into the little bits of mud I can find.

Good luck. I can't say I've ever tried an RF earth under a building, so I'm not sure exactly what you can expect!

Kind Regards, John

 

[bernardgreen]

That genius Russ Andrews has solved your problems with earths


//www.diynot.com/diy/threads/more-russ-andrews-guff.409919/

 

[mattylad]

well at least I have some info for what to do if and when I can add some rods.

Cheers.

Now I just need to come up with the antenna solution

 

[JohnW2]

Now I just need to come up with the antenna solution

That would obviously help What band(s) are we talking about?

Kind Regards, John

 

[mattylad]

80 & up.

I have bad QRM from 40 down but 20 is excellent on a g5rv jnr.
Although this causes major RFI to the attic dwelling student type ogre's speaker systems & keyboards etc. (truckload of clip on ferrite has been purchased).

But I want to put it much higher and for the lower bands, possibly multiple wires.
Problem is that I have 55' from chimney down to the back of the property.

So am going to sacrifice a 10m fishing pole on T/K brackets on the rear of the house so a multi element sloper (1 per band) may be what I need to do.
http://www.mds975.co.uk/Content/amateur_radio_antennas_04.html has lots of ideas, the main problem being as said above - getting coax from A>B.

Am off to a rally in Sale in the morning to get some bits, a center & some insulators - a balun if I see one cheap enough etc.

Although my best use is when mobile at the Haslingden Halo site (google it) and using a random long wire. (also no QRM).

Cheers,
Matt