Earthing problem in Monitor - Page 1
Forum section: electronics / beginners

author: 4kruby
author_rank: Contributor
timestamp: June 13, 2022, 05:29:50 am
content: Problem : When powered, some current sinks through the Earth pin.How I Found : The monitor was connected to the power outlet where the earth connection was not made (floating). Due to this, other equipemnts connected to the same power outlet (using a power strip), produces shocks (eg : connecting a soldering iron, tester glows on touching the body of the iron when monitor is ON and not when monitor is OFF).But when the same monitor is connected to a power outlet where the Earth wiring is done properly, this problem is not there.I wouldn't have detected this problem if the earthing was not missing from the power outlet. This was present from the beginning itself I guess. So, is this a problem?Or monitors usually send some current through the earth?Because, had the earthing been proper it would have been impossible for me to find this problemThanks

author: golden_labels
author_rank: Super Contributor
timestamp: June 13, 2022, 09:47:01 am
content: That is expected if earth is not properly connected.There are capacitors (Y-capacitors) between the power lines and earth. If earth is floating, they form voltage divider. For mains voltage of 230V AC that gives 115V AC present on earth. Those capacitors do not pass mains frequency well (50Hz range), so there is no trouble under normal operation. But if earth is floating and you touch it, that is enough to give you tingle.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 13, 2022, 09:49:29 am
content: This is (very likely) normal.A part of the power supply in the monitor is an filter, and this filter is connected with Y class capacitors to the earth connection.If the earth itself is missing, these capacitors form a voltage divider and half the mains voltage is present on the earth connection.In normal household appliances the capacitors are dimensioned in such a way that the current though the earth connection is small enough to not be dangerous and also does not trip the GFCI. (But it can be quite unpleasant when touched).Have a look into X-class and Y-class capacitors. Because these are safety related there extra safety regulations and certifications for them.You could measure the current between the earth connection of your monitor and the real mains earth with a DMM. It's likely just a few mA, and well below the trip current of an GFCI.

author: wraper
author_rank: Unknown
timestamp: June 13, 2022, 10:08:29 am
content: Quote from: 4kruby on June 13, 2022, 05:29:50 amIt's normal as said above and it's why you should not connect the equipment with earth in the plug into socket without proper earth. On top of that equipment which is earthed has lower requirements to insulation compared to double insulated equipment without the earth terminal (counterfeit chargers and cheap garbage have a very poor insulation anyway because they ignore any safety standards).BTW equipment without the earth terminal (especially with SMPS) often have these Y capacitors too between primary side and secondary GND. But they have lower capacitance in general and lower max permissible leakage current, so effect is less noticeable.

author: 4kruby
author_rank: Contributor
timestamp: June 13, 2022, 12:41:38 pm
content: Thanks much for your replies.I will read into the X and Y class capacitors. I was worried that I must replace the monitor.As I told, the switch board to which I connected this monitor - The electrician who installed a socket there, has forgot to connect the earth pin to the earth wire - the reason I was able to find out this phenomenon. There is no problem (even on the USB / HDMI ports) when I connect the monitor to a power terminal that is properly earthed!Thanks Again!

author: Terry Bites
author_rank: Super Contributor
timestamp: June 13, 2022, 04:26:04 pm
content: What kind of monitor- not vital signs I hope.Check your local standard for leakage currents IS 302-2 3.5mA?

author: 4kruby
author_rank: Contributor
timestamp: June 14, 2022, 04:36:15 am
content: Quote from: Terry Bites on June 13, 2022, 04:26:04 pmThis monitor -https://www.dell.com/en-in/shop/dell-24-monitor-s2421hn/apd/210-bdmo/monitors-monitor-accessoriesIt comes with inbuilt speakers.