Grounding of an AC-DC-AC circuit for use in providing stable AC voltage for use internationally

Question

I am hoping that someone can give me some guidance on a project I have been working on which has a single unresolved question.

For context to the question which I shall propose further on in this post, here is the purpose of the project:

I have multiple devices which are relatively sensitive equipment, I travel often with the all over the world, often being in another country every day or two.

This has obvious implications given that over the course of a week, the equipment can have AC supply voltages of 100 V 60 Hz through to 240 V 50 Hz and every combination in between, sometimes within the same day.

Each of the devices (except one) requires manually changing voltage input, most of them are internal, one even requires changing frequency due to the internal power supply of the device.

Last year I got sick of continuously having to deal with this as it was such a massive time sink each day, so I built an AC-DC-AC supply using a switching PSU which is directly connected to a TSW inverter.

The components used in this setup are as follows:

MEANWELL RSP-1000-27 This unit is a switching PSU which draws 12 A 100-240 VAC using either 50/60 Hz and outputs 37 A at 27 VDC

MEANWELL NTS-450-224 This unit is a true sine wave inverter which draws 25 A 22-31 VDC and is setup to output 1.9 A at 240 VAC 50 Hz

The DC-DC connection between the output of the switching PSU and the input of the inverter is using 10 cm of 6 AWG using properly terminated ring terminals for those wondering. Fuses and switches have also been employed in obvious places to avoid inrush issues during power-up.

Total draw on the 240 VAC output above with all the equipment I use attached only draws approximately 900 mA, the inrush on power up of all connected devices measuring approximately 1.5 A total. All well within the tolerances of the components.

I have been using this around the world without any issues to date with great success so far, but this has been powering the devices using the output of the inverter with a floating ground. This does not cause any issues to the devices given the nature of their use, but from a safety perspective it has been something in the back of my mind. I am currently in a position to address this but require some input from some electrical engineers to find the best possible solution - if one is even needed.

Now, the final details which will lead into my question if you are still with me:

The switching PSU obviously has a ground wire to its input sourced from the local AC supply wherever I am on any given day, as it should. The inverter has a grounding lug on the chassis which from what I can ascertain under "normal" operating circumstances be connected to ground via an earth stake or similar.

In the MEANWELL technical bulletins that I have been able to get hold of for their TSW devices, it states that the best practice would be to ground the inverter using a ground stake when being driven from a battery or other DC source in a remote location not tied to a building or to mains.

However, it cautions against grounding the inverter to any AC grid mains as there will likely be complications from the mains neutral to ground link which would compromise the intended safety aspect of grounding the equipment connected to the output of the inverter. Given the inverter has an internally bonded ground & neutral I would consider that grounding the chassis's of the devices connected to the output of the inverter would not be needed, which is how the setup is currently configured.

The question: For safety's sake what would be the best practice to provide an RCD style protection? Consider an example of why to be: a glass of water gets accidentally spilt into one of the pieces of the equipment connected to the AC output of the inverter.

Thanks to anyone for taking the time to read the above, I understand that it is long winded for a question that may seem trivial, but this is something I cannot find any information on and wanted to provide as much detail as possible to frame the question as I want to approach this in the correct way, from a safety standpoint.

Answer 1

As your power source is doubly insulated, one phase or the other could short to the ground without any issue and similarly with a personne.

What a better protection?

(Please note that connecting the inverter earth lug to the ground do nothing here has you have no existing current return loop except the small capacitive or sadly an insulation fault of the inverter).

You have got your own 'independent' power system and the question is about which grounding system should apply.

As voltage and frequency varies around the world grounding system could also vary. See grounding systems as per IEC 364.

If you want to adopt e.g. a TN-S grounding system you must deliberately connect one of the output phase to PE and bond the inverter ground lug to the local ground (by default the socket wall ones). In this case a Residual-Current Device make sense.

A better approach could check periodically the effectiveness of devices insulation or even a monitored IT grounding system but the latter is a little 'high end'.