Leakage current from TV
Rob Graham
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
> 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.
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.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org
Grouch
"Rob Graham" <robkg...@lineone.net> wrote in message
news:700de225.04022...@posting.google.com...
Sorry about that, is your TV still working. :o)
Grouch
---
Confucious say" Woman who cooks carrots and peas in same pot is
unsanitary"
http://www.zonelabs.com
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.596 / Virus Database: 379 - Release Date: 26/02/2004
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.
--
Grunff
Harry Bloomfield
> 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.
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
mike ring
news:mesnews.e54b7d42....@tiscali.co.uk:
> On 28/02/2004 Grunff a wrote :
>> 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.
>
> 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.
>
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
mike ring <mike...@MICHAELbtinternet.com> wrote:
> 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.
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.
> 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
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.
--
*Growing old is inevitable, growing up is optional
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Andrew Gabriel
Grunff <gru...@ixxa.com> writes:
> Rob Graham wrote:
>>
>> 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.
>
> 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.
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
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?
--
Andrew Gabriel
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
Tony Williams
Rob Graham <robkg...@lineone.net> wrote:
> 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.
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.
--
Tony Williams.
Dave Plowman
Andrew Gabriel <and...@cucumber.demon.co.uk> wrote:
> 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?
Don't think I've *ever* seen a TV with an earth.
--
*Parenthetical remarks (however relevant) are (usually) unnecessary *
tony sayer
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....
--
Tony Sayer
Scott Mills
"N. Thornton" <big...@meeow.co.uk> wrote in message
news:a7076635.04022...@posting.google.com...
>
> Question: why arent aerial systems normally earthed?
I don't think they would work earthed - although I have only given it a very
quick thought...
>
> Regards, NT
Lurch
wrote:
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
> 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.
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!
--
Scott
Where are we going and why am I in this handbasket?
Rob Graham
> Rob Graham wrote:
>
> > 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.
>
> 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!
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
Terry
Just a thought. Do you get that spark/voltage when the TV set is on or when
off?
It occurs to me that maybe the on/off witch might be in the neutral lead of
the AC mains input?
So even when switched off could the set be 'sort of' floating at 230 volts
above neutral and earth????
Not familiar what the UK standard's require the on/off switches of
appliances such as TVs to do.
Here, Canada, our smaller appliances generally operate at 115 volts. And the
on/off switch is a single pole that disconnects the 'live' 115 volt above
neutral lead.
Tony Williams
Rob Graham <robkg...@lineone.net> wrote:
[big snip]
> .....................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.
Trading Standards may be interested, or may be able to
suggest the official body to complain to. They may
also suggest of course that your first port of call is
to return the set to the place you bought it from.
--
Tony Williams.
tony sayer
<to...@ledelec.demon.co.uk> writes
Just to confirm your measuring how many ma from the aerial socket to
where exactly?.
'Cos I bet every TV in this house is doing the same.....
--
Tony Sayer
not available
The internal power supply of a TV is such that the "earth" - ie
external metal parts - sit at half the supply votage. This means that
you will get the same effect no matter which way around the mains are
connected. This is a high impedance path so the current is minute. In
some circuits it is possible to see an actual resistor that
constitutes the bulk of the impedance.
The leakage resistance between the mains - line and neutral joined
together for the test - is in the range of 2 Meg ohm upwards. This is
well within the current (no pun) PAT testing guidlines for class 2
equipment. Typically we have between 2.2 Megohm (Philips/Grundig) and
8.2 Meg ohm (JVC) on the TVs we use in our installations.
This leakage path is to allow any build up of static to leak away.
In the "olden" days of valve circuits the "chassis earth" was
connected to the mains neutral and would be at 240v if the plug was
connected the wrong way round!
Hope this helps.
anon
On 7 Mar 2004 12:50:40 -0800, robkg...@lineone.net (Rob Graham)
wrote:
stefe...@hp.com
>
> The internal power supply of a TV is such that the "earth" - ie
> external metal parts - sit at half the supply votage. This means that
> you will get the same effect no matter which way around the mains are
> connected. This is a high impedance path so the current is minute.
>
leakage resistance of 2.2 megohm and up. For ease of rithmetic, call it
2.4meg; with a 120V half-supply-voltage, we'd expect a current of
120/(2.4*1,000,000) = 100 / (2,000,000) = 50 / 1,000,000. That's just
50 of your planet-Earth's microamps.
The original poster reports a measured current of some 3.5mA - about
3 orders of magnitude (1000 times) more than the resistive path you
mention would pass; reports that the voltage is 240V rather than 120V;
and reports the voltage Goes Away when L&N feeds are reversed. From where
I'm sitting it's at least suggestive of a fault (whether in design or
in the particular bit of kit isn't clear).
Stefek
tony sayer
Capactive coupling somewhere?...
--
Tony Sayer
stefe...@hp.com
>
> Capactive coupling somewhere?...
Presumably so, but it's no small-signal cap to let this much current flow.
We see 4mA at 240V, so the impedance is 240/(4/1000) = 240,000/4 = 60kOhm.
Capacitive impedance is 1/(2*pi*f*c), innit? So we have
60,000 = 1/(6 * 50 * c) [using the Indiana convention for value of pi :-]
60,000 = 1/300*c, so 300*c = 1/60,000,
so c = 1/(300 * 60,000) = 1/ 18,000,000,
call it 1/20,000,000 = 0.05uF or 50nF.
Oh, is that all? I stand corrected - a 0.05uF cap is a perfectly plausible
value to see in a suppression cap. (Walks across room: yes, I see some
mains-rated suppression caps in the Spares Box at 10nF, which reversing
the above calc would pass on-the-order-of 1mA at 240V).
Note, though, that 50nF is *much* higher than 'accidental' capacitive
coupling (i.e. wires running close together) would give over TV-set-internal
wiring distances (cable capacitance for intimately-close conductors in
e.g. coax or twisted-pair is of the order of tens of pFs per metre), so
this looks like a 'real' capacitor deliberately providing a path from
live to the aerial socket: and of too high a value to give unproblematically
negligible current....
Stefek
Tony Williams
tony sayer <to...@bancom.co.uk> wrote:
> Tony Williams writes
> > Trading Standards may be interested, or may be able to
> > suggest the official body to complain to. They may
> > also suggest of course that your first port of call is
> > to return the set to the place you bought it from.
> >
> Just to confirm your measuring how many ma from the aerial socket
> to where exactly?.
> 'Cos I bet every TV in this house is doing the same.....
I still think that there is a good chance that this tv has
L-N swapped, now more or less confirmed by the OP when he
reported that the problem of an apparently live aerial
socket disappeared when he ran with (re?)reversed L-N.
It suggests that there is a 0.05u capacitor (more likely
a 0.047u and parallel leakage resistor) connected between
the outer of the aerial socket and the incoming Neutral.
The purpose of this capacitor is to keep the main aerial
assembly at a safe low voltage.
Trouble is, if L-N get swapped then the inboard end of
that cap will be at 240V.
It really does sound like the OP ought to take the back
off and do a visual inspection of the incoming mains
connections. The mains lead will probably terminate in
a pc-mounted plug and socket, (of the Molex-type), with
crimped leads into the free socket, plugging into a pcb
male header plug. These are normally polarised to prevent
wrong-way-round insertion, but sometimes can be forced
in backwards. So that is the first thing to look at,
a plug and socket that looks jammed-in and 'wrong'.
If that looks ok, then it could be that the incoming
L-N wires are inserted wrongly in the free socket.
But these wires can't be swapped willy-nilly, the circuit
would have to be traced, find that 0.05-ish uF cap that
should be connected to the can of the tuner, and trace
it back to the incoming mains, to identify which pin
should be the Neutral.
--
Tony Williams.
Andy Wade
news:c2j1jh$79a$1...@murdoch.hpl.hp.com...
> In uk.d-i-y, tony sayer <to...@bancom.co.uk> wrote:
>> Capactive coupling somewhere?...
> Presumably so, but it's no small-signal cap to let this much current
> flow. We see 4mA at 240V, so the impedance is 240/(4/1000) =
> 240,000/4 = 60kOhm.
> Capacitive impedance is 1/(2*pi*f*c), innit? So we have
> 60,000 = 1/(6 * 50 * c)
You are making the assumption that the leakage is all at 50 Hz, which is
almost certainly not the case. Much of it will be at line-scan rate (15,625
Hz in Europe) and/or higher SMPS switching frequencies, and, moreover, is
likely to be distinctly non-sinusoidal in waveform.
The max. leakage from a TV set (or any other home electronics equipment for
that matter) is defined in the safety standard EN 60065 (formerly BS 415).
Leakage (actually called 'touch current') is assessed by measuring voltages
at two points in an R-C shaping network connected between the antenna socket
(or other accessible terminal) and earth. To simplify a bit, the network
essentially consists of a 500 ohm shunt resistor, followed by a lowpass R-C
filter with 220 us time constant (~700 Hz corner frequency). The
requirements are these:
- at DC: max. drop across the 500 ohms = 1 V (2 mA leakage)
- for AC: max. drop across 500 ohms = 35 V peak AND max. voltage
after the filter network = 0.35 V peak.
The effect of the latter is to limit low-frequency leakage to 0.7 mA peak
(0.5 mA RMS, if it's sinusoidal) but allows higher leakage at higher
frequencies, asymptoting to 70 mA peak for f>100 kHz or so.
A leakage figure measured with a multimeter is pretty meaningless if you
don't have knowledge of the frequency spectrum and waveform.
> Oh, is that all? I stand corrected - a 0.05uF cap is a perfectly
> plausible value to see in a suppression cap. (Walks across room:
> yes, I see some mains-rated suppression caps in the Spares Box at
> 10nF, which reversing the above calc would pass on-the-order-of 1mA
> at 240V).
It would be unusual to find a class Y (mains to earth) capacitor more than
4n7 in consumer electronics. The higher values will by class X types, for
use across the mains.
Somebody else asked why (TV) aerial systems aren't earthed. In some cases
they are: any distribution system feeding more than one dwelling unit should
be earth bonded. The standard is EN 50083-1 and the Ofcom class licence for
such systems makes this a legal requirement. This has superseded the former
practice of using isolated outlet plates, which are a disaster EMC-wise.
Also, in some cases, aerial masts may be bonded to a lightning protection
system, which in turn will be bonded to mains earth. Earth bonding single
domestic aerial systems is still fairly unusual in the UK, but is standard
practice in Germany, AIUI. Beware of hi-fi hum-loop problems via your FM
tuner...
--
Andy
The Natural Philosopher
>
> Capactive coupling somewhere?...
>
Certainly hat is one thing that DOES happen
We had some eejit witha laptop plug it via a serial cable into anoher PC
and there was a small flash, and it destroyed teh serial card.
I stuck a meter on it, and discivered the laptop earth sitting at 115v AC.
Basically there was a filter in the power supply to connect live and neutral
via two small caps to earth, but only a two wire mains lead...
Lots of sets are built like that, and the earth needs earthing.
This does not seem to be what is going on here because the live/neutral
swap fixed it.
The Natural Philosopher
I thik you are spot on here.
stefe...@hp.com
>
> You are making the assumption that the leakage is all at 50 Hz, which is
> almost certainly not the case. Much of it will be at line-scan rate (15,625
> Hz in Europe) and/or higher SMPS switching frequencies, and, moreover, is
> likely to be distinctly non-sinusoidal in waveform.
>
- every difference in the world between a practicing electronics engineer
in touch with modern mains-powering practice such as yourself, and a
software geek dredging up teenage (and that's 30+ years back, folks)
basic-electronics principles!
Ta muchly - Stefek
Dave Plowman
Tony Williams <to...@ledelec.demon.co.uk> wrote:
> It suggests that there is a 0.05u capacitor (more likely
> a 0.047u and parallel leakage resistor) connected between
> the outer of the aerial socket and the incoming Neutral.
> The purpose of this capacitor is to keep the main aerial
> assembly at a safe low voltage.
All that suggests a set made for the UK only - as pretty well everywhere
else doesn't use polarized mains plugs for TVs, etc.
--
*Reality is a crutch for people who can't handle drugs.
Rob Graham
Come on guys, this thing is clearly wired back to front (A*** over T**
to be colloquial) and it's pretty poor practice that the manufacturer
doesn't have a test to protect the end-user from this hazard. That's
my grump.
There is sufficient 'power' at the aerial sleeve to get a shock - OK a
tingle, but that's the same thing, and to some people that could be a
hazard; to most of us who dabble with electricity, shocks are part of
the game. There's sufficent 'power' that in the gloomy hole behind my
TV I can see spark when the aerial is connected to the distribution
system. OK that may be a capacitative load but it's charging that
load up to the voltage on it. The 'fault' is consistent whatever
mains socket I plug the TV into. It is present whether the TV is on
or not so there's no way it can be related to switching power
supplies, etc,. The voltage disappears back to zero when the mains
socket is switched off which is reasonable. And there is no voltage
at the user accessable point when I run the TV on 'reversed' L and N.
Ergo it's the equipment.
The Trading Standards guy is coming to see it on Friday.
Rob
roger
>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.
>
is 0.25mA.
I looked it up after getting 0.2mA from a Maxtor external HDD.
This gives you a tingle but not a real shock.
What did the TS guy say?
--
roger
Delete x's to email
Tony Williams
Rob Graham <robkg...@lineone.net> wrote:
> There is sufficient 'power' at the aerial sleeve to get a shock -
> OK a tingle, but that's the same thing, and to some people that
> could be a hazard;
A typical hazard could be you, standing on the top
of an aluminium ladder, one hand on the ladder for
safety, the other reaching up to adjust the aerial.
The current probably wouldn't hurt you, but the
fall could.
The other (possible) problem is that the capacitor is
not rated to have a permanent 240Vrms across it, but
could have if the incoming coax were to be earthed.
That could make the capacitor a fire hazard.
> The Trading Standards guy is coming to see it on Friday.
Good. Hope you find a clear reason for the 'live'
connector. Take plenty of photographs.
--
Tony Williams.
tony sayer
<to...@ledelec.demon.co.uk> writes
>In article <700de225.04031...@posting.google.com>,
> Rob Graham <robkg...@lineone.net> wrote:
>
>> There is sufficient 'power' at the aerial sleeve to get a shock -
>> OK a tingle, but that's the same thing, and to some people that
>> could be a hazard;
>
> A typical hazard could be you, standing on the top
> of an aluminium ladder, one hand on the ladder for
> safety, the other reaching up to adjust the aerial.
> The current probably wouldn't hurt you, but the
> fall could.
>
Bin there, felt that:-(
> The other (possible) problem is that the capacitor is
> not rated to have a permanent 240Vrms across it, but
> could have if the incoming coax were to be earthed.
> That could make the capacitor a fire hazard.
>
>> The Trading Standards guy is coming to see it on Friday.
>
> Good. Hope you find a clear reason for the 'live'
> connector. Take plenty of photographs.
>
Trust the trading standards guy knows all about this, or at least knows
a man that does!....
--
Tony Sayer
Rob Graham
Well the 'TS' man came in a week ago and did at least have the
courtesy to phone me yesterday to tell me that problem had been passed
onto the TS man that deals with Panasonic and another one who deals
with the supplier. Otherwise he didn't really have the technical
knowledge to take on board the measurements I was showing him, but did
seem to know some of the buzz words. He at least was picking up on
the concern that the fault might be endemic to other similar models.
It's not known yet whether the plug is wired wrong or the cable into
the set; what is suprising is that Panasonic don't do the simple test
of checking the aerial sleeve to make sure that mains is wired
correctly - kind of basic really.
Rob
not available
Andy Luckman (AJL Electronics)
<URL:mailto:an...@nowhere.com> wrote:
> Any answer from the Trading Standards yet?
About what?
--
AJL Electronics (G6FGO) Ltd : Satellite and TV aerial systems
http://www.classicmicrocars.co.uk : http://www.ajlelectronics.co.uk
** Would you like to learn to post effectively? **
** http://www.allmyfaqs.com/faq.pl?How_to_post **
Lurch
Electronics)" <m...@privacy.net> strung together this:
>In article <u1fj60lde353d7fsr...@4ax.com>, not available
><URL:mailto:an...@nowhere.com> wrote:
>
>> Any answer from the Trading Standards yet?
>
>About what?
>
Excessive current leakage from a TV, oddly enough. There's a
substantial thread on it somewhere, google's what you want.
--
SJW
A.C.S. Ltd.
Andy Luckman (AJL Electronics)
<URL:mailto:bill....@microsoft.com> wrote:
> >About what?
> Excessive current leakage from a TV, oddly enough. There's a
> substantial thread on it somewhere, google's what you want.
Ah, it was actually a loaded question because the context was upside down
and untrimmed etc. I was hoping he might take the hint and read the posting
link but I was obviously being too subtle (unlike me!) :-)