Can you share common neutral with different voltage system?

Thread Starter

MacaroniLeader

Joined Apr 15, 2022
4
I have 3 AC to DC transformers powered by same breaker AC breaker:

1. 120ac to 48v dc
2. 120ac to 24v dc
3. 120ac to 12v dc
4. 12v dc to 9v dc step down to power Arduino
5. 5v dc sensor system powered by Arduino board and ground from Arduino board

Is it possible to have one neutral/ground bar to connect all of the above systems without messing up Arduino board electronics and sensor readings?

5v system is used to power displays, relays and reading from various sensors
12v is used to switch solenoids (with 5v relays)
24v is used to drive motor (with 5v relays)
48v is used to drive 24v motor located over 90feet away from Arduino with 48v to 24v step down at the spot

It is not traditional schematics, but it was faster for me to code flowchart in GitHub. Excuse floating + and -.
Screen Shot 2022-04-15 at 9.46.36 AM.png

I would love to use same ground to simplify wiring and save on wires.

Any response or input is appreciated.
Thank you!
 

Thread Starter

MacaroniLeader

Joined Apr 15, 2022
4
As long as the AC side is isolated from each other, you can common up the DC commons.
Called equi-potential bonding.
Thank you for your reply, I found online definition of equipotential bonding:

Equipotential bonding (EPB) is the process of electrically connecting metalwork and conductive parts, both exposed and extraneous, such that the voltage is the same throughout these various parts. EPB is used to reduce the risk of equipment damage and personal injury.

It says something about the same voltage.
Yes, DC and AC are isolated.
Are you sure it would not mess up electronics such as 5v Arduino?
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
I presume you have isolation devices between the Arduino and the relays etc?
It is common in many industrial systems to earth bond the commons , generally a Star point ground is set up to terminate all the grounds, It is also usual to connect the service earth GND conductor to this point.
Your desk top or tower PC internal L.V. P.S. is usually connected to the earth GND also via the MB fixing screws to case.
 

Thread Starter

MacaroniLeader

Joined Apr 15, 2022
4
I presume you have isolation devices between the Arduino and the relays etc?
It is common in many industrial systems to earth bond the commons , generally a Star point ground is set up to terminate all the grounds, It is also usual to connect the service earth GND conductor to this point.
Your desk top or tower PC internal L.V. P.S. is usually connected to the earth GND also via the MB fixing screws to case.
I have not acquired all parts yet. For relays, I have two options. As far as my minimal electronics understating goes, I assume they are both isolated.

A: (5v version)
713KT1PwrhL._SL1500_.jpg
B: (Opto-Isolated Relays, 12v but I read I could still use 5v Arduino output pin to start the relay)
819w3pa9OsL._AC_SL1500_.jpg
Would you say they are both OK?

By saying "...it is also usual to connect the service to GND conductor to this point." - do you mean I should also connect my common (DC) to ground wire (AC) of the home electrical system? Such as ground on 120V outlet. It is bonded to neutral in the breaker box but also connected to the ground spike.

In this case I can connect ground to the metal housing and bond both AC ground and DC common to it. This leads me to think I can use ground of AC wiring for common of sensors and solenoids that are located further away from Arduino?

Thank you again for your input!
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
Although you are using the earth ground symbol for all the 'Ground' connections, I assume they are all common.
In industrial systems, it is quite common to set up a star point earth GND where all systems are referenced to.
You cannot bond all AC and DC commons without first establishing that they are initially isolated from one another.
For e.g. if you have a number of different isolated circuits, the commons of each can be connected to a common earth star point together with the service GND by choice.
Another example is if the AC feeding a power supply is at earth GND, you cannot earth GND any resultant DC derived from this AC unless each is totally isolated from each other.
 

Thread Starter

MacaroniLeader

Joined Apr 15, 2022
4
Although you are using the earth ground symbol for all the 'Ground' connections, I assume they are all common.
Yeah, common (GND). You are thinking of me too highly, this is the schematic I downloaded from the relay manufacturer. :)
In industrial systems, it is quite common to set up a star point earth GND where all systems are referenced to.
Star point earth is basically ground bus bar that grounds all power supplies, electronic components and relays in the enclosure?
You cannot bond all AC and DC commons without first establishing that they are initially isolated from one another.
For e.g. if you have a number of different isolated circuits, the commons of each can be connected to a common earth star point together with the service GND by choice.
Another example is if the AC feeding a power supply is at earth GND, you cannot earth GND any resultant DC derived from this AC unless each is totally isolated from each other.
As I understand all different DC volt systems of the enclosure connected to eacantonly with one common (GND) to a bus bar - makes them isolated and at the same time by connecting only with one wire from each also bonds them?

With second example if I would connect earth of AC that is feeding in power converters (however it is only powered by live and neutral) in the enclosure to a GND of DC that is fed by said power converters it could damage or interfere with the system? Unless I first connect GND of volt systems to a bus bar and connect earth of AC to said ground bar?
Or I should have ground bus bar for each volt system and then connect each of them to a ground bar of AC?
 

MaxHeadRoom

Joined Jul 18, 2013
25,469
If I understand the question, you can bond the star ground of the DC commons as shown in post #1 to the service earth GND, as long as any power supply producing the DC does not have any reference to said GND at any other point involved in producing or creating the DC .
 

dendad

Joined Feb 20, 2016
4,170
On your opto isolated relay circuit, add a pull down resistor from the base o emitter of each transistor. It is good practice to not allow "undefined" conditions to arise, like a floating base of a transistor.
But you hardly need the optos if relays are used. The relays provide the isolation.
In my industrial control equipment, the 24V is usually grounded on the -Ve side but the 5V is floating, and optos and relays provide the 5V to 24V isolation.
 
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