Leakage current from TV

[Rob Graham]

I recently bought a new Panasonic TV. The house TV networking system needed to be rebuilt and while doing so I kept on getting a tingle off one of the coax connectors. Didn't think to much about it until I noticed a small spark when connecting one of the coax connectors. It was time to investigate.

It turned out that with respect to the piping to the nearby stove, the leads to all the remote TV's in the house were at nominally zero volts AC, but that the voltage on the sleeve of aerial coax of the new TV was at 240 Vac. I then measured 4.2mA current to ground. If I switch off the mains to this TV, the voltage disappears.

Can anyone comment please.

Rob

[Harry Bloomfield]

Rob Graham wrote on Saturday (28/02/2004) :

Some small amount of leakage is perfectly normal, though I cannot specify what the actual limit is. Try uplugging the antenna leads from other TV's and measuring their leakage to ground when turned on, just as you have done with the new TV.

[Grouch]

switch

Sorry about that, is your TV still working. :o)

Grouch

[Grunff]

It wouldn't suprise me that the aerial socket floats at a good few volts, but the fact that it's at 240 does surpise me a bit. An the fact that it can source 4mA is even more worrying.

[Harry Bloomfield]

Remember, it is not 4mA at 240v, it is 4mA delivered to an absolute short to ground. The antenna sockets are isolated from the rest of the TV chassis by capacitors which allow the UHF TV signal through, but attempt to block lower frequencies and DC.

[Grouch]

switch

Take a look here, it's a Hospital TV mind but the question is the same.

[mike ring]

Harry Bloomfield wrote in news: [e-mail]:

I think that the sort of capacitance needed to provide a decent path for

700 odd megahertz should let a LOT less than 4.2 mil at 50 Hz.

It's a bit late for me to attempt the sums, can't talk puffs without limbering up, I've been out of it too long, but I'd be very suspicious of that set

mike r

[Dave Plowman]

There's a good chance the screen of the Belling Lee plug is connected to chassis, and it's small resistors from mains to this causing the problem.

I've had one set that caused an earth loop on the audio when the aerial was plugged into the DA. Isolating the socket screen with a small R/C network cured it with no apparent problems signal wise, but I'm in a very strong signal area.

[Andrew Gabriel]

I don't have the relevant EN, but I believe the limit is 0.75mA. If you are confident of your 4mA measurement, take it back as faulty, and more seriously, electrically unsafe.

[Andrew Gabriel]

Actually, the 0.75mA is max leakage for a Class I (earthed) appliance, and that would be leakage down the earth conductor. You don't say if this is a Class I or Class II (double insulated) appliance, but in neither case should 4mA be available. What is the open circuit voltage you measure between the appliance and ground?

[Tony Williams]

4mA is about the current that a 0.05uF would pass when it has 240V across it.... 0.05uF would be a plausible value between the low-side of the tuner and the rest of the circuitry.

It does raise the possibility of a TV set (or 13A socket?) with reversed L-N wiring.

[N. Thornton]

Hi.

4.2mA is much too high. If the ae socket is not PCB mounted then 2 mains rated caps (of the live to earth rated type) on the inside of the TV can make the ae socket safe again - but if there are any other external chassis connections like scart, headphone, etc youve got a problem.

Mains voltage on the socket OTOH is not so significant by itself: most TVs will have a little leakage, although not 4.2mA.

Question: why arent aerial systems normally earthed?

Regards, NT

[Dave Plowman]

Don't think I've *ever* seen a TV with an earth.

[tony sayer]

In article , Rob Graham writes

Quite normal. Its the way TV power systems work. Better these days once the used to have one side of the chassis directly connected to the mains so the whole of the metal inside could have been live!. Hence what an important part the aerial isolator panel is/was.

Nowadays some sort of switch mode arrangement is often used but with the same sort of leakage found from time to time....

[Scott Mills]

I don't think they would work earthed - although I have only given it a very quick thought...

[Lurch]

They do work earthed, I have fitted commercial distribution systems and all outlets have been earthed at a central location. It's the way it's done and it all works perfectly. ..

SJW A.C.S. Ltd.

[Scott M]

Had an oldish Panasonic that did exactly the same thing. Never seemed to do any harm, apart from making you jump if you were playing with the aerial leads while it was on!

[Rob Graham]

Well I had another go at this this week-end. I did very much contribute to the suggestion that the mains socket could be the wrong way round - it is spur and I did the wiring and lets be honest, however careful one is, errors do occur. Inspection, and measurement, showed that my wiring was OK and that the line was the line and not the neutral.

So -- tried the TV on another socket - same high voltage on the aerial sleeve. Tried it on the same socket as one of the other TV's in the house that have zero volts at that point and the same high voltage. Reasonable to assume therefore that it is the TV. It is now running on an extensiion lead with the line and neutral swopped over and the aerial is at zero.

Now the current flowing out of the aerial previously is at a dangerous level - I can't remember the BS number that applies but 3.5 mA is the recognised standard for earth leakage that we use at work, and this isn't actually earth leakage. This TV is an potential danger and it would seem that Panasonic do not test to ensure that the mains lead is correctly wired. They won't change if I point it out to them but they will if I get the correct authority involved - can someone tell me the right place to go to please.

Rob

[Andy Luckman (AJL Electronics)]

About what?

[Lurch]

On Thu, 1 Apr 2004 15:11:59 +0100, in uk.d-i-y "Andy Luckman (AJL Electronics)" strung together this:

Excessive current leakage from a TV, oddly enough. There's a substantial thread on it somewhere, google's what you want.