[SOLVED] earthing and grounding

I am designing a circuit to control heater. with 2 boards. One main board containing the input AC voltage from a troidal and other board with sensor. In the main board the troidal is connected to the main board through 3 wires (supply and return of the AC voltage and the earth(body of the troidal)). On the main board the ground of the DC voltage regulator is connected to the earth. The ground of the sensor board is connected to the ground of the main board. i.e the ground of the 2 boards are connected to each other and the ground of the main board is connected to earth(body of the troidal).
My question is should I connect the earth of the heater directly to the troidal body and connect the sensor board ground separably to the ground of the main board (which is connected to the earth) or I can just remove connection between the two boards and connect the ground of the sensor board to the earth of the heater to the earth of the troidal (it's body which is connected to the ground of the main board)?? Does it make any difference?????

There is a huge Difference Between Grounding and earthing in Electronic circuits. The Earth is a Protection Concept, ie if any leakage occur in electrical things like Heater or something (High voltage high power devices), the Earth Path was a powerful LOw resistance path to Earth ( Ground Potential) to protect the being which handled the device.

But in the case of ground, that is a reference potential, which is all the electronic component,s referance was defined wrt ground potential. in some cases it may not be at 0 (Any interruption occur in this point will directly affect the working of your circuits ).

Never connect a ground Pin to The Body Earth of your device, it may damage your electronic circuits and sensors

Your toroidal transformer, I have never seen an earth on one because the metalwork (core) is totally covered in the windings and insulation tape, i.e. there is no exposed metal to be "earthed". I could see an electrostatic screen being incorporated, to be earthed to reduce inter winding capacitive pick up of mains borne transients. Your heater, this earth is for the metalwork and not the supply return lead?
As said before, if something goes wrong, like the transformer goes short circuit mains live to the low voltage output, you want to make sure that anything you can touch will not become live too, so all exposed metalwork should be connected to a low resistance path to that actual earth. Usually the incoming mains earth is good enough for this purpose.
Supply returns, if you have high current supplies and devices, it is best to run their returns as directly as possible, because there may be voltage drops along these wires that can interfere with sensitive circuits.
Frank

sreepss said:

There is a huge Difference Between Grounding and earthing in Electronic circuits. The Earth is a Protection Concept, ie if any leakage occur in electrical things like Heater or something (High voltage high power devices), the Earth Path was a powerful LOw resistance path to Earth ( Ground Potential) to protect the being which handled the device.

But in the case of ground, that is a reference potential, which is all the electronic component,s referance was defined wrt ground potential. in some cases it may not be at 0 (Any interruption occur in this point will directly affect the working of your circuits ).

Never connect a ground Pin to The Body Earth of your device, it may damage your electronic circuits and sensors

Click to expand...

So it's not right to connect the DC gnd to the main earth, because I thought that will protect the components from any shock or static charges. In other word you mean that the earth is only for protection of the users from electric shocks not to protect the electronic components.

---------- Post added at 12:35 ---------- Previous post was at 12:29 ----------

chuckey said:

Your toroidal transformer, I have never seen an earth on one because the metalwork (core) is totally covered in the windings and insulation tape, i.e. there is no exposed metal to be "earthed". I could see an electrostatic screen being incorporated, to be earthed to reduce inter winding capacitive pick up of mains borne transients. Your heater, this earth is for the metalwork and not the supply return lead?
As said before, if something goes wrong, like the transformer goes short circuit mains live to the low voltage output, you want to make sure that anything you can touch will not become live too, so all exposed metalwork should be connected to a low resistance path to that actual earth. Usually the incoming mains earth is good enough for this purpose.
Supply returns, if you have high current supplies and devices, it is best to run their returns as directly as possible, because there may be voltage drops along these wires that can interfere with sensitive circuits.
Frank

Click to expand...

Actually I mean by the troidal body a metal ring base where the troidal is placed on, and this metal base is connected to the main earth. The main earth is the third wire from the main cable feeding the 220V to the troidal input. sorry for any misunderstanding.

I am fully agree and satisfied with Sreepss answer. you need to take notice of these things.