Ground loops don't only affect 3D printers

dc42

See https://www.theregister.com/2020/09/11/on_call/ for an example of how ground loops can affect other equipment.

"The server had been possessed by a Microsoft hating demon and it needed an exorcism"

Isn't science a beautiful thing?

oliof

Reminds me of the classic http://catb.org/jargon/html/magic-story.html

zapta

I presume that 3D printers ground loops refer to this https://duet3d.dozuki.com/Wiki/USB_ground_loops#Section_Why_is_there_a_ground_loop .

My printer have the 24V circuits isolated from the grounded frame, similar to #4 in the above link. What is the reason that this is considered unsafe? Many of the appliances DC/DC power supply we use have isolated secondaries.

chas2706

@zapta said in Ground loops don't only affect 3D printers:

I presume that 3D printers ground loops refer to this https://duet3d.dozuki.com/Wiki/USB_ground_loops#Section_Why_is_there_a_ground_loop .

I was gobsmacked to read suggestion no.4 on avoiding ground loops:

Disconnect the power supply negative output from mains ground. For safety reasons, this is not recommended.

This suggestion is not only highly dangerous and stupid but would possibly warrant any house insurance null and void in the event of a fire caused by an electrical fault.

3DPMicro

Tail dragers can be equally frustrating because of a ground loop

fcwilt

@chas2706 said in Ground loops don't only affect 3D printers:

This suggestion is not only highly dangerous and stupid but would possibly warrant any house insurance null and void in the event of a fire caused by an electrical fault.

Why do you believe that is so?

Having the DC outputs of the power supply floating with respect to the AC ground is fine.

Frederick

theruttmeister

@fcwilt said in Ground loops don't only affect 3D printers:

@chas2706 said in Ground loops don't only affect 3D printers:

This suggestion is not only highly dangerous and stupid but would possibly warrant any house insurance null and void in the event of a fire caused by an electrical fault.

Why do you believe that is so?

Having the DC outputs of the power supply floating with respect to the AC ground is fine.

Frederick

Because Class 1 electrical devices (ie, ones with a connected earth pin) rely on a metal chassis/case with a low resistance connection to earth to protect in the event of an electrical fault.

Class 2 devices (ie, double insulated) do not have or require an earth connection, as they have additional insulation to protect them in the event of a fault.

Most small wall-wart power supplies I've seen are class 2, and if they have an earth pin its plastic because in the UK its needed to open the guards on the wall socket.

If you are in a workplace in the UK and you remove the earth connection on a Class 1 device, the PAT man is going to come around, find it, cut the plug off and say mean things about you.

The most likely risk is that you get a nasty shock when you touch the now un-earthed case... I agree that a fire is unlikely.
But someone burnt down their house with their modified Solidoodle, so you know, stuff happens.

fcwilt

@theruttmeister said in Ground loops don't only affect 3D printers:

The most likely risk is that you get a nasty shock when you touch the now un-earthed case

I said nothing about an "un-earthed case".

Of course you want the AC ground to be connected to the AC ground on any power supply that has such a connection.

You also want the AC ground to be connected to any metal parts (case, frame, etc) in case the AC hot or neutral could come in to contact with the metal parts and thus post a risk of shock.

But the DC outputs of the power supplies, as used in 3D printers, are almost surely isolated from the AC.

And given the low voltage they do not pose a risk of shock.

So there is no need to connect the DC negative output to the AC ground.

Frederick