Earthing an aerial socket

[dave2506]

Hope you can help as I'd like some clarification before I go ahead with the following.

I'm installing a new aerial socket in our bedroom that will be connected to the aerial and sky box downstairs via a small 2 channel ampifier/splitter in the loft. I'm fitting the socket using a flush mounted metal back box and then chasing out the wall up to the ceiling to hold some oval conduit, inside which the coax cable will run. The faceplate of the socket will be metal to match the other sockets in the room.

I need some advice as to whether the faceplate and back box (both metal) should be earthed in any way. My friend has told me that it doesn't need it but then why would the faceplate have an earth terminal? If indeed it does need earthing what is the best way to do this as it won't run near any of the main power/lighting circuits in the house.

 

[ericmark]

There are conflicting reports on this.
Some consider to earth an aerial makes it more likely to get a lighting strike and warn against earthing.
Others point out the possibility of during atmospheric storms that the aerial can become charged and one should earth so you will not get a shock.
To me the idea of a direct strike on the aerial is of far more concern to live sockets so I used an insulated socket and no earth.
The regulations say there are not enough atmospheric storms in the UK to worry about it but I have seen the results of a lighting strike on a G5RV aerial which it turned into copper bits across the lawn a little bigger than a TV aerial I know but had a coax feeder instead of 300 ohm ribbon been used and in the wall rather than in free air the results would be much worse.
I am told a spark gap and leak resistors like used in master telephone socket is best option and for a G5RV maybe I would but for a 70cm yargi beam think that is a little OTT and I just unplug in thunder storms.
Satellite dish which is a lot lower and on wall I don't bother unpluging.
Of course loft aerials are OK too. I am told you should avoid fitting an aerial on sharp edges like gable ends and where there is any conduction to earth like soot coated chimney which seems to be against the normal practice. So you will have to make up your own mind as to which to do.
Eric

 

[dave2506]

Hi Eric

Thanks for your reply - all sounds like good advice! My only query is that shouldn't the external roof aerial be earthed anyway - therefore providing a safe passage to ground should it be struck by lightning?

In all honesty I hadn't thought about the consequence to the socket should the aerial be hit by lightning. Although the wiring configuration may eliminate this risk anyway (aerial --> sky box --> amp/splitter --> secondary aerial socket).

 

[holmslaw]

..

 

[BS3036]

To an extent, a 'lightning conductor' is actually a 'lightning preventer'. During a storm, the potential difference between the ground and the air above causes a spray of electrons to be emitted by the sharp point at the top. This spray actually has the effect of de-ionising the surrounding air, making it much less likely that the discharge will choose this path to ground.

However if the discharge does in fact choose this path, then it is likely that it will then choose the conductor, rather than the nearby building parts.

 

[ericmark]

We don't live in the Congo so no so important here but as to earthing it would need at least a 50mm earth cable likely a lot bigger to handle lighting strikes and I would say don't earth.
But this subject has been raised before and its a case of light blue touch paper and retire to safe distance as people have some very different ideas and it is unusual to get two people both saying don't earth as only replies.
As to loft boxes etc. They don't tell you what's inside so you can only guess. My house has band pass filters all around the place which will likely isolate as well but in the past I use to transmit at around 30 watts on 2 meter band so a little unusual but my father-in-law had a problem not direct strike but took Video and TV out so if video did not protect I would not think any other pre-amp would protect either.
Eric
PS BS3036 needs to get books out again I think! I said this was blue touch paper job!!!

 

[dave2506]

Thank you to everyone who replied so quickly. By the look of it I'm safe to install the new aerial point without earthing the socket (much to my relief!). Just need to chase out the wall and get it all plumbed it before I can start enjoying my sky in bed (that is once I've bought another TV!).

 

[sparkyspike]

Just one thing - if you are using a metal plate tv point, it shouldn't be adjacent to a metal plate power outlet, unless there is a good gap between them.

 

[dcwuk]

Just one thing - if you are using a metal plate tv point, it shouldn't be adjacent to a metal plate power outlet, unless there is a good gap between them.[/quote

wtf

 

[dcwuk]

If you take a look at a metal aerial socket you will see that the actual aerial connection and socket is insulated from the metal face plate.
the metal face plate will have an earth terminal which should be used in my opinion.
Further to this regardless as to whether or not the aerial socket is metal or not the metal back box should be earthed.
dcw

 

[electronicsuk]

This is an interesting one and has brought about some debate, but can those who work on the basis that a metal backbox for an aerial socket should be earthed please explain why this is so?

It has always been my opinion that the only point of earthing in a TV distribution system should be at the head end, with all incoming/outgoing cables to/from the distribution amp bonded back to the CU my means of a 4mmsq conductor. Anything in addition to this is simply adding extra earth paths and the possibility for ground loops should the faceplate/screws of any outlets be electrically linked to the sockets themselves, which will only be more problematic in the future.

Next people will be saying that the earth terminal in a plastic backbox must always be connected, it makes just about as much sense...

 

[flameport]

electronicsuk is correct. Earth bonds are fitted in the headend only, this is to prevent faults in one property spreading to the TV sockets in others (used to only be an issue in blocks of flats, but could occur in single properties now that a TV can be fitted in every room).

As for lightning - don't bother unplugging the aerial when there is a storm. If your house is hit by lightning, most of it will be destroyed and whats left will be on fire. The last thing you will be concerned about is if your TV is still working. Even worse - by touching the end of the aerial lead, you are providing a path directly to earth for the lightning to follow.