Shocks from Aerial cable!!
Discussion
I brushed against the metal frame of the TV yesterday and noticed I got a shock. Assumed it was static and ignored it. Plugged a USB charger in another socket and got a slight tingle from a metal shield around the USB-C connection. I went back to the TV and, sure enough, got a shock from the metal surround.
I assumed a mains issue - earthing? but actually still got a shock with the TV unplugged. Turns out the shield of the aerial cable is sitting at around 70V when measured against the earth. I have a "splitter" and aerials/TV's in several rooms and by a process of elimination, it appears that 2 of the TV's in the house (both Samsung) are pushing about 46V to the shielded side of the aerial cable. I unplugged the aerial and measured from earth to the outside of the aerial socket, so it is originating from the TV. This is "adding" at the splitter end where the shields become "common" and resulting in the 70V I'm able to measure there. It's clearly leaking to the earth on my ring main and then any exposed metal on anything plugged in gives a shock when the TV's are plugged in...
Clearly this can't be normal - so what can I do about it? I find it hard to believe that 2 TV's have failed in exactly the same way with no other effects - they both function perfectly.
Any ideas? I had an electrician round, who verified my findings and left having confirmed there is nothing wrong with the house electrics and saying it has to be the TV's.
Anyone got any ideas, short of replacing 2 perfectly working TV's???
Appreciate any thoughts you might have.
I assumed a mains issue - earthing? but actually still got a shock with the TV unplugged. Turns out the shield of the aerial cable is sitting at around 70V when measured against the earth. I have a "splitter" and aerials/TV's in several rooms and by a process of elimination, it appears that 2 of the TV's in the house (both Samsung) are pushing about 46V to the shielded side of the aerial cable. I unplugged the aerial and measured from earth to the outside of the aerial socket, so it is originating from the TV. This is "adding" at the splitter end where the shields become "common" and resulting in the 70V I'm able to measure there. It's clearly leaking to the earth on my ring main and then any exposed metal on anything plugged in gives a shock when the TV's are plugged in...
Clearly this can't be normal - so what can I do about it? I find it hard to believe that 2 TV's have failed in exactly the same way with no other effects - they both function perfectly.
Any ideas? I had an electrician round, who verified my findings and left having confirmed there is nothing wrong with the house electrics and saying it has to be the TV's.
Anyone got any ideas, short of replacing 2 perfectly working TV's???
Appreciate any thoughts you might have.
None of the TV's or the Splitter have earthed connections - so the 70V is being distributed to the sockets and anything metallic connected to the earth on the same ring will give a shock.
I was worried that it didn't cause the trip in the consumer unit to go, but the electrician said it wouldn't and, having checked all our supply etc, said it's all fine.
I did wonder what would happen if I just connected the Aerial outer to earth, but thought I may be asking for trouble......
I was worried that it didn't cause the trip in the consumer unit to go, but the electrician said it wouldn't and, having checked all our supply etc, said it's all fine.
I did wonder what would happen if I just connected the Aerial outer to earth, but thought I may be asking for trouble......
bhippy said:
None of the TV's or the Splitter have earthed connections - so the 70V is being distributed to the sockets and anything metallic connected to the earth on the same ring will give a shock.
I was worried that it didn't cause the trip in the consumer unit to go, but the electrician said it wouldn't and, having checked all our supply etc, said it's all fine.
I did wonder what would happen if I just connected the Aerial outer to earth, but thought I may be asking for trouble......
I don't think it would cause problems but have only one TV connected just in case! As posted above it's probably just leakage through the mains filters on the TVs. If you're concerned use a pull down resistor (1k-10k ohm) instead of a piece of wire. I was worried that it didn't cause the trip in the consumer unit to go, but the electrician said it wouldn't and, having checked all our supply etc, said it's all fine.
I did wonder what would happen if I just connected the Aerial outer to earth, but thought I may be asking for trouble......
Either the TV has an earth wire or it is double insulated.
If it has earth, you'd expect the outer of the aerial coax socket to be low impedance to 'earth'.
If it's double insulated, it can float to any voltage, but there is no circuit involving 'earth' so it cannot put a significant current to earth via your finger as there's no return path.
Not only can it float to any AC voltage, it can also float to a DC voltage superimposed on that.
Sometimes with these things you will measure a voltage with a high impedance meter which is all but meaningless.
It can be a bit of capacitive coupling with no power behind it, not capable of driving a useful current.
Does the shock you felt continue or is it like a jolt of static?
It's possible the shock you feel is DC, the plastics of the system charging up. That could give a jolt you feel,
If you measure a voltage with a lower impedance meter like an old Avo, the 40V or whatever will have to drive a milliamp or some similar credible current.
So you could try grounding it via a 10k resistor or something, which would dissipate any high impedance, non-problem voltages.
There are also failure modes in these kinds of power supply which would explain what you have told us and could be lethal next time.
Maybe the 2 TVs got the same lightning strike or something?
It would help if you clarified double insulated or not (or even external psu box like my Sony) and confirm nothing connected.
If the 'splitter' is active, powered, or contains surge protection etc I am suspecting that.
Is the TV powered via surge protector or anything?
FFS Please be careful if you re-measure anything.
If it has earth, you'd expect the outer of the aerial coax socket to be low impedance to 'earth'.
If it's double insulated, it can float to any voltage, but there is no circuit involving 'earth' so it cannot put a significant current to earth via your finger as there's no return path.
Not only can it float to any AC voltage, it can also float to a DC voltage superimposed on that.
Sometimes with these things you will measure a voltage with a high impedance meter which is all but meaningless.
It can be a bit of capacitive coupling with no power behind it, not capable of driving a useful current.
Does the shock you felt continue or is it like a jolt of static?
It's possible the shock you feel is DC, the plastics of the system charging up. That could give a jolt you feel,
If you measure a voltage with a lower impedance meter like an old Avo, the 40V or whatever will have to drive a milliamp or some similar credible current.
So you could try grounding it via a 10k resistor or something, which would dissipate any high impedance, non-problem voltages.
There are also failure modes in these kinds of power supply which would explain what you have told us and could be lethal next time.
Maybe the 2 TVs got the same lightning strike or something?
It would help if you clarified double insulated or not (or even external psu box like my Sony) and confirm nothing connected.
If the 'splitter' is active, powered, or contains surge protection etc I am suspecting that.
Is the TV powered via surge protector or anything?
FFS Please be careful if you re-measure anything.
the issue of double insulated.
this means that the appliance is properly insulated in that you will not come into contact with any energised mains conductor.
There are four common protective measures as given in Regulation 410.3.3 of BS 7671:2018:
1. Automatic disconnection of supply (Section 411)
2. Double or reinforced insulation (Section 412)
3. Electrical separation (Section 413), and
4. Extra-low voltage provided by SELV or PELV (Section 414).
All of the above have a requirement for basic protection, which is the primary line of defence against electric shock and is typically achieved by insulation over the live parts, such as the insulation around a conductor, or a barrier inside an enclosure. The requirements for basic protection are described in Section 416.
Fault protection is the second line of defence, preventing (or limiting the effects of) an electric shock in the event that the basic insulation fails. In the case of automatic disconnection, a fault to the earthed exposed-conductive-parts results in operation of a circuit-breaker, fuse or RCD, thereby disconnecting the circuit and protecting the user and the installation.
Double or reinforced insulation is another method of protection against electric shock, consisting of an extra layer of supplementary insulation over the basic insulation, or a single layer of special reinforced insulation directly over the live parts. The latter provides basic and fault protection in one application and is commonly found in power tools for example. Class II products complying with the requirements for double or reinforced insulation in electrical safety standards will be marked with the double insulated symbol. It is possible to erect an entire electrical installation using only double or reinforced insulation as the protective measure, with all equipment – as well as the installation of wiring and accessories – complying with Section 412. Such an installation must be subject to effective measures (such as supervision) to ensure that no changes could be made that would impair the safety of the installation, as may happen if electrical equipment with exposed-conductive-parts is introduced.
Electrical separation as per Section 413 is commonly achieved by using a source which may be an electronic power supply or an electromagnetic transformer that provides at least simple separation. Fault protection is achieved by separating the secondary side from Earth and other circuits, thereby preventing the user from getting an electric shock to Earth. Finally, the extra-low voltages described in Section 414 again require basic protection between live conductors, but shock protection is achieved by the low voltages in the installation, which should be provided from a source meeting certain safety requirements.
Now the issue happens with the Ariel. on a double insulated TV there will be no earth in the TV so the chassis of the TV will be at the potential through the way the electronics in the TV work. Although no mains voltages through capacitance between the different parts within the TV you will find that there may be a voltage developed between the chassis and earth. Now this is where it gets interesting - if the ariel screen is isolated from earth and another TV is connected then you will see an increase in the screen voltage... This is due to the combination of the impedance from the two TV's causing the voltage to rise. current leak from one set through an impedance, another current passing through the impedance... bingo an increase in voltage.
its just one of those things. and you need to look at ways to try and ensure that voltage doesnt cause issues, you have already said you got a shock.
The shock you get is because the screen is at a voltage different to the general mass of the earth. To resolve I would be looking to tie down that screen to earth. then you will remove the difference between the screen and earth.
However if you earth the screen to the mains earth.... well that runs a risk as you export the earth to the antenna outside the building. Id be looking to tie it down to earth, but not the mains earth. that could be your answer. the likely hood of lightning aswell needs to be given consideration as you will see that earthing out your mast may make it an imprompto lightning rod.. however whether its earthed or not wont really make a difference with an ariel.. thease things sadly attract lighting.
this means that the appliance is properly insulated in that you will not come into contact with any energised mains conductor.
There are four common protective measures as given in Regulation 410.3.3 of BS 7671:2018:
1. Automatic disconnection of supply (Section 411)
2. Double or reinforced insulation (Section 412)
3. Electrical separation (Section 413), and
4. Extra-low voltage provided by SELV or PELV (Section 414).
All of the above have a requirement for basic protection, which is the primary line of defence against electric shock and is typically achieved by insulation over the live parts, such as the insulation around a conductor, or a barrier inside an enclosure. The requirements for basic protection are described in Section 416.
Fault protection is the second line of defence, preventing (or limiting the effects of) an electric shock in the event that the basic insulation fails. In the case of automatic disconnection, a fault to the earthed exposed-conductive-parts results in operation of a circuit-breaker, fuse or RCD, thereby disconnecting the circuit and protecting the user and the installation.
Double or reinforced insulation is another method of protection against electric shock, consisting of an extra layer of supplementary insulation over the basic insulation, or a single layer of special reinforced insulation directly over the live parts. The latter provides basic and fault protection in one application and is commonly found in power tools for example. Class II products complying with the requirements for double or reinforced insulation in electrical safety standards will be marked with the double insulated symbol. It is possible to erect an entire electrical installation using only double or reinforced insulation as the protective measure, with all equipment – as well as the installation of wiring and accessories – complying with Section 412. Such an installation must be subject to effective measures (such as supervision) to ensure that no changes could be made that would impair the safety of the installation, as may happen if electrical equipment with exposed-conductive-parts is introduced.
Electrical separation as per Section 413 is commonly achieved by using a source which may be an electronic power supply or an electromagnetic transformer that provides at least simple separation. Fault protection is achieved by separating the secondary side from Earth and other circuits, thereby preventing the user from getting an electric shock to Earth. Finally, the extra-low voltages described in Section 414 again require basic protection between live conductors, but shock protection is achieved by the low voltages in the installation, which should be provided from a source meeting certain safety requirements.
Now the issue happens with the Ariel. on a double insulated TV there will be no earth in the TV so the chassis of the TV will be at the potential through the way the electronics in the TV work. Although no mains voltages through capacitance between the different parts within the TV you will find that there may be a voltage developed between the chassis and earth. Now this is where it gets interesting - if the ariel screen is isolated from earth and another TV is connected then you will see an increase in the screen voltage... This is due to the combination of the impedance from the two TV's causing the voltage to rise. current leak from one set through an impedance, another current passing through the impedance... bingo an increase in voltage.
its just one of those things. and you need to look at ways to try and ensure that voltage doesnt cause issues, you have already said you got a shock.
The shock you get is because the screen is at a voltage different to the general mass of the earth. To resolve I would be looking to tie down that screen to earth. then you will remove the difference between the screen and earth.
However if you earth the screen to the mains earth.... well that runs a risk as you export the earth to the antenna outside the building. Id be looking to tie it down to earth, but not the mains earth. that could be your answer. the likely hood of lightning aswell needs to be given consideration as you will see that earthing out your mast may make it an imprompto lightning rod.. however whether its earthed or not wont really make a difference with an ariel.. thease things sadly attract lighting.
Edited by ruggedscotty on Friday 22 April 20:58
The TV's have just a live & Neutral in their plugs, so no earth wire, just a 2 pin connector into the back of the TV, not an external power supply.
The initial 70V was measured on the outside of the Aerial lead - the shield - by the electrician that came to check my mains. We pulled the aerial leads out of the TV's one by one to see where it might originate from and found that the 2 TV's were the source.
Pulling the Aerial cable from the TV it is possible to measure about 40V between the earth at the mains and the "shield" of the Aerial socket - which is seemingly doubling as when both are connected to the splitter, it goes to 70V.
So it's definitely originating in the TV's and, presumably because they have no earth in them, it's somehow getting back to the mains and anything plugged into that particular mains ring will give a shock if you touch the earth. If the TV's are unplugged, all is fine.
Electrician checked the mains fully and confirmed the problem isn't with the mains itself.
I was told if I just earth the shield of the Aerial cables, I risk making my Aerial into a lightning conductor and that it needs to float... Not sure how true that is...
I'm not aware of any power issues that may have caused a failure of these two TV's - however they are the same make and model....
The shock is small - you can feel it, but it doesn't hurt as such.
The initial 70V was measured on the outside of the Aerial lead - the shield - by the electrician that came to check my mains. We pulled the aerial leads out of the TV's one by one to see where it might originate from and found that the 2 TV's were the source.
Pulling the Aerial cable from the TV it is possible to measure about 40V between the earth at the mains and the "shield" of the Aerial socket - which is seemingly doubling as when both are connected to the splitter, it goes to 70V.
So it's definitely originating in the TV's and, presumably because they have no earth in them, it's somehow getting back to the mains and anything plugged into that particular mains ring will give a shock if you touch the earth. If the TV's are unplugged, all is fine.
Electrician checked the mains fully and confirmed the problem isn't with the mains itself.
I was told if I just earth the shield of the Aerial cables, I risk making my Aerial into a lightning conductor and that it needs to float... Not sure how true that is...
I'm not aware of any power issues that may have caused a failure of these two TV's - however they are the same make and model....
The shock is small - you can feel it, but it doesn't hurt as such.
ruggedscotty said:
Lots of info....
Many thanks for this and all the other responses - I think my post and this one were at the same time, so I hadn't seen this when I answered the previous poster.I really appreciate you taking the time to explain in such detail. How would you suggest I tie the Aerial to earth if not via the 'Mains Earth"? - and where would you tie it, at the splitter?
The TV set (and likely any attached Blu ray player or similar) will be using a switch mode power supply.
Most of these devices utilise the two pin 'figure of eight' plug which lacks any form of polarisation, and hence does not enforce live / neutral connections.
Most switch mode power supplies have a small value capacitor connected from the mains side to the 'ground' (chassis) of the TV set etc.
If the two pin plug just happens to be orientated incorrectly, this capacitor can end up connected to the live, resulting in a small leakage current into the 'ground' (chassis) of the device it's powering - and this will give you the shock as described.
The current is low enough to be harmless (because the capacitor is low value - typically around 1nF - 10nF or so) and won't even trip an RCD if the TV chassis is connected to mains earth.
I usually swap the (figure of eight) mains connector to switch polarity, and it often solves the problem.
Of course, if you have several devices like this, then a process of elimination is required to ascertain which device(s) are causing the issue.
Most of these devices utilise the two pin 'figure of eight' plug which lacks any form of polarisation, and hence does not enforce live / neutral connections.
Most switch mode power supplies have a small value capacitor connected from the mains side to the 'ground' (chassis) of the TV set etc.
If the two pin plug just happens to be orientated incorrectly, this capacitor can end up connected to the live, resulting in a small leakage current into the 'ground' (chassis) of the device it's powering - and this will give you the shock as described.
The current is low enough to be harmless (because the capacitor is low value - typically around 1nF - 10nF or so) and won't even trip an RCD if the TV chassis is connected to mains earth.
I usually swap the (figure of eight) mains connector to switch polarity, and it often solves the problem.
Of course, if you have several devices like this, then a process of elimination is required to ascertain which device(s) are causing the issue.
bhippy said:
ruggedscotty said:
Lots of info....
Many thanks for this and all the other responses - I think my post and this one were at the same time, so I hadn't seen this when I answered the previous poster.I really appreciate you taking the time to explain in such detail. How would you suggest I tie the Aerial to earth if not via the 'Mains Earth"? - and where would you tie it, at the splitter?
it would be a case of taking that screen through some form of connection down to earth. Earth being a local earth rod not linked to your mains earth. that would need to be kept separate.
there are many trains of thought on this.
leave it un earthed and deal with the zap.
earth it to the mains earth - however that is introducing a risk. although small its still a risk. Also due to the Uk mains being generally PME there is a slight risk of there being a potential between the voltage between the real earth and the bonded metal work.
use your own earth rod and run a 6mm earth cable from the rod to the aerial and ground the braid. This however runs the risk again small of having a true earth inside the building and the mains earth voltage being different.
So you see how it develops.
The americans have a specific way of earthing a TV antenna. and they use the mains earth to ground the screen and then there is a drain device to drain any excessive charge from the aerial lead.
If it were me, I would take an earth from the main earth terminal and use that, and bear in mind that your exporting an earth. to the aerial. If thats the case then i would be ensuring that the aerial is out of the way. and that within the house that lead screen is grounded.
its making a decision on whats best. I may be that you decide to leave it and just be cautious around it. disconnect the tv before working with it etc.
Fact is, you don't get jolts from properly made, safe double insulated household goods in good working order.
You shouldn't be considering elaborate nonsense about earthing your TV aerial.
You should be taking the Samsung WEEE back to the shop.
From what you have said, it is defective.
It seems like a fault that is unlikely to have always been there, and is likely to get worse, with risk of electrocution or fire.
Power supply fault in something that's always plugged in, often unattended, not in my house, thanks.
You shouldn't be considering elaborate nonsense about earthing your TV aerial.
You should be taking the Samsung WEEE back to the shop.
From what you have said, it is defective.
It seems like a fault that is unlikely to have always been there, and is likely to get worse, with risk of electrocution or fire.
Power supply fault in something that's always plugged in, often unattended, not in my house, thanks.
OutInTheShed said:
Fact is, you don't get jolts from properly made, safe double insulated household goods in good working order.
You shouldn't be considering elaborate nonsense about earthing your TV aerial.
You should be taking the Samsung WEEE back to the shop.
From what you have said, it is defective.
It seems like a fault that is unlikely to have always been there, and is likely to get worse, with risk of electrocution or fire.
Power supply fault in something that's always plugged in, often unattended, not in my house, thanks.
oh thats good to know.....You shouldn't be considering elaborate nonsense about earthing your TV aerial.
You should be taking the Samsung WEEE back to the shop.
From what you have said, it is defective.
It seems like a fault that is unlikely to have always been there, and is likely to get worse, with risk of electrocution or fire.
Power supply fault in something that's always plugged in, often unattended, not in my house, thanks.
also google - it is normal these days to have volts on the braid. many have given valid reasons on why this happens.
the thing to consider is the braid is metal it connects to the tv, as its earth free there are all sorts of stray capacitance and induced voltages that can end up on the ariel. double insulated it may well be but it aint free of voltages. its just well insulated from the mains.
ruggedscotty said:
oh thats good to know.....
also google - it is normal these days to have volts on the braid. many have given valid reasons on why this happens.
the thing to consider is the braid is metal it connects to the tv, as its earth free there are all sorts of stray capacitance and induced voltages that can end up on the ariel. double insulated it may well be but it aint free of voltages. its just well insulated from the mains.
I explained in my post above why this happens. I believe somebody else also mentioned about line filters which can also cause this as well.also google - it is normal these days to have volts on the braid. many have given valid reasons on why this happens.
the thing to consider is the braid is metal it connects to the tv, as its earth free there are all sorts of stray capacitance and induced voltages that can end up on the ariel. double insulated it may well be but it aint free of voltages. its just well insulated from the mains.
OutInTheShed said:
TonyRPH said:
I explained in my post above why this happens. I believe somebody else also mentioned about line filters which can also cause this as well.
You did.I think you are wrong.
The OP could get it PAT'd.
The PAT will do a leakage and insulation test, class II item of kit. it will pass....
plug it back in and he will still have the voltage on the screen of the antenna cable.
How can that be if its passed the PAT test, is it safe or not...
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