Fitting glomex aerial - TV blew up!

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Ursula123

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Trying to fit 220v Uk TV on my boat to watch whilst plugged in to shore power in Spanish marina.
Fitted 2 prong Spanish unfused plug (TV is 2 core no earth) watched DVD no problem.
Next morning started to fit new Glomex disk aerial with 12v amp. ( as instructions)
Wired amp to multi-purpose cig lighter fitting I use for a inspection light into 12 v output, amp LED lit up -ok.
Wired coax from disk aerial to input socket of amp - ok
Fitted coax lead from output to TV as soon as it touched aerial socket at back of TV - Bang! big spark - TV is dead (presumably fuse)
Tested with volt meter - amp - 12v -ok
Tested output from amp to aerial socket on Tv - 220v!
Lugged TV back home, getting it fixed but what did I do wrong?
I am no sparky but thought this looked pretty straight forward.
Is it a polarity issue, the two prong unearthed plug can fit either way round in the socket.
Any help would be greatly appreciated.
 
Does sound as if the shield part of the TV's aerial socket is connected to the neutral side of its supply, which would be ok on a UK plug as neutral is tied to earth (either at your main fuse or at the nearest substation) but not good on the continent where live and neutral are interchangeable. But I thought TVs stopped being wired like that decades ago. If nothing else, they wouldn't be able to sell the same design in France as in UK, and since they're all made in China anyway, nobody wants that. Perhaps the TV has a fault?

Pete
 
Ursula123 said:
Tested output from amp to aerial socket on Tv - 220v!

Lugged TV back home, getting it fixed but what did I do wrong?
I am no sparky but thought this looked pretty straight forward.
Is it a polarity issue, the two prong unearthed plug can fit either way round in the socket.
Any help would be greatly appreciated.
Click to expand...

Are you saying that you were reading 220 volts on the coax coming from the antenna amplifier which you state was coupled to a 12 volt circuit ??
 
Bilgediver said:
Are you saying that you were reading 220 volts on the coax coming from the antenna amplifier which you state was coupled to a 12 volt circuit ??
Click to expand...

Not quite, I think he's saying there's a 220 volt difference between the TV's socket and the amplifier's cable that would plug into that socket. You can't have a voltage in isolation, it has be be between two points.

Pete
 
Maybe with a bit of luck the telly will be fried and the OP can get a 12v one....
These reversible mains plugs can be a nuisance in some instances, but I blame the telly - it shouldn't be a "hot chassis" version - unless it's a 405-line B&W..!
 
Billjratt said:
I blame the telly - it shouldn't be a "hot chassis" version - unless it's a 405-line B&W..!
Click to expand...

Agree, which is why I suspect it has an internal fault.

Presumably with 220v inside it it must be a CRT version. I haven't looked, but small LCDs must be peanuts now, and so much more practical on a boat. Time for replacement?

Pete
 
What I find confusing is the aerial/amp was plugged into to a 12v output. So how on earth did the amp input show 12v and the output show 220v. It doesn't make sense, there must be separate power and aerial/amp cables.
 
I don't think the outer of the coax should be neutral, it should either be ground or floating.
If it was neutral it would be prone to blowing RCD trips for one thing.


Some TV's have 5V on the aerial socket to power an amplified aerial. It's normally current limited and not damaged by shorting to the outer though.
 
KellysEye said:
What I find confusing is the aerial/amp was plugged into to a 12v output. So how on earth did the amp input show 12v and the output show 220v.
Click to expand...

It depends how you read this line:

Tested output from amp to aerial socket on Tv - 220v!
Click to expand...

Some people seem to be reading it as a test solely on the amplifier RF output, with "to aerial socket on TV" being added merely to clarify which connector he means. Presumably the actual measure would be the voltage between the centre pin and the screen - you can't measure the voltage of just one contact, the idea is meaningless.

If that's what is meant, then I share your puzzlement. However, I don't think that is what is meant.

I read it as a test of the voltage between the amplifier RF output and the TV aerial input, ie one multimeter probe on each. Not only does this explain where the 220 volts comes from (although not why), it's also the test that makes the most sense - having thrown unexpected sparks between two parts, the obvious thing to do is to see how much potential difference there is between them.

Of course, the OP's poor writing means it's not clear what actually happened, so I could be wrong, but that's my best guess.

Pete
 
prv said:
I read it as a test of the voltage between the amplifier RF output and the TV aerial input ...
Click to expand...
Ditto. I once got a very nasty belt from an antenna input socket, then thinking I must have imagined it, I did it again.

My question is, does "Fitted 2 prong Spanish unfused plug" mean that the OP fitted it, or it was fitted.
 
Last edited:
I think what has happened has been caused by the plug on the TV being incorrectly wired. The outer shield of the coax socket is usually grounded to the chassis of the TV which would be connected to the neutral side of the mains supply (I've had many surprises when I used to work at them and they were phased wrong). The 12v negative side of your amp is usually connected to the shield side of the coax socket. I presume on your boat the 12v negative is also connected to the engine block.So when you plugged in the coax plug to the back of the TV there is a direct path for the 230v via your engine block gearbox and prop directly to earth (water) hence the BANG.
 
Sounds like a telly fault. 220v AC should not matter which way round the plug goes as voltage is plus and minus around 0. Looks like the telly aerial outer was live. Unless it is something to do with not having a common ground so the chassis of the TV is not tied to the glomex and therefore there can be a significant potential difference between them.
 
Thanks guys for all your input.
Sorry if my post was confusing.
I tested the voltage between the end of the output lead from the 12v amplifier and the aerial input of the tv and it read 220v. When i initially tried to plug it in to the back of the Tv it really sparked.
Hope this helps
Thanks again
 
BERt T
You obviously know much more than me.
Didn't think it would be so complicated.
When I fitted the continental two pin plug neither connection inside was marked live or neautral, but then again without the earth prong you can plug it in either way in any case.
What did I do wrong?
 
Ursula123 said:
BERt T
You obviously know much more than me.
Didn't think it would be so complicated.
When I fitted the continental two pin plug neither connection inside was marked live or neautral, but then again without the earth prong you can plug it in either way in any case.
What did I do wrong?
Click to expand...

Ursula123
Have a look at this site: http://en.wikipedia.org/wiki/Earthing_system
Under normal circumstances you would not have this problem. It only occurred when you mixed the two systems 230v and 12v as I explained The only way round the problem is mark the plug and the socket that you normally use for the TV, so that each time you plug the TV in it is always connected the same way. After connecting up to your shore supply and before anything is plugged in always check with your meter set on 230v ac between the pin on the socket which you marked as the N and the negative of the 12v supply. If you are getting a reading of 200v to 230v then you need to reverse the connection to your shore supply. After doing so the 230v L should be on the correct pin of the socket and you should have no reading between the230v N pin and the 12v negative side. Hope this helps. PS make sure you have the blue wire in the plug connected to the pin you have marked as the N.
 
Ursula123 said:
BERt T
You obviously know much more than me.
Didn't think it would be so complicated.
When I fitted the continental two pin plug neither connection inside was marked live or neautral, but then again without the earth prong you can plug it in either way in any case.
What did I do wrong?
Click to expand...

Nothing. At least, nothing in the wiring. Europlugs are not polarised, so have no distinct live/neutral pins.

It's possible that your telly was not suitable for connection via Europlug though, and you should have used the proper polarised plug for the country you're in (not sure what that looks like for Spain). We're spoiled in this country by our excellent wiring system in which all appliances use the same plugs.

Pete
 
BERT T said:
Under normal circumstances you would not have this problem. It only occurred when you mixed the two systems 230v and 12v as I explained
Click to expand...

Absolute nonsense - please don't muddy the issue. The aerial socket was live before he ever went anywhere near it with any 12v kit.

Pete
 
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