First off, I'm a noob when it comes to hardware/electronics. Barely started and not planning on getting too deep in it.

I have a bit complex setup that boils down to multiple RPis (around 13, with possibility to add more in the future) and multiple 5V PSUs (not yet acquired, but I'm thinking at 10A a piece, some for powering the RPis, some for powering a bunch of relays, sensors, what not)

Is it ok to connect all the PSUs together at the negative ('-') pole in this kind of setup?

And is that sufficient for the RPIs (which would control the relay, sensors, etc (My previous related question))?

Or do I still need to connect all the GNDs on all the RPis together with the negative on the PSUs?

And does any "end" of it require any other components to make it safe/safer? Or better connect the RPis GND's to the actual earth ground? This part is really fuzzy. I found some explanations as to what is ground in electronics, like reference for measurement, but not really one that would explain the difference between earth ground and specifically the RPI ground pins (which have a reference 0V as I understand) and that in conjunction with the negative pole of a PSU/battery. Understanding this would probably allow me to answer myself all the previous questions. Maybe.


Thank you.

  • There is an alternative to wallowing in ignorance... maybe start here? – Seamus May 6 '19 at 14:05
  • That's some poor choice of words there. But thanks for the link. – ciuly May 7 '19 at 9:15
  • I'm voting to close this question as off-topic because should be sent to Electronics SE site – Seamus May 11 '19 at 0:54
  • Why close and not move it there directly? If they will be able to answer the main question of connecting PSUs and RPi GND pins together, I'm all for the moving it there. – ciuly May 11 '19 at 20:43
  • There seems to be a bug in the software here... I selected the "move" option. When the next panel was displayed, the only choice for where to move it was to "meta" (which was silly). And so, I selected an option for closure that allowed a recommendation - the recommendation was to move it of course. And your question seems to fit in Electrical better than it does here on Raspberry Pi. I hope that's clear. If not, please let me know. – Seamus May 11 '19 at 21:08

Your question is unclear.

If you intend to connect the Pi (other than by IP) then the grounds MUST be connected.

Other than that there is no need, although there should be no problems - provided you follow good practice i.e. no ground loops, single connection to a common point.

Connection to “real” ground is unnecessary and generally undesirable, as this can create other problems - but needs to be assessed on a case by case basis.

NOTE that it is illegal (in many jurisdictions) to connect to mains ground (unless the connected device is also powered through the mains connection).

In your comment you state "My problem with this single point things is that I have a 3-level house where I'm doing this, so getting a bunch of wires from all across the house to just 1 point goes into the madness zone in my head."

My answer was to the question you actually asked "Is it ok to connect all the PSUs together at the negative ('-') pole" If you intend to connect the Pi (other than by IP) then the grounds MUST be connected.

I pointed out some of the issues to consider.

I never said they had to be interconnected, indeed the contrary.

It is difficult to imagine a scenario where you could conceivable need 13 Pi, or why they would need to be interconnected; indeed I would not do this. I would not even contemplate feeding power between floors.

If you need to send data between machines there are reliable means of doing this.

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  • It is unclear because I have no idea what problems I may get into. I am trying to research first and apply good ideas, as opposed to test a bunch of options and maybe fry some components in the process. There will be no high voltage socket in less than 0.5m from any RPi, however high voltage cables (CYYF) do intersect (90 deg) both the low voltage ones and the FUTP ones that go to the RPi(s). However both low voltage and FUTP are in either plastic or metal tubes. There are also longer segments where they go in parallel but there's usually like 20cm gap between them. – ciuly May 7 '19 at 9:33
  • So I guess with that, earthing sholudn't be necessary. – ciuly May 7 '19 at 9:33
  • Regarding good practice: ground loops (after reading a bunch) is going to be an adventure given the multiple FUTPs I have all around the house. However "single connection to a common point" my googling doens't seem to get me a proper result. Can you elaborate or provide a good reading source? Thanks. – ciuly May 7 '19 at 9:44
  • I haven't the faintest idea what a FUTP is. Wiring is an art - learned after years of practice, and requires detail knowledge of what is being connected. Select a single point as ground reference - typically near the main power supply, and connect all others to this. The ground connections can be branched - use common sense when routing wiring. In complex cases isolation is a good idea. – Milliways May 7 '19 at 11:56
  • FUPT is a network cable (foiled/unshielded twisted pair). My problem with this single point things is that I have a 3-level house where I'm doing this, so getting a bunch of wires from all across the house to just 1 point goes into the madness zone in my head. If I think bigger, like a big office building, it creeps me out even more. So I think there is something about this single connection to a common point thing that I am just not getting. Do you have a good reading reference for this? – ciuly May 7 '19 at 20:03


  1. Setup = Many many RPi's, relays, sensors powered by many many [5V, 10A] PSUs

  2. OK to connect all the PSUs together at the Negative [Ground] terminal negative ('-')?

  3. Sufficient for the RPIs controlling relay and sensors?

  4. Still need connect all Rpi's [signal] GNDs to the PSU ground's

  5. Does any "end" of it require any other components to make it safe/safer?

  6. Or better connect the RPis GND's to the actual [mains 200VAC] earth ground?

  7. Difference between [200VAC mains] earth ground and RPI ground pins

  8. Understanding this 1 would probably allow me to answer myself all the previous questions. Maybe.


So you have a long list of questions. Let me start at the end, Q8 + Q7.

Difference between [200VAC mains] earth ground and RPI ground pins

As I understand, all wall warts (except perhaps the very expensive Apple ones) do not ground to the mains ground, because they have insulated plastic covers and would not leak electricity (so as the bubble gum vendor say), though I often heard from news, up north of my city, that some 10 mobile users got killed by electricity leaking fake USB chargers every year. Nowadays it is no loner "news", so I don't hear those news and have lost count now. But I do remember not to long ago Samsung 7 chargers explode. But like all huge SamSung fans, I have a very short memory, and still renewing my Samsung handset every one or two years.

apple charger

Though I don't earth ground my floating PSU, I always ground the casing, as described in the following answer:

How to ground your floating PSU and 200VAC mains output relay modules

relay module grounding

chassis grounding

Does any "end" of it require any other components to make it safe/safer?

It is not clear what do you mean by "safer". Does it mean less EMI floating around and cause your old cat an heart attack? Or safer because EMI won't attack your Rpi and cause it intermittently self reboot? There are 101 ways to make you thing "safer". For the EMI thing, you might like to add a "snubber". See below.

Using Snubbers to suppress EMI


And to play safe, you can use electricity leakage protect circuit breaking plugs.

circuit breaking plugs

RCBO for outdoor 200VAC mains

And if your 200VAC mains extends to outdoor, like my rooftop garden, you may consider installing a 200VAC 10A RCBO for all the relay modules, as show below. I am planning to use DC12V for relays and motors, DC24V for home appliances such as desk lamps. I avoid using relays to control 200VAC for safety reasons. On the other hand 12/24VDC is optimum. DC24V wall warts are common of home desk lamps. One way is to borrow the DC24V to supply the Songle 24V based relay modules (still 5V control signal though). This is a bit complicated. Perhaps I could show more pictures later, ...


Still need connect all Rpi's [signal] GNDs to the PSU ground's?

Well, if you browse the EE StackExchange, the EE guys would tell you that home mains 220VAC grounding is the mother of all noises. In other words, all noise bad guys, no mater back EMF or EMI (actually boils down to the same thing, according to the Scottish guy Maxwell and his huge fan Heaviside)) travels through the connecting wires (or more precisely, on the skin of the wires). So using the relay as an example, I almost never connect Rpi's signal ground to the relay's Songle relay switch 5/12/24VDC power ground. I only communicate/talkrol through light/optical (OK, still electromagnetic waves) signal to the Songle guys. In other words,


relay ground isolation

many many [5V, 10A] PSUs

So we have scratched the surface of the 200VAC mains / 5V DC PSU grounding problem. Now let us jump to the beginning of your quesions list, the 5V, 10A PSUs.

There are many styles of distributing PSUs. I have 4 Rpi3B+, and I have 4 12V in 5V out, 3A+ PSUs, each of which is dedicated to one and only one Rpi. You may like to read my answer to the following post to get a rough idea of how I treated my Rpi like a VIP, with dedicated PSU, private bath rooms, etc,... :)

Dedicated PSU (with 10,000 uF by pass cap) for VIP Rpi

rpi psu

Earth stud example

earth stud example

The relay box has an earth stud where the earth wires of all 6 anodized aluminium plates go to, forming a single earth point. This earth thing is for safety, so that any loosen dangling main live wire touching the chassis will not cause any harm to the human body touching the chassis, because almost all leaking electricity will pass through the earth wire to live wire to plug, to socket, to home mains MCB, and in my case, to the 28 story flats down to the real earth stud buried at the basement of the building (This is what I read and educated guess, I have not seen the real earth stud!) The AC 12V/24V transformers are floating, not touching the metal chassis or the quad relay board.

relay board grounding.

Update 2019may11hkt1212

200VAC Mains Earth vs 6~30VDC PSU Power Ground vs Logic Circuit Signal Ground

I usually distinguish among three earth/grounds by colours and AWG.

  1. Main Earth - Green, thickest (standard 15A mains wire), connected to plug's earth wire, etc

  2. PSU Ground - Black, thick (AWG 22+)

  3. Logic Ground - Grey, thin (AWG 26~30)

I usually use a tree/hierarchical grounding configuration, not a star, never a ring. And PSU ground is never connected to mains earth. I know many industrial/academic labs have their PSU ground connected to main earth to illuminate all mains noise. But I never did that. Perhaps you can google and convenience me that it is a good idea.

psu grounding config

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  • Lot to read :) So on your point 7: I went through it twice but I'm not seeing how the mains/earth grounding is different from the RPi GND pins. I am looking at the PSU of the RPi and there is no earth ground. However I am using a shielded FUTP cable going into the RPi, so does that count as the earth grounding of the RPi and can I assume there is no connection to the RPi GND pins? – ciuly May 7 '19 at 9:57
  • On point 5: by safer I was aiming at the same kind of potential issues as you mentioned in my other SE Q had I went the option of using resistors instead of the 2N2222. Basically, anything I need to be careful enough given that I'm barely starting in these electronics things and would like to avoid frying my equipment ;) Thanks – ciuly May 7 '19 at 10:02
  • Point 4: I am noticing that you rephrased that as connect to PSU ground, and your explanations seem to go that way. However my question was about connecting them all the PSU(s) negative pole. So both points 2 and 4 seem to remain unanswered (And/or I am not properly getting that whole capacitor thing) Thanks – ciuly May 7 '19 at 10:12
  • @ciuly Ah it seems we have a totally confusing mess. Let me try to clarify a little bit, by first "formallising" the use of the technical terms. (1) I usually and often casually say the "metal chassis" of the PSU should be earthed/grounded. Inside the metal chassis, the switched power supply is NOY touching the metal chassis, therefore not earthed/grounded. I need to find a picture to make myself clear. Perhaps tomorrow. :) – tlfong01 May 7 '19 at 12:19
  • @ciuly I have added an earth stud example a the end of my answer. You might like to google earth stud or the follow link to read more details. scame.com/en/General_Catalogue/Earth_stud/5155_0000000001_cat – tlfong01 May 8 '19 at 9:15

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