drgeoff
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 23, 2020 10:18 pm

klricks wrote:
Tue Jun 23, 2020 8:42 pm
I hope it is OK if I post something on topic?.......

If I touch a grounded object with one hand (Back panel of the PC) and lightly touch or drag my finger across the port shields of the RPi with the other hand, I do get a sensation. It's more of a vibration sensation rather than a shock. I have felt this same thing in many other electronics and am not bothered by it.
That's the classic case of the small value capacitor between input and output side of a switch mode mains AC to DC PSU as exemplified by the official RPI PSUs, many TVs, etc.
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KPPi
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Sun Jun 28, 2020 7:48 am

Similar problem here.

Pi4B used for few months.

Otherwise fabulous, but connecting to Samsung TV and old Samsung monitor (S20B300) has been biiiig problem.

Solved by using microhdmi to vga adapter.

Using original pi power supply

Both TV and monitor are two pronged, no earthing for whatever reason

Shock (definitely not static) when connected to both TV and monitor.

Recently vga adapter apparently fried.

Shock when microhdmi connected to tv or when connected to monitor.

No shock when pi not connected with hdmi to said tv or monitor

No shock when hdmi cable plugged into pi and not connected at other end

Not an electrical engineer but feel it is tv or monitor related problem

Thanks

P.S. edited to include Monitor model in case useful. Thanks for all suggestions!
Last edited by KPPi on Thu Jul 16, 2020 5:40 pm, edited 1 time in total.

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mahjongg
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Sun Jun 28, 2020 12:42 pm

KPPi wrote:
Sun Jun 28, 2020 7:48 am
Similar problem here.

Pi4B used for few months.

Otherwise fabulous, but connecting to Samsung TV and old Samsung monitor has been biiiig problem.

Solved by using microhdmi to vga adapter.

Using original pi power supply

Both TV and monitor are two pronged, no earthing for whatever reason

Shock (definitely not static) when connected to both TV and monitor.

Recently vga adapter apparently fried.

Shock when microhdmi connected to tv or when connected to monitor.

No shock when pi not connected with hdmi to said tv or monitor

No shock when hdmi cable plugged into pi and not connected at other end

Not an electrical engineer but feel it is tv or monitor related problem

Thanks
A TV/Monitor that doesn't have a ground prong, but still has filter caps from mains to chassis should NOT be sold, as its obviously dangerous.

The only real solution is to add the ground wire somehow, between the chassis of the TV and a local earth pole. For example you could use one of the screw-holes of a VGA or other D-SUB like connector and screw a wire to it, and connect the other side of the wire to the ground prong of an outlet, or to a water pipe of some sort.

And yes, the mains leak current can blow up any electronics you place in-between the electrical wiring between the voltage on the TV, and a place where the current can flow to earth.

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davidcoton
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Sun Jun 28, 2020 1:29 pm

mahjongg wrote:
Sun Jun 28, 2020 12:42 pm
you could use one of the screw-holes of a VGA or other D-SUB like connector and screw a wire to it, and connect the other side of the wire to ... a water pipe of some sort.
If you try this, you need to make sure that it is a continuous metal water pipe. No plastic pipes inserted and not a gas pipe (it has happened).
An ineffective earth connection just spreads the problem further.
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drgeoff
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Sun Jun 28, 2020 2:13 pm

mahjongg wrote:
Sun Jun 28, 2020 12:42 pm
KPPi wrote:
Sun Jun 28, 2020 7:48 am
Similar problem here.

Pi4B used for few months.

Otherwise fabulous, but connecting to Samsung TV and old Samsung monitor has been biiiig problem.

Solved by using microhdmi to vga adapter.

Using original pi power supply

Both TV and monitor are two pronged, no earthing for whatever reason

Shock (definitely not static) when connected to both TV and monitor.

Recently vga adapter apparently fried.

Shock when microhdmi connected to tv or when connected to monitor.

No shock when pi not connected with hdmi to said tv or monitor

No shock when hdmi cable plugged into pi and not connected at other end

Not an electrical engineer but feel it is tv or monitor related problem

Thanks
A TV/Monitor that doesn't have a ground prong, but still has filter caps from mains to chassis should NOT be sold, as its obviously dangerous.

The only real solution is to add the ground wire somehow, between the chassis of the TV and a local earth pole. For example you could use one of the screw-holes of a VGA or other D-SUB like connector and screw a wire to it, and connect the other side of the wire to the ground prong of an outlet, or to a water pipe of some sort.

And yes, the mains leak current can blow up any electronics you place in-between the electrical wiring between the voltage on the TV, and a place where the current can flow to earth.
As I already wrote in the second reply in this topic: "..one of the reasons that operating manuals for TVs, set top boxes etc invariably tell you to connect all pieces of a system together before plugging any of them into the AC sockets."
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mahjongg
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 12:08 pm

Unfortunately plugging all devices into a common power bar will not really help, as with two-prong plugs you can simply rotate the plug 180 degrees, and switch the "hot" and "cold" wires to the plugged in device, meaning that there can still be a huge voltage difference between one device's chassis, and the other devices's chassis.

you really need at least one device plugged in with a three-prong plug, into a grounded outlet, so the leakage current can flow to ground safely.

and yes, I totally agree that the "ground point" you are connecting the TV's chassis to should be a reliable connection to ground, It would be horrible if you try to use a metal gas pipe, with an incomplete connection to ground, an electric spark and gas isn't a safe combination :twisted: :roll: . Use common sense!

here is a site that explains the problem, with an easy to understand picture:
https://www.meanwelldirect.co.uk/glossa ... e-current/

Image

L = Live and N=Neutral if E (Earth) is not connected, the leakage current flowing through the 2n2 capacitors connected to L will flow into the chassis (dotted line) which is connected to the GND of the device, instead of flowing to earth through the E wire.

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 12:35 pm

mahjongg wrote:
Tue Jun 30, 2020 12:08 pm
Unfortunately plugging all devices into a common power bar will not really help, as with two-prong plugs you can simply rotate the plug 180 degrees, and switch the "hot" and "cold" wires to the plugged in device, meaning that there can still be a huge voltage difference between one device's chassis, and the other devices's chassis.
Are your 2 prong plugs not "keyed", via different width plug blades, that guarantee orientation into receptacles with keyed openings?

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 12:40 pm

bjtheone wrote:
Tue Jun 30, 2020 12:35 pm
mahjongg wrote:
Tue Jun 30, 2020 12:08 pm
Unfortunately plugging all devices into a common power bar will not really help, as with two-prong plugs you can simply rotate the plug 180 degrees, and switch the "hot" and "cold" wires to the plugged in device, meaning that there can still be a huge voltage difference between one device's chassis, and the other devices's chassis.
Are your 2 prong plugs not "keyed", via different width plug blades, that guarantee orientation into receptacles with keyed openings?
There may be countries where that will be the case, but only some, most often you can plug in the plug either way. I don't think US plugs have any protection for plugging in plugs "backwards". At least none of the ones I have ever seen did. The only ones I have ever seen were unpolarised
Image

as are the common "europlug" ones, but those are only used with equipment that has no filter caps to its chassis.
Image

all kinds of solutions for this problem exist, have a look here: https://en.wikipedia.org/wiki/AC_power_ ... nd_sockets

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 12:51 pm

Most (all?) 240V countries have keyed plugs. 120V countries' standards are -- pun only semi-intentional -- shocking. And amazingly dangerous. Someone here (I forget who, sorry) posted a photo of a 6-way US-style extension lead. That's *90A* total potential current draw, and was, AFAICT, unfused. It's insane.

https://www.worldstandards.eu/electrici ... d-sockets/ is a good reference site.

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 2:23 pm

dickon wrote:
Tue Jun 30, 2020 12:51 pm
Most (all?) 240V countries have keyed plugs. 120V countries' standards are -- pun only semi-intentional -- shocking. And amazingly dangerous. Someone here (I forget who, sorry) posted a photo of a 6-way US-style extension lead. That's *90A* total potential current draw, and was, AFAICT, unfused. It's insane.

https://www.worldstandards.eu/electrici ... d-sockets/ is a good reference site.
Some old tube (valve) TV's and stereo equipment had neutral connected to chassis which was dangerous if they did not have a polarized plug or the house wiring were reversed. Haven't seen one of those in 4 or 5 decades.

Modern 'double insulated' appliances are not required to have polarized plugs.

It is not possible to draw 90A (6*15A) from an outlet extension. The outlets are wired parallel so the max combined current draw can be no more than the mains circuit breaker which is either 15A or 20A.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 2:48 pm

mahjongg wrote:
Tue Jun 30, 2020 12:40 pm

There may be countries where that will be the case, but only some, most often you can plug in the plug either way. I don't think US plugs have any protection for plugging in plugs "backwards". At least none of the ones I have ever seen did. The only ones I have ever seen were unpolarised
as are the common "europlug" ones, but those are only used with equipment that has no filter caps to its chassis.
all kinds of solutions for this problem exist, have a look here: https://en.wikipedia.org/wiki/AC_power_ ... nd_sockets
In the US, you can find both polarized and unpolarized 2-pin plugs (and extension cords). The 'slot'' for the non-live terminal of a standard US 3-pin socket is somewhat longer than that for the live terminal, so the earth pin is not essential for orientation. The unpolarized plugs and corrds are supposed to be used only for lighting circuits, where polarization should not matter (as long as you don't touch the screw component of a reverse-connected light bulb!). It should also not be possible to plug a polarized plug into an unpolarized extension cord, but it frequently is, if you push hard enough :) . The situation isn't quite as bad as you implied, but it is far from ideal.

drgeoff
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 3:12 pm

Chassis connected to either side of mains is not really the issue as that practice has virtually disappeared. The issue is the either the capacitive voltage divider in mahjongg's diagram above or the single capacitor between the input side of a switch mode PSU and the "0 volt" of the DC output. The leg of the capacitor on the input side is connected to the negative output of the input bridge rectifier and thus is at "half mains". In neither case does reversing the live and neutral make any difference so polarising a two pin plug does not help.

Mahjongg's diagram is not just theory. Here is the mains input of a piece of AV equipment from a top name brand.
Attachments
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business_kid
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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 3:36 pm

You're right - it's badly organised. Most lethal shocks are left --> right hand, or left arm --> right (& perhaps left) foot, because that way, they pass through the heart.

It's important to note that 110/120V systems are in fact ±55V/60V with reference to earth. This means 110V only appears between the 2 live leads. As most shocks are to earth, this doesn't make it half as bad.

In the European 220/240 based system, one of the live wires is at/very near 0V to ground. Earth is ground, and live is 240V away. So we have Live, neutral, & earth. Earth is a local earth (often on an 'earthing pole' or pipe), neutral is earthed at a generating station. Ours was a much more dangerous system, so there's a "CE" Mark that everything must have to be sold. That served to wipe out bad practises.

We also must fit premises with an RCD - a Residual Current Device. It measures the current between live and neutral, picks up a tiny difference(15mA?), and turns all power off if it happens. That's because the current is leaking through earth, or through someone! When I fitted an RCD in my house, it kept tripping. I eventually found a neutral --> earth fault in my cooker. But in shocks, don't underestimate static - walking on a synthetic carpet or while wearing synthetic clothes can build up to 20KV of static electricity. That's why ICs and Circuit boards have anti-static wrapping. Electronic engineers & technicians put on 'earthing straps' before they start work.

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 4:36 pm

klricks wrote:
Tue Jun 30, 2020 2:23 pm
Some old tube (valve) TV's and stereo equipment had neutral connected to chassis which was dangerous if they did not have a polarized plug or the house wiring were reversed. Haven't seen one of those in 4 or 5 decades.

Modern 'double insulated' appliances are not required to have polarized plugs.
some 15-20 years ago, my dad blew up one of our CRT tv's by just plugging it in
the hot/neutral was backwards on the socket, and the plug for the tv was keyed to only go in the "right" way
but "neutral" was tied to the coax line, so just plugging it in shorted things out

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 5:18 pm

business_kid wrote:
Tue Jun 30, 2020 3:36 pm
It's important to note that 110/120V systems are in fact ±55V/60V with reference to earth.
That is true in some European construction sites where isolation transformers are center-earthed to provide reduced low voltage.

It is not generally true in native 120V countries. To provide for high power loads they have two or three phases that are 120V to earth and 208V or 240V to each other.

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 7:17 pm

jojopi wrote:
Tue Jun 30, 2020 5:18 pm
business_kid wrote:
Tue Jun 30, 2020 3:36 pm
It's important to note that 110/120V systems are in fact ±55V/60V with reference to earth.
That is true in some European construction sites where isolation transformers are center-earthed to provide reduced low voltage.

It is not generally true in native 120V countries. To provide for high power loads they have two or three phases that are 120V to earth and 208V or 240V to each other.
Yes! In the US, for example, the return wire (for a 120V, single phase, circuit) is tied to ground at or near the main breaker box.

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Re: Getting shock from micro hdmi port when connected to tv hdmi port

Tue Jun 30, 2020 9:50 pm

business_kid wrote:
Tue Jun 30, 2020 3:36 pm
In the European 220/240 based system, one of the live wires is at/very near 0V to ground. Earth is ground, and live is 240V away. So we have Live, neutral, & earth. Earth is a local earth (often on an 'earthing pole' or pipe), neutral is earthed at a generating station.

We also must fit premises with an RCD - a Residual Current Device. It measures the current between live and neutral, picks up a tiny difference(15mA?), and turns all power off if it happens.
Based on UK regulations and practice:
  • The conductor at 240V potential is correctly called "Line". Line and Neutral are both referred to as "live".
  • There are three different common earthing arrangements. Only "TT" has a local earth as the main earth connection. The other two schemes have an earth at the supply substation, either of the neutral (TNC-S) or on a separate conductor (TNS). TNC-S may have a local earth rod as a supplementary measure, this has the disadvantage that under supply-side fault conditions it can carry extremely high currents.
  • RCD protection is now compulsory for TT supplies, and for most socket outlets and lighting circuits on any supply. There is no obligation to retro-fit older circuits, but such protection is strongly recommended.
  • The standard protection is for a current imbalance of 30mA. In practice RCDs will trip at 15-25mA, sometimes less. This provides "life protection" in most cases.
  • RCD protection on older systems would switch off the whole installation. Circuits must now be put into at least two separately protected groups, best practice is to protect each final circuit individually.
Sorry that's all a bit technical, but understanding what RCDs do (and don't) provide and how safety is achieved on mains systems is important.

EDIT: It is relevant to add: if your supply has an old, black trip marked "Voltage Operated ..." or "VOELCB", usually placed between the meter and the fusebox, it should be replaced AS SOON AS POSSIBLE ... such devices can fail without warning and in doing so can result in earth being disconnected, which makes any Line to Earth fault potentially lethal. If in doubt, consult a qualified electrician.
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