unusual earth- voltage problem

[sparkgap]

Morning all

having read recently a couple of replies regarding earth leakage currents/voltages. I would like your views ( from the experts) regarding my own particular problem.. After inserting an earthing rod for, hopefully, improving reception on my radio receiver, on connecting to the 'earth' terminal on said receiver, I noted a small spark. Measuring this on my AC v meter it showed 62+/_ volts ac ,between radio chassis and earth rod .!!!

The same , of course ? between earth terminal on mains plug, and earth rod.. Further to those earlier replies, does'nt this voltage seem rather high ?? .. Apologies for the 'long winded ' explanation.. Thanks

 

[ProDave]

Assuming your house installation is PME then DO NOT UNDER ANY CIRCUMSTANCES CONNECT AN EARTH ROD TO YOUR RADIO.

A PME earth is effectively earthed at the substation, and may be a few volts different to local earth, hence the current flow you are seeing.

BUT the problem comes if there is a fault. A common fault with a PME supply is corrosion of the outer neutral of a split concentric cable. If that happens, then your radio receiver, via it's mains lead, and your earth connection can suddenly carry a VERY large current, the entire current being used in your house at the time.

This is a well known issue for radio amateurs. Many of them disconnect the local PME earth in their radio shack, and earth everything instead via a substantial earthing rod and earth cable.

But you need to be sure you know what you are doing in that case. Particularly with regard to other appliances in use still on the PME earth, and other things in the radio shack that might still be bonded to the PME earth, like radiators. So don't make any changes to your earthing unless you know what you are doing.

Another alternative for an RF earth, is connect it to the receiver via a capacitor. The capacitor will have negligible impedance at RF frequencies, but a very high impedance at 50Hz. You will need a good high voltage rating capacitor if you try that, in an insulated box to prevent accidental direct contact to the the RF earth.

Yet another alternative if you are using a long wire aerial is a ground plane wire or counterpoise. This is an insulated wire that you run along the ground as far as you can, but never burried and never in direct contact with the ground. Because it's not a direct earth no 50Hz fault current will flow down that.

Remember the requirements for an RF earth for a radio, are very different from an electrical earth for safety.

Tell us more about what this radio is and what sort of aerial you are using. I'm sure I'm not the only radio ham on this forum that might be able to advise you.

 

[steptoe]

Sparkgap, as Dave says, if you have a TNCS/PME do NOT rod your shack. This is well documented in various ham places. I'll explain more later if need be, at work on my phone just now.

 

[nsbs]

As dave mentioned if its a TNCS supply, earth rods are a no-no for the reasons he describes.

ian

 

[Andy™]

60+ volts on earth is quite high. you have a serious fault somewhere. what earthing type do you have? whats Ze?

 

[steptoe]

a quick extract

9 How Does PME Affect the Radio Amateur

The important point from the radio amateur

 

[Manator]

Like steptoe has said above, it would be wrong to describe a step by step instruction on how to do this, the variables and suitability can only be carried out by an electrician with the knowledge of the site visit.

 

[steptoe]

Like steptoe has said above, it would be wrong to describe a step by step instruction on how to do this, the variables and suitability can only be carried out by an electrician with the knowledge of the site visit.

like I said, only he said it much better and clearer. :worship

 

[Petric_Dsouza]

As a beginner Much deligheted to read the entire thread. Happy to be at the right place for useful information.

 

[sparkgap]

Good evening gentlemen,Dave,steptoe,nsbs,Andy,and Manator, .. Please accept my apologies for the late reply(As a new boy , been doing things wrong, by the way I trust it's ok to address you all under the one heading ?? First of all Dave , you more or less summed up things in the first couple of sentences.. I do indeed have PME installed as you rightly assumed, and that in and of itself states the reason why 'earth rods' should NOT be installed ( you were all agreed on that score), and the fact duly noted ..

As a point of interest (maybe ?) The equipment in question is a communication Tranceiver , with built -in A/C power supply(NOT the switch mode type) The antenna is a 'Zepp' type (Doublet ) no radials, no counterpoise. in other words , no connection to earth (by direct means !) All relevant remarks noted ,gentlemen and Thanks ,steptoe,for the extract from IEE Regs.. (more enlghtenment ! ) in fact , thank you all for your input.. I tend to agree, there would appear to be a fault somewhere; -63 a/c/volts , surely a 'bit much'. So, because it is rather difficult , to assess a situation , not being 'on-site' as it were, I will at some time soon, ask a local elecrician to check the system for any possible fault ... Again my sincere thanks to you all, and my best wishes

 

[steptoe]

Sparkgap, that is NOT an extract from the electrical regs, rather an extract from some amateur radio guidance notes I have.

I will try obtain the source if you need further clarification.

There is another quite important document regarding this also, unfortunately Im not in a position to post that just now, sorry.

 

[Manator]

Just to elaborate a little, Earth is a much misused term, understanding of potential differences. from one point of Earth to another is fundamental in understanding why any differences in any current can flow from one to the other. Which is why we often get the debate about exported Earth. A qualified electrician can do some basic tests and give you a solution to your problem.

I visited a property this week that was a DNO installed PME system, and TT to the untrained eye. The rod was connected to the neutral before it entered the property, the previous electrician who visited saw the rod and assumed that the installation was TT.

We all know what happens when we assume anything!

 

[steptoe]

WOW Manator!

A proper PME/TNCS, did you get a picture, that is a very rare beast indeed!

 

[sparkgap]

Hi steptoe, thanks for the correction,re the assumption on my part about IEE. My apologies,'must pay more attention'..

Still, useful however, and if if necessary, will 'toddle off' to the local library, for an in depth read, or of course make a nuisance of myself and 'get in touch with you blokes , ' hi ......... Best wishes

---------- Post Auto-Merged at 14:21 ---------- Previous post was made at 13:44 ----------

Hello Manator, and thanks for the further observation, re the 'misuse 'of -Earth-and potential difference.! I must confess, I have only ever taken the term ,'going to earth' in radio sense at face value. i:e, when knocking up a piece of gear, to me, common chassis is earth, and all other components, which require a positive or negative potential.. Again, I must confess, the nitty gritty of Electrical engineering is beyond me, hence my 'cap in hand ' approach , if anything untoward happens , what is more I had no idea what DNO means, - I looked it up and the only reference I could find was Distribution Network Operators.. Something which is quite beyond me ... Thanks again .. best wishes

 

[Manator]

At least your asking all the right questions, the knowledge gained from these posts will also help you understand what is going on. As for radio, well I know earth is used as a term, and so is ground. I am however a complete novice when it comes to anything radio.

 

[steptoe]

One of the major issues in radio is concerning your masts and ground planes, in an ideal world these should be connected to/in the general mass of earth, ie; the ground.

Unfortunately if you have a PME/TNCS earthing system then you should have them isolated from the ground, as these are connected to your rig, this is where you can end up with different electrical potentials on your metalwork.

If you really want to do this properly Im sure with the help of some of our members here we can help you,

Although you will more than likely need the services of an electrician who understands this type of scenario at some point.

BTW, I am not a ham, but many moons ago i did do a bit of DXing on sidebands using a President McKinnley and a home made antenna, I got S,America with a homemade 1/4 and botched up groundplanes, standard 5W output too,! No burner!