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Im sorry if i have posted in the wrong section, but i wasnt able to find a better one... And im also sorry for taking up your time...

Please excuse my English...It isnt very good.. :(

My problem is this:

I have bought a TV card for my computer and tried to connect the antenna to it. (75ohm/coaxial antenna). The computer was plugged into a non grounded socket. When the antenna touched the chassis of the computer the electric safety switch went off. - i dont know how its called-

Not knowing what the cause was i did some experiments and it seems that the safety switch will go off even if i just connect the pc to a socket that is grounded, without having to come in contact with the antenna.So i guess the antenna plays the same role when i used a non grounded socket..

I have also replaced the computer power source, but the problem still persists.

The sockets that are not grounded seem to have the grounding "pin" attached to the null -i dont know if this is the proper term..im trying to say "the exit" of the socket-

I did some measurements [see atachment]..

Im sorry for my lousy English..

Does anyone have any ideas? :(
 

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Chappers

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  • #2
The safety switch you refer to is an RCBO (Residual Current Breaker with Overload protection) which is a combination of RCD (Residual Current Device) to trip off in the event of current running to earth, and an MCB (Miniature Circuit Breaker) which provides overload protection, and seems to be rated at 32A in your image. The I-delta-n or tripping current of your RCBO seems to be 0.3A or 300mA and since it trips off when you use a grounded socket or connect the aerial coax which is offering an earth potential, that'd imply that your computer is leaking more than 300mA to earth. I found that in Spain many sockets didn't have earth connections, they didn't even bother running an earth wire to the socket outlets and I used to get some nasty shocks from the compuiter case until I remedied the situation by adding an earth. Most computer equipment has earth leakage currents present because of the spike suppression in the SMPS power supply, but I've never found it enough to trip a 30mA RCD, let alone a 300mA one. There are two likely possibilities that I see: one is that the PCs power supply housed in the PCs case is leaking too much to earth, or there is another appliance on that circuit leaking large amounts of current to earth but not quite enough to cause the RCBO to trip until you plug in the PC which adds just enough to send it over the limit and knock off the RCBO.

Others have probably got more suggestions too. Just my two-pence worth.
 
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  • Thread Starter Thread Starter
  • #3
Thank you very much for the reply! I have replaced the PCs power supply, so we can rule this out... i think..
 
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Chappers

  • Thread Starter Thread Starter
  • #4
Have you tried disconnecting everything else fed from that circuit to rule out high leakage current from other appliances adding up to enough to knock the RCBO off? I'd do that, so only the PC is running from the circuit (with an earthed socket being used) and see if it still trips.

You could do with carrying out an insulation resistance check too, to rule out any slight line to earth or neutral to earth short. In my parents' villa in Spain they had nuisance tripping when plugging in some appliances that naturally had some earth leakage currents. In the end I found out why - there was already a degree of leakage to earth taking place before anything else was plugged in, and once something with some leakage was plugged in, it was too much and tripped the RCD. Tracked down the cause just using a multimeter in the megohm range on the isolated circuit, it was a high-resistance short between live and earth which had been caused when too many single core cables had been drawn through the small conduit damaging the insulation on the live and earth cables.
 
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  • Thread Starter Thread Starter
  • #5
Im gonna try that tomorrow. I have tried today with only the lighs on and it still tripped. Im gonna try tomorrow without any lights on...
 
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Chappers

  • Thread Starter Thread Starter
  • #6
As well as the insulation resistance check on the circuit wiring if you have the proper test equipment (or at least a multimeter check for anything obvious), have you tried another mains lead from socket to PC power supply?
 
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  • #7
Yes, when i replaced the power supply i also replaced the old cable with the new one which came with the new power supply..

Thank you a lot for your time! :)
 
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  • Thread Starter Thread Starter
  • #8
Have you tried disconnecting everything else fed from that circuit to rule out high leakage current from other appliances adding up to enough to knock the RCBO off?
Ive made a drawing of how i see the electrical circuit in the house. Can you please tell me how could other appliances-without grounded sockets- use the grounding from another socket? Or where you talking about multiple appliances connected to the same grounded socket? *this is not my case*
 

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Chappers

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  • #9
I was assuming that other sockets did have earth connections, and that the earth connection was universal to those sockets. I'm not sure what you mean by 'fake ground'? I'm starting to wonder what kind of system you have there... do you have an earth terminal in your consumer unit? Does your 'real earth' go back to that earth terminal in the CU, and what is the 'fake ground'? I suppose I made the mistake of assuming it was similar to the Spanish system where it's a TN-S supply but they just don't bother supplying an earth to some sockets even though the sockets are designed to take plugs with an earth pin.

I don't suppose you're trying to say that in the unearthed sockets, they've connected the earth pin connection to the neutral?
 
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WarrenG

  • Thread Starter Thread Starter
  • #10
Why not disconnect the coaxial antenna as its causing you the problem to begin with and check it.

Not sure what type of anntenna it is but does it have any powered signal booster with it? And if so is this plugged into a grounded socket?

300mA leakage is alot and its coming from somewhere so there is more to this than meets the eye.

Or as its a RCBO are we looking at a direct short? Faulty powered anntenna? Check your own connections on the power supply you have changed are they correct?

With the anntenna disconnected from the PC and the PC unplugged, unplug all other equipment from sockets and switch the power back on. If the switch trips then you have an installation fault. If it doesn't trip try the following.

Plug in the PC without the anntenna (if the connections are correct) into a grounded socket (it should need an earth for leakage via the mains input filter) and see if you still have the problem.

If the switch goes again you need to have a closer look at your PC. If not start to plug the other equipment back into the sockets they came from. If the switch trips whilst plugging another piece of equipment in take a closer look at that.

If all the equipment plugs back in ok then there is a problem with the anntenna.

Let us know what your progress is.

Warren
 
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4x4 mark

  • Thread Starter Thread Starter
  • #11
before you try ripping everything to bits try a new rcbo in the board it might be that simple
 
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  • #12
-by fake ground i mean ground wire that doesnt go to the earth but to the "0" of the socket-
With the anntenna disconnected from the PC and the PC unplugged, unplug all other equipment from sockets and switch the power back on. If the switch trips then you have an installation fault. If it doesn't trip try the following.
Ok. So i disconnected every cable from the PC except the power cord and connected that to the grounded socket. The switch didnt trip. When i began plugging in the usb cables, it triped when i got to the printer cable. So i redid everything, without the printer and it didnt trip. Until i started turning on the lights inside the house, when it tripped yet again.

One time it tripped just when i plugged in the printer-non grounded socket-, without it being connected to the pc.

So, my guess is that Mark might have a point and the switch is to be blamed. ?! It doesnt trip at 300 mA, but at a lower value?
 
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Chappers

  • Thread Starter Thread Starter
  • #13
From everything you've said, it sounds like overall you have a lot of leakage to earth in your system. Turning on the lights was enough to push it over the limit and trip off. You need to start testing the circuits that are going back to that RCBO for earth leakage. It seems you have socket outlets and lighting circuits coming from that one RCBO?
 
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  • #14
Yes, everything goes through that RCBO switch...
 
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  • #16
It seems there is either some sort of problem with wire insulation (the house was made a long time ago and some parts of the electrical circuit havent been changed) or with the diferential switch.

And since i cannot fix either problem by myself, Ill call an electrician over to see whats going on...

Ill keep you posted!
 
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Chappers

  • Thread Starter Thread Starter
  • #17
Ill keep you posted!
Please do, it's always interesting to find out what the cause was of a problem. My money's on cable insulation deteriorated or faulty appliance/fitting somewhere leaking to earth.
 
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WarrenG

  • Thread Starter Thread Starter
  • #18
Please do, it's always interesting to find out what the cause was of a problem. My money's on cable insulation deteriorated or faulty appliance/fitting somewhere leaking to earth.
Yes Chappers it woukd be interesting to find out whats happening, a 300mA RCBO and a 'C' rating at that!

I am gonna go with 'switch on surges' for the kit plugged in. Mains filter capacitors charging up with a high leakage to earth.

If there is a 300mA RCBO fitted there must be an expect high leakage on the system in general. Add this to the kit surges and pop?????

Somethings a miss - extension keep us posted!
 
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  • #19
Well, the fake ground was the problem. It seems current exiting the appliances was going through both null and the fake ground. So when I plugged the computer to a real grounded socket, the fake ground got connected to the real ground and the current went from null to the earth.
 
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Chappers

  • Thread Starter Thread Starter
  • #20
When you say null, do you mean neutral? As in the neutral of the socket was connected to earth?
 
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  • Thread Starter Thread Starter
  • #21
Yes. Its an old house and this connection -neutral-ground- has been done in more than one socket. So, the electrician said he is going to remove that switch.

But Ive got a new question: what will happen when i plug in the antenna? Is there a chance that the current leaking throught it might destroy the tv?
 

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