Duet 3 GND header

oliof

Hi,
My V core pro has all GND on the AC. I wonder if/when/where to connect the GND header on the duet3 board (I have a revision 0.6 board)? It seems like a bad idea to tie DC GND to AC GND ...

DocTrucker

On an AC heater you should have live, neutral and ground. You should connect as much of the metal work of your printer as possible to a good ground. That includes the heat spreader on the heated bed.

I need to have a look again but didn't think the Duet3 was designed to take AC voltage directly and that an AC heatbed should be modulated by an external SSR, but I maybe mistaken.

DocTrucker

I think general advice is to tie all negative DC power supplies together, and you may find that the Duet3 does that anyway. Tying DC negative to mains earth is advised by some. Largely dependant on what PSUs you are using.

DocTrucker

Miss read your post. You were posting about tying dc negative and ground/earth, not in context with AC heatbeds, sorry!

Somewhere in the history of my posts someone responded with a good filtwr circuit to allow dc negative and earth to be tied if there were a voltage build up, but otherwise remain seperate relying on the filters in the PSUs. I will try to fing it.

dc42

I recommend tying DC negative to mains ground for safety reasons, in case the PSU develops a fault. However, if you use a USB connection between the Duet and a PC, you need to be careful of creating a ground loop.

oliof

@dc42 so the GND header on the duet3 is just another DC neutral header?

PS: I am not connecting anything via USB, the Raspberry is connected via the SBC connector/SPI. I do have a ground loop filter for USB connections though.

DocTrucker

Here's the discussion I had on it on this forum. Unfortunately the link appears dead.

https://forum.duet3d.com/topic/7582/meanwell-power-supply-ac-ground-and-v-connection/15

A Former User

DC neutral and AC ground are a bit ambiguous.

DC has negative and ground, which are both the same thing. (in the context of single rail suplies)

AC can have a neutral line which is not always quite the same as ground (but can be connected in some distribution systems).

AC/mains always have protective earth (PE) this is normally connected to DC ground, some power supplies can have a high impedance or capacitive coupling between DC ground and PE but I fully support having DC ground connected to PE with a direct low impedance connection.

oliof

@bearer the duet3 0.6 has a header labelled GND next to the Ethernet port. I am trying to figure out whether I should connect it or not. @dc42 seems to say yes, connect it to mains ground.

I really don't get why people keep bringing up neutral which is something different.

A Former User

@oliof said in Duet 3 GND header:

I really don't get why people keep bringing up neutral which is something different.

@oliof said in Duet 3 GND header:

so the GND header on the duet3 is just another DC neutral header?

because people get confused; and in TN distribution N is wired to PE, in TN-C the distribution even have a PEN conductor that is split into PE and N.

@oliof said in Duet 3 GND header:

the duet3 0.6 has a header labelled GND next to the Ethernet port. I am trying to figure out whether I should connect it or not. @dc42 seems to say yes, connect it to mains ground.

No, he said you should connect DC negative to mains ground/PE; and you should do that at the Vin terminal for the lowest possible impedance path to PE

Garfield

Cat among pigeons - fraid I can't agree with this one.

There is a lot of bad information out there about earth bonding - ground and earth are not the same thing.

If you earth bond the isolated low voltage side of an isolated power supply you just negated the reason for having an isolated supply in the first place.

The sort of voltages used in 3D printers are classed as ELV (mostly except for those with 240AC mains heaters) earth bonding is not required for almost all ELV (< 50V AC and < 120V DC). In fact bonding to earth can expose you to a shock hazard that otherwise would not exist because of the isolation, in SELV it is actually forbidden to ground the secondary side.

This is a huge topic but I won't be grounding my DC or 24V AC.

DocTrucker

@Garfield in your ideal set up would you connect all metalwork to the protective earth or DC negative? Likewise would you dump noise from cable shields to DC negative or protective earth? Finally is there a standard to look for that guarantees hazardous voltage build ups on the DC side either can't build up, or are dumped to protective earthe through a filter?

A Former User

I don't think the average DIY printer itself classifies as SELV (or PELV depending on grounding) as the mains supply is integral and requires terminating the mains voltage? If you had a external power brick then yes?

Combine with some cheap printer kits having supplies that lack or have faulty isolation and most modern wiring have a working GFI or RCD bonding the frame is probably safest for those who don't know to decide for themselves.

Garfield

It is probably best to earth bond the frame of any printer, not forgetting the bed as this deals with static electricity that is produced during operation, this allows it to sink to ground without going via your electronics.

I would not bond the frame to an isolated ground for this reason but a lot depends whether your power supply is an 'isolated' one or not - you may find its ground is already earth referenced if it isn't an isolated supply.

As for connecting cable shields / screens these really shouldn't be connected to an earth reference but bonded to the circuit ground. This topic could easily stray into RF generation and rejection and such, you absolutely must not ground a shield at both ends.

I think the part that many find difficult is that ground does not mean earth, ground is merely the reference point for the circuit itself, earth is something entirely different.

What is unfortunate is the standard of many low end PSU's, given the propensity of folk for seeking the cheapest they are likely to encounter some real nasty stuff that I believe isn't safe to use. I think a problem coming from this is that most people won't know how or be able to identify a poor PSU so 'erring on the cautious side is always preferred - if in doubt earth it.

My PSU for what it is worth is not part of, nor is it attached to the printer frame, yes my PSU chassis etc is grounded but it is not neutral referenced, so the AC it produces is floating and isolated. It is totally overengineered but that's the OCD in me.

(My PSU on the CoreXY is a Balluff BAE0003, on my Prusa I run a PULS SL20)

oliof

End result: I know nothing anymore and probably need someone with the knowledge to look at my rig at my place and tell me what to do ...

Garfield

Come now - you asked the questions, that's more than some do, so to say you know nothing is a little defeatist.

Electrickery is a subject that has it's share of complications for sure but nothing that can't be learned, you're aware enough to ask the correct questions so you do know something.

I'd keep the AC earth and DC grounds apart.

Power your DUET through a decent quality 12V or 24V DC Isolated power supply - Meanwell / Cosel aretwo brands that spring to mind that are pretty decent. Try to avoid the unknown cheapest you can find as it could be expensive in the long run.

I don't know that much about the CR10 and I'm not in Germany that often these days North or South, last trip was 4 years ago to Berlin.

What specifically is concerning you ? how do you power the CR10 currently ?

dc42

@oliof said in Duet 3 GND header:

@bearer the duet3 0.6 has a header labelled GND next to the Ethernet port. I am trying to figure out whether I should connect it or not. @dc42 seems to say yes, connect it to mains ground.

That tab is connected to the Ethernet socket metalwork. It is specifically for the situation in which the socket is right behind a hole in a metal enclosure, so that you can connect that tag to the metal enclosure to reduce EMI. The alternative is to use a spring tab to connect the enclosure to the Ethernet socket metalwork, as is commonly done on PCs.

Danal

@oliof said in Duet 3 GND header:

Hi,
My V core pro has all GND on the AC. I wonder if/when/where to connect the GND header on the duet3 board (I have a revision 0.6 board)? It seems like a bad idea to tie DC GND to AC GND ...

You received a lot of information and posted that you were overloaded with info but still did not know the answer to the original question ("...know nothing..."). Therefore, I've repeated your original question above and will try to be as clear as possible:

Connect your 24V power supply to VIN with stranded wire of at least 18 AWG or .8mm2. CRIMP, do not solder, "bootlace" connectors to ends that go under screw terminals.
If you have a 24V heated bed, connect "Out 0 Power In" to the 24V supply with wire sized for that bed. The fuse is rated to 15A (the board to 18A) so 14AWG or 2mm2 is very roughly the largest that will be used. Use the same gauge from "Out 0" to the bed.
If instead you have a mains powered bed, via an SSR (Solid State Relay), it is OK to jumper "Out 0 Power In" from VIN (careful with polarity they are 'backwards' in relation to each other) and then use 20 AWG or even 22 from "Out0" to the SSR low voltage input. ALSO, bond the frame of the machine to mains (earth) ground.
Use an isolated 24V supply if at all possible. Cheap ones usually are not isolated. Meanwell is a brand that usually is.

And, at last, the answer to your original question:

No need to connect the tab near the ether to anything.
WIth one exception: If the board is in a metal case, connect the tab near ether to that case.

And a bit of "best practice" with regard to ground:

Bring all grounds back to a single point. Do not 'chain' them. This is known as 'star ground'.
Normally, do not bond Low Voltage grounds to mains (110V or 220V) ground. That is also why the statements above about isolated 24V supply.

oliof

Thanks @dc42 and thanks @Danal -- I have done everything on your list, and as the board is not in a metal enclosure, I will ignore the Ethernet shield ground connector for now. I have a genuine Meanwell PSU so I am confident it is isolated.