Will plug and unplug Computer and Monitor causes computer to hang up and crash

[Wilson__]

When both Computer and Monitor use 2 pins double insulated power supply (without PE Protective Earth, the big Earth pin on AC power socket), will plug and unplug cable between them causes computer to hang up and crash due to the in-rush current between the two units that are 'floating' and not at same potential relative to the Earth (the soil under our home)?

I refer to UK electricity code.  USA has different arrangement for protectie earth.  There are formal documentation (I do not have detail head) stating that using USA wiring practice text book causes violation and fire hazard in UK due to the difference.

UK 2 pins socket has fixed L and N and cannot be plugged the other way round.  Wonder if this matters to the in-rush current?

Seem this is an example for the Y cap circuit

[Wilson__]

Sorry.   Added I clarify referring to UK electrity code.

[Someone]

will plug and unplug cable between them causes computer to hang up and crash

Shouldn't, but can.
Crap built products are out there.

[Wilson__]

Sorry.  I clarify that the Computer and Monitor are top few well known brands.

[SteveThackery]

Well, it never has for me.  As for whether it theoretically could, I don't know but I doubt it. After all, hot-plugging of almost everything to everything else is the established norm, so I have confidence that any risk of harm will have been designed out a long time ago.

[Gyro]

The Class-Y noise suppression capacitors (normally 2.2nF) between mains side and secondary of the power supplies will pass a steady state AC current of approximately 166uA on 240V 50Hz mains. This current is way too small to cause any hazard to humans or computer operation.

There is another factor though. If you happen to plug the monitor when the mains AC voltage waveform is at its peak, that same 2.2nF capacitor will pass a very much larger instantaneous charging current, limited by many factors, mains wiring impedance between the computer and monitor sockets, their mains leads, the DVI or HDMI cable between them etc. In this particular situation might cause a crash depending on the computer's EMC susceptibility what it's doing at the time, or any number of other factors. It's impossibly to say other than 'might'.

This factor is which manufacturers of A/V equipment, computer equipment etc, warn against hot plugging of interconnecting cables. This spike current can occasionally be seen as a tiny spark between connector shells when not following this warning (166uA would never cause a visible spark).

Now you are asking whether plugging the monitor mains connection will cause a hang or crash. I think this is very unlikely, much more so than hot plugging the DVI/HDMI(/VGA?) cable, but it's impossible to give an absolute assurance.

[Wilson__]

Googling and there seem at least 3 ways Y capacitor is connected.

Any idea if IEC of similar standard body has specify whether (a), (b) or (c) is used? 

(a) Output low volt DC Negative to Input High-voltage rectified DC Positive

(b) Output low volt DC Negative to Input DC Negative

(c) TWO Y capacitors with "mid-Point" connect to Output low volt DC Negative or Positive

I suspect maximum worst-case potential difference when two devices with (a) and (b) can be double the peak AC voltage. 

In my case of 220 volts AC, it can be 2 X 1.4 x 220 = 616 volts transient when Computer and HDMI Monitor cable is plugged in.   In my case, the UK plug L and N cannot be swapped. 

In theory, transcient current peak and waveform will depends on cable inductance, etc.   

In theory, transcient will affecct circuit of the Computer after coupling mechanism, Magnetic induction or voltage coupling via stray capacitance.

Also a thread in this forum https://www.eevblog.com/forum/beginners/raspberry-pi-and-floating-gnd/] [url]https://www.eevblog.com/forum/beginners/raspberry-pi-and-floating-gnd/[/url]

[Gyro]

The third one is only normally used where there is a 3 pin input filters - they return to the mains earth.

There is no 'standard' way to implement the primary-secondary cap. The Y cap is a certified high breakdown voltage (several kV) part so it makes no difference in that sense whether it connects to the primary side positive or negative - although primary positive is probably more common due to the shorter RF path. It is a matter of optimizing the EMC emmissions of the PSU which also takes in the switcher, transformer design, PCB layout etc.

As I say, It's not something that the standards bodies would have an interest in, other than the safety approval rating of the parts and the Low voltage Directive (and EMC) compliance as part of CE/UKCA approval.


P.S. For safety's sake, the first two diagrams are misleading as they show Neutral connected to an Earth symbol. This, of course should never happen in the PSU, in fact the only place it can happen is at consumer unit in TNC-S mains supply installations.

[Wilson__]

These two say spark when cable plug/unplugged.

https://www.avforums.com/threads/hdmi-sparks-and-shocks.2169637/

https://superuser.com/questions/440959/is-hdmi-hot-pluggable

Googled and many say HDMI has 'hot plug detect pin' and 5-volts low voltage pin and hence can hot plug.  But, this is not about leakage current via the Y capacitor and would be fine in typical (older) equipment with metal case and PE Earth pin.

Long ago, since the original IBM PC, many PC follow the same design, with metal casing and connects to PE Protective Earth, the bigger pin on 3-pins AC socket.

In recent time, double insulation is getting popular and is 'safer' since no Earth pin needed and double insulation means the insulation is rated at higher voltage.  Just checked, my well known brand TV and ink jet printer/scanner are both 2 pins. 

[Wilson__]

primary positive is probably more common due to the shorter RF path

Could you please enlighten more or this is specific to certain 'generally used popular' PCB layout component placement design?

[Wilson__]

the first two diagrams are misleading as they show Neutral connected to an Earth symbol. This, of course should never happen in the PSU

Yes, true, for double insulation class, it should be isolated and with Y capacitor for ESD discharging. 

AC "Output low volt DC Negative"may be better description.

[Gyro]

primary positive is probably more common due to the shorter RF path

Could you please enlighten more or this is specific to certain 'generally used popular' PCB layout component placement design?

That's a complex subject, as is proper SMPS design in general. In simple terms, with the primary positive implementation, the Y cap is effectively placed across (and close to) a primary winding pin and a secondary winding pin on the transformer, across the safety isolation barrier. This is normally more effective in suppressing high frequency switching noise being coupled through the transformer from the switching node.

The primary negative implementation requires much more careful layout as the Y cap is connected close to the switching FET [Edit: drain, oops, Source], so could couple noise rather than reject it if there is any shared current path with the FET. Again, these are generalizations that don't take account of the design of the transformer, but this option is probably harder to implement successfully (ie. number of iterations of implementation and EMC testing).

[Someone]

It's impossibly to say other than 'might'.

This factor is which manufacturers of A/V equipment, computer equipment etc, warn against hot plugging of interconnecting cables. This spike current can occasionally be seen as a tiny spark between connector shells when not following this warning (166uA would never cause a visible spark).

Now you are asking whether plugging the monitor mains connection will cause a hang or crash. I think this is very unlikely, much more so than hot plugging the DVI/HDMI(/VGA?) cable, but it's impossible to give an absolute assurance.

OP is light on specifics and doesn't seem to want to read the manuals. Even protectively earthed monitors (as the "top few"/professional kind are) have the same warnings about powering everything off and/or unplugging before interconnecting:
"Power off your computer and all attached devices, then unplug the computer power cord"
"Turn Off your computer and disconnect the power cable."
"Before connecting the product, make sure you remove the power cords from both the product and the external device to prevent damage to the product due to a short circuit or over current."
So while there is not going to be a risk to the safety of the end user, the manufacturers specifically state there could be damage to the devices if interconnected while plugged in and power applied. Most consumer connectors are not designed or tested for hot plugging and there is no guarantee the grounds will connect first.

Predict the OP will now continue to convince themself that everything is fine and there are no risks from hot plugging.

[Geoff-AU]

Shouldn't, but can.
Crap built products are out there.

Or just an unlucky combination.  I have a monitor here made by a very large computer manufacturer and it regularly drops sync when I turn other mains loads on and off.  Screen goes black for about 3 seconds then it comes back on.  But it's rare.  It's the first monitor I've come across since LCDs took over that seems to be overly sensitive.

[Wilson__]

Re-read my new monitor manual, it says, remove power cord.

Switching off at device front panel does not work.  Many are put on standby mode and still running inside.  Switch off at "power distribution socket bar" not work as it only isolate the Live/Line wire.  N line still connected.

Manual says:

"2  Before connecting the product, make sure you remove the power cords from both the product and the external device to prevent damage to the product due to a short circuit or over current.
 
3   After all signal cables have been properly connected, connect the power cords back to the product and the external device."