Earthing vs grounding

[mohamed.elsabagh]

I tried to ask this question for long time but I didn't get a real answer, should I connect my digital ground to the common earth or not?? (third wire from the power socket)

 

[andre_luis]

This is not safe to customer, because depend on proper grounding of socket were system will be plugged.


+++

 

[mrarslanahmed]

no..... not safe....... main reason

i think ground is meant for dc while earth meant for ac....

correct me if i am wrong.

 

[mohamed.elsabagh]

no..... not safe....... main reason

i think ground is meant for dc while earth meant for ac....

correct me if i am wrong.

actually I am not sure, but as far as I know the earth terminal is connected to the real earth (soil) using special technique, in this case this terminal will be of very very low resistance so most of the current will flow through this terminal if a man touches the case which is earthed. In this case the man will be safe because when the current flows through the less resistance terminal a large ampere flows through this terminal and the circuit breaker should break.
For the ground, it should be arbitrary point where I measure all the voltages of the circuit with respect to it.

 

[kak111]

Maybe this picture gives some ideas.....

Auxliary EARTH usually wired to earth wire in power grid

 

[HTA]

The third connection on the power plug is defined as the protective ground, which is connected only with the case. AC current should flow only thorough the P to N line. In case there is a failure and current flowing from P or N line to the protective ground(e.g. due to an isolation problem or a short) the central power distribution box (e.g. in a house or factory) is detecting this failure current (typically 50mA or less) and disconnect the power line. Thus the protective ground is making sure that there is not dangerous AC voltage on case parts human can touch and cause death or massive damage to the user. The protective ground is only once connected to an earth grounding. Thus a DC power distribution should not connect the protective ground to DC ground. If the third line is defined as a normal ground then it can be connected. The best is to check with the utility how the third line is used/defined.

 

[mohamed.elsabagh]

The third connection on the power plug is defined as the protective ground, which is connected only with the case. AC current should flow only thorough the P to N line. In case there is a failure and current flowing from P or N line to the protective ground(e.g. due to an isolation problem or a short) the central power distribution box (e.g. in a house or factory) is detecting this failure current (typically 50mA or less) and disconnect the power line. Thus the protective ground is making sure that there is not dangerous AC voltage on case parts human can touch and cause death or massive damage to the user. The protective ground is only once connected to an earth grounding. Thus a DC power distribution should not connect the protective ground to DC ground. If the third line is defined as a normal ground then it can be connected. The best is to check with the utility how the third line is used/defined.

impressive, Thanks so much but I am designing a device which is going to sell all over the world, what should I do if it differs from one place to another??

 

[andre_luis]

I think the main question is : What is the project requirement that convinced you to connect them ?


+++

 

[mohamed.elsabagh]

I think the main question is : What is the project requirement that convinced you to connect them ?


+++

Nothing at all but someone told me it would be safer for the component, he also told me that the microcontroller could hang if I didn't connect the earth and the ground, I though he was wrong because of the above reasons but I didn't find anything useful on the internet, but I am more convinced to disconnect the earth and the ground now.

 

[andre_luis]

mohamed,


I agree with you on that conclusion.

However, he could be talking about some particular circuit topology in wich this statement could be true.
Could provide the schematic diagram in that you are working, to eliminate some remaining doubt ?


+++

 

[abaz]

What about the ground lead being connected to the earth pin on osciloscopes ?

 

[HTA]

The cable shields could be connected to the earth potential. Connecting ground to earth is not recommended if it is a protective earth. It is possible to get ground loops if there are several different AC line connections(e.g. measuring on another equipment with an osciloscope). Then it is better to have a floating ground.

 

[mohamed.elsabagh]

mohamed,


I agree with you on that conclusion.

However, he could be talking about some particular circuit topology in wich this statement could be true.
Could provide the schematic diagram in that you are working, to eliminate some remaining doubt ?


+++

Actually he is the one who have the schematic :smile:, I don't have it but he himself is not sure of what are we arguing about so I am sure he is not talking about particular circuit topology. Any way if I can get the schematic from him I will provide you with it to give me your opinion. Thanks bro.

 

[Syncopator]

I tried to ask this question for long time but I didn't get a real answer, should I connect my digital ground to the common earth or not?? (third wire from the power socket)

There is widespread misunderstanding of the the word "ground".

The meaning of "earthing" should be obvious from the word itself.

"Grounding" however, is a different matter entirely. What it means is usually dictated by what the user thinks it means, and this is often wrong, not say dangerous.

For now, take "grounding" to mean a common connection for all parts or sections of a circuit, usually the common, or 0V, of the power supply/supplies.

Analogue and digital parts of a circuit will often have separate "ground" connections which are ultimately connected together at one point.

In mains operated equipment it is usual, unless it is double insulated, to have the circuit ground connected to the earth pin of the supply. This may be to prevent mains hum in the case of audio equipment.

If your equipment is not double insulated it would be prudent to make that connection too. One option, which is provided my some manufacturers, is to provide an external link which may be connected or disconnected at the discretion of the user.

 

[mohamed.elsabagh]

There is widespread misunderstanding of the the word "ground".

The meaning of "earthing" should be obvious from the word itself.

"Grounding" however, is a different matter entirely. What it means is usually dictated by what the user thinks it means, and this is often wrong, not say dangerous.

For now, take "grounding" to mean a common connection for all parts or sections of a circuit, usually the common, or 0V, of the power supply/supplies.

Analogue and digital parts of a circuit will often have separate "ground" connections which are ultimately connected together at one point.

In mains operated equipment it is usual, unless it is double insulated, to have the circuit ground connected to the earth pin of the supply. This may be to prevent mains hum in the case of audio equipment.

If your equipment is not double insulated it would be prudent to make that connection too. One option, which is provided my some manufacturers, is to provide an external link which may be connected or disconnected at the discretion of the user.

First of all thank you for your reply, but now I am confused again :-?. The circuit I am talking about consists of power module which provides DC voltage from the input 24AC voltage on the toroidal output. I have also microcontroller, LED, zero crossing, couple of opamps from a sensor,... .The microcontroller controls a heater through a MOSFET switch where the input supply of the heater is the 24AC. The heater it self has an earth return wire which I am going to connect to the earth of course. The main problem here do I need to connect the earth to the ground (which is the ground of the DC voltage regulator, and the ground of all digital modules including the microcontroller). I think I don't have to connect this connection, no I think it's not wise to do that am I right???. I asked my friend for the schematic but he told me it's not ready yet maybe when it's ready I would share it here to have a final look.

 

[Syncopator]

The main problem here do I need to connect the earth to the ground (which is the ground of the DC voltage regulator, and the ground of all digital modules including the microcontroller). I think I don't have to connect this connection, no I think it's not wise to do that am I right?

I think it better to make that connection, i.e. a connection between your circuit grounds and the earth.

If you do acquire the circuit it would be interesting, and perhaps helpful, to see it.

 

[mohamed.elsabagh]

Ok but let's say a spark is generated which should flow through the earth connection, won't this affect the ground and subsequently the whole voltage in the circuit which could be dangerous for the components?? and again what is the role of the protective earth, isn't it to protect the human working with the machine not to protect the component, where in the case of protecting the component there should be ESD safety procedure??What do you think?

 

[Syncopator]

It is impossible to hypothesise about the cause or results of a spark.

However, so long as the case, or anything conductive mounted on the case, is connected to earth, then there is no necessity to connect the circuit's ground/s to it.
But it is usual to do so. The choice is yours.

 

[mohamed.elsabagh]

It is impossible to hypothesise about the cause or results of a spark.

However, so long as the case, or anything conductive mounted on the case, is connected to earth, then there is no necessity to connect the circuit's ground/s to it.
But it is usual to do so. The choice is yours.

Ok great I agree but what are the basis I should take care of when I choose??? Is it different between analog and digital ground???

 

[Syncopator]

I'm sorry, but I can't make that decision for you.