TV HDMI connector is at 68 VAC compared to earth - Page 1
Forum section: electronics / general

author: mattko
author_rank: Contributor
timestamp: October 18, 2023, 06:26:18 pm
content: Hi all,I noticed that there is 68 VAC between the shield of HDMI port of my computer (earthed) and my samsung QE55Q80T TV shield HDMI (not earthed). I saw in the instructions of the TV that it is a class 2 product, so it does not require a connection to earth (and it doesn't have it). But there are some communication issues with the HDMI connection. Does anybody have an advice on how to solve this? I was thinking of earthing the HDMI shield at the TV side, but I'm not sure if this is a good solution. Honestly, I don't really get why the TV is not simply grounded...An important detail perhaps is that the flat where I live does not have a true earth connection, as only two cables come to the socket (line and neutral), so natural is connected to the earth terminals on the socket. It is a building from 1975. We have 230 VAC, 50 Hz.

author: langwadt
author_rank: Super Contributor
timestamp: October 18, 2023, 06:32:19 pm
content: neutral connected to earth in the socket? where on earth do they do that?

author: TimFox
author_rank: Super Contributor
timestamp: October 18, 2023, 06:55:13 pm
content: If the power-feed neutral is, indeed, tied to what should be "PE" at the socket, then the two capacitors at the power input of the device (line-to-ground and neutral-to-ground) will, indeed, make the "chassis ground" (connected to cable shield) see 1/2 the line-neutral voltage in series with a few nF of capacitance.Hence your measurement of 68 VAC from a 220 V power line.Do your local safety regulations allow that obsolete connection to remain on an older building?

author: SeanB
author_rank: Super Contributor
timestamp: October 18, 2023, 07:12:07 pm
content: Sadly yes, grandfathered in till you do any upgrade, which has to conform with current safety regulations. Simplest fix is to go grab a RCA plug, and use it as a way to get a good ground to the logic board, and connect to the case of the computer. Ground (outer) of the RCA cable plug to some 1mm cable, and then to a case screw of the computer, to provide a low imedance ground. Use one of the RCS inputs on the TV, likely video in, and centre pin is not connected. Have had to do that to audio equipment, to keep the cables from being current paths for noise, and not wanting to do a ground lift on the amplifier at all. Just used 1.5mm cable, so the impedance was lower than the audio interconnects.

author: mattko
author_rank: Contributor
timestamp: October 18, 2023, 07:18:06 pm
content: Quote from: langwadt on October 18, 2023, 06:32:19 pmSo the neutral is not connected to earth. Neutral is connected to earth terminals in the socket. So the metal case of a product would be connected to neutral.Quote from: TimFox on October 18, 2023, 06:55:13 pmA lot of wiring would have to be changed in order to have earth in all flats in the building. For sure it is not mandatory to change it.You won't believe that an electrician that I hired to do some minor wiring in the flat connected line to the earth terminals instead of neutral to earth terminals.Quote from: SeanB on October 18, 2023, 07:12:07 pmThanks. I was thinking of doing something like this. I will try it in the next days and let's see if the problem goes away. Sadly the computer is on the other side of the living room, so I will connect it to the socket earth terminal.

author: langwadt
author_rank: Super Contributor
timestamp: October 18, 2023, 07:18:32 pm
content: Quote from: SeanB on October 18, 2023, 07:12:07 pmhere many things are not earthed, either because sockets don't have earth, two pin plugs, or schuko which doesn't connect earth in our socketthe one things that often is earthed is the TV, via the antenna connection

author: themadhippy
author_rank: Super Contributor
timestamp: October 18, 2023, 07:27:22 pm
content: Quotein the uk places with the very rare tn-c (concentric earthing )wiring system, either wired in single core pyro or something similar to coax.

author: wraper
author_rank: Unknown
timestamp: October 18, 2023, 07:33:51 pm
content: Quote from: mattko on October 18, 2023, 06:26:18 pmThis has nothing to do with the voltage you measured. When TV is connected to grounded PC, it becomes grounded too. Most likely HDMI cable is either substandard garbage, not rated for needed pixel clock (resolution and refresh rate) you use, just faulty. Or is way too long for high pixel clock even if good quality. Also if image is disappearing occasionally, you may try powering PC and TV from the same socket. It may help, but again most it likely will just somewhat mitigate inadequate HDMI cable.QuoteIt's way, way worse than just not connecting earth. If neutral connection gets interrupted for any reason, all of your earthed equipment will suddenly become under mains voltage potential.

author: langwadt
author_rank: Super Contributor
timestamp: October 18, 2023, 07:36:37 pm
content: Quote from: wraper on October 18, 2023, 07:31:43 pmyeh, we've used for HDMI cable for other things and some cables are absolute junk; only half the grounds connected, wires with several Ohms resistance, etc.

author: wraper
author_rank: Unknown
timestamp: October 18, 2023, 07:43:53 pm
content: Heck, especially if your home uses a single phase, it's not that uncommon for some electrician to swap the wires and then you'll have a phase on all of your equipment. I guess your wiring is not even color coded.