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How is the Prusa Original Enclosure grounded?  

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vinansky
(@vinansky)
Active Member
How is the Prusa Original Enclosure grounded?

Folks, I don't see where the "tin can" is grounded. Looks as if the grounding is isolated to the printer if there are no addons. If you look at the Auxiliary PSU, it appears to attempt to ground via the  two star washers. Does anyone more knowledgeable than I, explain if or how it grounded. Seems like a safety issue to me --- potential for a large capacitor waiting to discharge.

Please enlighten

St George

Posted : 17/11/2023 2:14 am
Johntron
(@johntron)
Active Member
RE:

Good question . Appliance chassis are typically grounded to prevent a "live" chassis - one inadvertently connected to the "live" wire of the power outlet.

The typical scenario would be a loose screw-down terminal allowing one of the conductors from the wall to touch the chassis. In this case, if the chassis is connected to (true) ground, electricity would take this instead of through a human.This is more of a concern where the appliance uses high-voltage (not just at the plug) like a washing machine with a giant motor (or 3D printer with heated bed).

In systems where there is no ground wire on the plug, I believe the solution is double insulation. High voltage systems (e.g. screw-down terminals) would be insulated or covered somehow, and the chassis would also be electrically isolated from these systems (plastic standoffs, plastic brackets, plastic covers, etc). AFAIK, "high voltage" only applies to devices operating over some voltage/current/power threshold (like >12V, >1A, or >25W).

I believe some certifications actually require grounded enclosures AND double insulation, because in a worst-case situation, you could have two problems: a "live" chassis and a break in the connection to ground. In this case, double insulation would be the only thing preventing electrocution.

I just ordered MK4 and enclosure, so I can't comment on this configuration.

This post was modified 3 months ago by Johntron
Posted : 24/11/2023 10:13 pm
Chip
 Chip
(@chip)
Active Member
RE: How is the Prusa Original Enclosure grounded?

I've seen several threads where people are adamant that no additional grounding is necessary.  I have also seen my display blank, and my system reboot after a static shock.  Also have you noticed that whenever you move any of your motors the LCD lights up.  Is this due to a current generated by the motors suddenly working like a generator?  Both leave me slightly concerned about whether the system is grounded properly.  Also when discussing it, remember there is a difference between an earth ground and the neutral wire.   The neutral wire completes the circuit.  The ground wire is a safety component that gives a safe path ( or at least safer than through you )  to ground for any current applied to an unexpected location.  Also please remember there is a difference between AC current and DC current.  The AC from our walls is converted to DC in the printer.  I believe it is safe to say that no item outside of a planned circuit should ever touch the wiring in a circuit.  So I would not ever consider grounding anything to the neutral of a circuit.  I do believe there is a case to be made for having the printer and the enclosure properly grounded to an earth ground, I believe a static charge may have taken out the ethernet port on my MK4 earlier today.  

Posted : 29/11/2023 9:29 pm
Chip
 Chip
(@chip)
Active Member
RE: How is the Prusa Original Enclosure grounded?

There needs to be a way to ground the mk4 in the original prusa enclosure.  It's winter here and with the colder temperatures and reduced humidity, I get a static shock every time touch metal.  Unfortunately, sometimes that is my Prusa enclosure.  Whenever I get a static shock by touching it, my MK4 resets.  The screen goes blank and it reboots.  today it happened in the middle of a print.  Thank goodness for the crash recovery on it,  After rebooting, it started right back up where it left off.  But this can't be good for the printer.  Remembering to touch something metal before I touch the enclosure is not a viable answer.  The static shock should be directed to ground somehow and not through to the printer.  

Prusa support!!  We need a resolution to this.

Posted : 15/12/2023 7:31 pm
Johntron liked
ronnie12342003
(@ronnie12342003)
Estimable Member
RE: How is the Prusa Original Enclosure grounded?

surely you can bolt a cable on it and ground it ?

Posted : 15/12/2023 8:42 pm
Chip
 Chip
(@chip)
Active Member
RE: How is the Prusa Original Enclosure grounded?

We have been told in other threads not to do that.  So I'm looking for Prusa technical support to give us a solution that properly grounds the printer and the enclosure.  I agree it should be as simple as attaching a screw to the enclosure, the printer and the chassis ground but Prusa has said that it will screw up the printers electronics.  I don't see how that's possible unless they are somehow using the printers chassis as part of the grounding circuit for their electronics.  But I'm want a Prusa approved mod/answer.

Posted : 15/12/2023 9:46 pm
Johntron
(@johntron)
Active Member
RE: How is the Prusa Original Enclosure grounded?

 

Posted by: @chip

I get a static shock every time touch metal.  Unfortunately, sometimes that is my Prusa enclosure.  Whenever I get a static shock by touching it, my MK4 resets.  The screen goes blank and it reboots.  today it happened in the middle of a print.  Thank goodness for the crash recovery on it ...

OK now that's interesting. Now I understand that the issue is electrostatic discharge (ESD) interfering with normal operation not grounding for (human) safety.

If the electronics are rebooting, it seems like: a) the ESD is triggering the power panic functionality, b) an electrical path exists between enclosure and buddy board that bypasses ESD protections, or c) ESD protections in the buddy board are insufficient.

Judging by the following comment, it seems like A:

Thank goodness for the crash recovery on it,  After rebooting, it started right back up where it left off.  But this can't be good for the printer. 

If so, this shouldn't harm the printer, but would obviously be annoying. If it were B or C, I would expect the electronics to fail (permanently) with the first shock - or if you're extremely lucky, to simply go into a corrupted state requiring manual intervention.

According to some comments on Prusa's GitHub pages, it seems Prusa had the PSU manufacturer, Delta Electronics, incorporate power panic circuitry into one of Delta's PSU's. I would trust both Delta, Prusa, and the safety organizations that certified the devices for use in Germany and US to all do their diligence on designing for safety, but maybe there was no easy way to avoid power panic when ESD occurs.

FYI grounding wouldn't prevent ESD from your body through the device - it would only provide a safe return path; there would still be a massive transient (thousands of volts) through the enclosure to ground. This is unavoidable due to physics; however it might be possible to mitigate the pain / sensation with better design.

Posted : 16/12/2023 4:40 am
Pedroid
(@pedroid)
Trusted Member
RE: How is the Prusa Original Enclosure grounded?

Just a side note: The grounding is not a safety feature designed to protect the human operator but the electric installation of the house. The fuse is usually 250V/16A which doesn't react when - let us say - 15A flow through your body for 10 hours. Only in new installations an additional fuse exists which measure the current that flows into the circuit equals the current that flow out of the circuit. Dunno the correct english name for it. Deepl propose "residual current circuit breaker". At least in germany such a circuit breaker doesn't exist in old installations. Than came a period in which the circuit breaker was mandatory for bath rooms, and i believe in new buildings nowadays it is mandatory for each circuit but there exists no order for older installations to upgrade.

Posted : 16/12/2023 10:14 am
Chip
 Chip
(@chip)
Active Member
RE: How is the Prusa Original Enclosure grounded?

in the US that is a GFI or ground fault indicator circuit. It is mandatory on out door circuits or circuits near water. It is not what I’m asking for here though. What I’m asking for here is protection for the electronics from a static charge that results when i touch the chassis. 

Posted : 16/12/2023 12:46 pm
Chip
 Chip
(@chip)
Active Member
RE: How is the Prusa Original Enclosure grounded?

Exactly. The pain from the shock is annoying but not my concern. My concern is it can’t be a good thing when something with panic in the name is triggered frequently. 

Posted : 16/12/2023 12:52 pm
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