Powering a monitor without earth/ground

Thread Starter

dman1487

Joined Dec 19, 2020
2
Hi

I have a monitor here for a portable project, and it needs to fit into the lid of a case. When it's in the metal cage, it's too thick and protrudes by about 10mm, not ideal.

My idea is to remove the board from the cage, 3D print a mount for it and attach it to the back of the screen. This will make it fit in easily.

The problem with this is there's a big ol' ground cable going from the earth pin of the plug to the chassis, and what looks like some plated screw holes. I'm worried the ground is completing the circuit, and if so that'll be a pain.

Is it safe to run without the earth cable? If not, are there any ways to get around it? Thanks in advance!

Bpoard2.jpgBoard1.jpg
 

KeithWalker

Joined Jul 10, 2017
1,393
It will be safe if the everything is well electrically insulated. A lap-top computer runs quite happily without a ground connection.
The metal cage may be there for RFI shielding so you may run into performance issues. If you do, you can probably correct it by using grounded alumimium foil for shielding.
 

Hymie

Joined Mar 30, 2018
924
Looking at the mounting screw holes on the PCB, not all appear to be electrically connected to earth via the PCB tracks. If the monitor is relying on these points to be earth/0V for correct operation it may not work when the metal cage is removed.

I would recommend you use a multimeter to confirm that the mounting hole PCB tracks that are electrically connected together are also connected with the cage removed. If not, you may need to solder jumper connections.
 

dendad

Joined Feb 20, 2016
3,657
One problem you may come across is the leakage to chassis via the power supply mains filter caps causing the chassis and common connection to rise to half the mains voltage.
It is at fairly high impedance, but can cause a zap and/or spark.
I have had devices killed by this voltage when connecting to powered up systems.
Often it is ok if all the connections are made before powering up, but just be aware of it as a possibility.
 

Ian0

Joined Aug 7, 2020
1,121
If it originally had an earth connection, then it is Class I, and does not have to meet as stringent insulation standards as if it were Class II (without an earth), so you can happily remove the metal provided you make it so that the pcb cannot be touched, but make sure that the pcb retains its connection to earth.
Check that those blue capacitors around the power input are not connected to earth. They are part of the EMC filtering, and often connect to earth.
 
The NEC prohibits normal circuit currents from flowing through the equipment grounding conductor ("objectionable current") - it is there only to provide a return path for fault current and keep exposed, normally non-current carrying metal parts bonded together at the same electrical potential - but more often than not it seems that product engineers wantonly disregard this. The number of timer switches, occupancy sensors, etc. I've seen which have utilized the EGC and the ungrounded circuit conductor to provide control power to themselves is ridiculous. What happens if conduit is used as the EGC and someone forgets to tighten a set screw or the pipe gets pulled apart during remodel? (seen it a dozen times.) 120V or 277V on the metal switch cover, that's what.

Point being, be careful and heed everyone's advice on this - or else the mistakes of whoever designed it might just come back to bite you.
 
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