Is ground physically 0V or just a reference (like maybe 2.5V) that we use to measure voltages from?

Should i be grounding the VSINE or just take the voltage across it without the reference. Basically i have understood the connected ground is not actually 0V, but only a reference point, because only that would explain the voltage being same in both the circuits across the VSINE component.

Without the ground on the VSINE, i can see that the voltage shown by the probes is same in magnitude but opposite in polarity, for example in the screenshot, -2.8V and +2.8V, which would give a Voltage difference of -5.6V, basically a point on the negative half cycle.

The same can be said of the circuit with the ground, now that i have made one terminal the ground (reference?).

What reference voltage is the probe taking in both the circuits?

Is all this thinking in the right direction?

 

Is ground physically 0V or just a reference (like maybe 2.5V) that we use to measure voltages from?

Should i be grounding the VSINE or just take the voltage across it without the reference. Basically i have understood the connected ground is not actually 0V, but only a reference point, because only that would explain the voltage being same in both the circuits across the VSINE component.

Without the ground on the VSINE, i can see that the voltage shown by the probes is same in magnitude but opposite in polarity, for example in the screenshot, -2.8V and +2.8V, which would give a Voltage difference of -5.6V, basically a point on the negative half cycle.

The same can be said of the circuit with the ground, now that i have made one terminal the ground (reference?).

What reference voltage is the probe taking in both the circuits?

Is all this thinking in the right direction?

0V is your reference point from which all measurements are made.
Yes, for simulation purposes you should ground (i.e make your COMMON reference point) one side of the AC source.

If your AC source is LIVE AC MAINS, as in real life house wiring, NEVER ground any of the AC LIVE or NEUTRAL lines.

 

An exemption which is optional, is when you use a transformer which results in galvanic isolation from any AC supply that has a neutral that is earth grounded.
It is permitted to re-establish a grounded neutral by taking one of the secondary conductors to the earth ground conductor, from There on these two conductors are treated as a normal Earth and Neutral conductor.
In a DC circuit that is derived from an isolated transformer secondary , the DC common is permitted to be connected to earth ground.
But not both AC secondary AND DC common.
Max.

 

Just to confuse things a bit, here in Australia, the neutral on the mains power (240V) is connected to the mains earth at the switchboard where the mains enters the building.
But you never connect the neutral to the earth anywhere else. In fact, if you do, the earth leackage protection circuit will operate and drop the power off. There is a core balance relay that must have the active and neutral currents the same so they cancel out for the power to remain on. At least in all new buildings, and if any electrical work is done on old buildings, the power board must be updated to to inclued this feature.
An isolation transformer is a great tool to have and I recommend getting one, or you can use a couple of identical transformers back to back to make your own. My first isolation transformer was made like that from a couple of transformers from old black and white TV sets.

 

An exemption which is optional, is when you use a transformer which results in galvanic isolation from any AC supply that has a neutral that is earth grounded.
It is permitted to re-establish a grounded neutral by taking one of the secondary conductors to the earth ground conductor, from There on these two conductors are treated as a normal Earth and Neutral conductor.
In a DC circuit that is derived from an isolated transformer secondary , the DC common is permitted to be connected to earth ground.
But not both AC secondary AND DC common.
Max.

Hi MAX, as you mentioned the DC ground and AC secondary must not be connected, well i measured the voltage difference between them and this confirmed the fact the "ground" is just a reference. But if the earth ground and the neutral are connected together in a mains distribution system, won't there be a current (pretty must alternating current) between these two lines, just to keep them both at the same potential? It does not make sense because the N and E are connected together and if the earth is at 0V, then shouldn't N also be at 0V? If the N and E are connected together, the technically, isn't the voltage reference floating because of the nature of AC (see V1's circuit and how the voltages are equal but opposite in direction)?

 

If your AC source is LIVE AC MAINS, as in real life house wiring, NEVER ground any of the AC LIVE or NEUTRAL lines.

In the U.K the neutral and earth are bonded together at the consumer supply meter!

 

I just measured 240V AC between N and E lines using a fluke multimeter (17B). Am i seeing things or should this value be 0V?

 

Is ground physically 0V or just a reference (like maybe 2.5V) that we use to measure voltages from?

Should i be grounding the VSINE or just take the voltage across it without the reference. Basically i have understood the connected ground is not actually 0V, but only a reference point, because only that would explain the voltage being same in both the circuits across the VSINE component.

Without the ground on the VSINE, i can see that the voltage shown by the probes is same in magnitude but opposite in polarity, for example in the screenshot, -2.8V and +2.8V, which would give a Voltage difference of -5.6V, basically a point on the negative half cycle.

The same can be said of the circuit with the ground, now that i have made one terminal the ground (reference?).

What reference voltage is the probe taking in both the circuits?

Is all this thinking in the right direction?

You are lucky your simulation even ran since your top part of the circuit has floating nodes. Sometimes you get lucky. A lot depends on the netlister and the simulation engine.

The concept of something being "physically 0 V" is without meaning. In any circuit, you get to arbitrarily define the voltage on one node to be anything you want. By widely used convention, we pick a reasonable node ("reasonable" for the context of our purposes) and declare it's voltage to be 0 V. This is critical because the simulator keeps track of node voltages and not voltage differentials. The very notion of the voltage on a node is meaningless without a reference node to which it is referred.

In most simulators, the engine needs a defined 0 V node and this is usually the node named "0". In the schematics, this is usually defined using a "ground" symbol. But you can also just name the node "0" and it will work just as well as long as it is a global name (at least in all the schematic capture packages I've used).

 

Hi MAX, as you mentioned the DC ground and AC secondary must not be connected, well i measured the voltage difference between them and this confirmed the fact the "ground" is just a reference. But if the earth ground and the neutral are connected together in a mains distribution system, won't there be a current (pretty must alternating current) between these two lines, just to keep them both at the same potential? It does not make sense because the N and E are connected together and if the earth is at 0V, then shouldn't N also be at 0V? If the N and E are connected together, the technically, isn't the voltage reference floating because of the nature of AC (see V1's circuit and how the voltages are equal but opposite in direction)?

In most systems, the AC neutral is physically bonded to physical ground at the service entry point (and, in many systems, also at the secondary of the distribution transformer providing the service).

Under non-fault conditions, virtually no current flows in the safety ground because it has a much better path back to the transformer via the wiring. However, because the neutral wiring in the structure has resistance and there is current flowing in it, then there is a small voltage difference between the neutral and the ground wire at various places throughout the structure that depends on the current being drawn in the various circuits. As a result, if the neutral gets shorted to the ground wire at places other than the service entrance, it is likely that some current will flow in each. This is where GFI circuits come into play because if they sense any difference (beyond a few milliamps) between the hot and the neutral wires, they trip.

 

In most systems, the AC neutral is physically bonded to physical ground at the service entry point (and, in many systems, also at the secondary of the distribution transformer providing the service).

Under non-fault conditions, virtually no current flows in the safety ground because it has a much better path back to the transformer via the wiring. However, because the neutral wiring in the structure has resistance and there is current flowing in it, then there is a small voltage difference between the neutral and the ground wire at various places throughout the structure that depends on the current being drawn in the various circuits. As a result, if the neutral gets shorted to the ground wire at places other than the service entrance, it is likely that some current will flow in each. This is where GFI circuits come into play because if they sense any difference (beyond a few milliamps) between the hot and the neutral wires, they trip.

So, the Neutral wire is actually one of the terminals of the secondary side of the step down transformer, right?

 

So, the Neutral wire is actually one of the terminals of the secondary side of the step down transformer, right?

How did you arrive at that conclusion?

In a properly designed, built, and working transformer, the secondary windings are galvanically isolated from the primary windings. There is no electrical connection between the secondary side and the live and neutral wires on the primary side.

That is the reason it can be used as an isolation transformer.

 

In most systems, the AC neutral is physically bonded to physical ground at the service entry point (and, in many systems, also at the secondary of the distribution transformer providing the service).

Under non-fault conditions, virtually no current flows in the safety ground because it has a much better path back to the transformer via the wiring. However, because the neutral wiring in the structure has resistance and there is current flowing in it, then there is a small voltage difference between the neutral and the ground wire at various places throughout the structure that depends on the current being drawn in the various circuits. As a result, if the neutral gets shorted to the ground wire at places other than the service entrance, it is likely that some current will flow in each. This is where GFI circuits come into play because if they sense any difference (beyond a few milliamps) between the hot and the neutral wires, they trip.

Then why does the top part of the circuit display node voltages? What is the reference for these voltages?

Since the voltage between L and N must be 230V, it could mean that L and N can be 1230V and 1000V separately. Then connecting N to E in this case will lead to a current that will need to f

You are lucky your simulation even ran since your top part of the circuit has floating nodes. Sometimes you get lucky. A lot depends on the netlister and the simulation engine.

The concept of something being "physically 0 V" is without meaning. In any circuit, you get to arbitrarily define the voltage on one node to be anything you want. By widely used convention, we pick a reasonable node ("reasonable" for the context of our purposes) and declare it's voltage to be 0 V. This is critical because the simulator keeps track of node voltages and not voltage differentials. The very notion of the voltage on a node is meaningless without a reference node to which it is referred.

In most simulators, the engine needs a defined 0 V node and this is usually the node named "0". In the schematics, this is usually defined using a "ground" symbol. But you can also just name the node "0" and it will work just as well as long as it is a global name (at least in all the schematic capture packages I've used).

 

Are you referring to a simulation or are you measuring real voltages on AC mains wiring?

If there is 240VAC between N and E wires then there is a serious problem with your house wiring.
This calls for immediate investigation by an experience and licensed electrician.

 

I did not mean that the secondary and primary are electrically connected. The whole point of AC is that the voltage between the L and N is 230V, right? Then, we don't know what potential the N wire is at or for that matter the L, all that is required is that the Potential difference between them is 230V.

I'm just really confused, especially after seeing the top part of the circuit in simulation showing a voltage (not potential) at 2 different nodes, without a reference! How is that possible?

 

You are absolutely right! And fortunately (or tragically?) this is the situation at my workplace. After further investigation i found out that the electricians in India, often interchange the L and N connections from the distribution box to the socket! Can you believe that?! I verified this because the L socket to E is 1.45V and N socket to E is 240V.

This is with reference to the wall sockets, not the simulations

 

I did not mean that the secondary and primary are electrically connected. The whole point of AC is that the voltage between the L and N is 230V, right? Then, we don't know what potential the N wire is at or for that matter the L, all that is required is that the Potential difference between them is 230V.

I'm just really confused, especially after seeing the top part of the circuit in simulation showing a voltage (not potential) at 2 different nodes, without a reference! How is that possible?

It depends on who wrote the code for the simulator and how they treat a simulation of AC mains.

In real life, N wire should be at E potential if the two are properly bonded at the service panel.

 

I'm using the Proteus ISIS simulator here. So technically, the first circuit should have flagged the error that there was no reference, right?

 

You are absolutely right! And fortunately (or tragically?) this is the situation at my workplace. After further investigation i found out that the electricians in India, often interchange the L and N connections from the distribution box to the socket! Can you believe that?! I verified this because the L socket to E is 1.45V and N socket to E is 240V.

This is with reference to the wall sockets, not the simulations

Licensed electricians often do strange and illegal things.

In my house when I moved in, there was a short between N and E behind one of the outlets. The electrician who installed the wiring "fixed" the problem by cutting the E wire on the GFI on the service panel.

 

How did you arrive at that conclusion?

In a properly designed, built, and working transformer, the secondary windings are galvanically isolated from the primary windings. There is no electrical connection between the secondary side and the live and neutral wires on the primary side.

That is the reason it can be used as an isolation transformer.

Sorry, I was referring to a transformer on the consumer side of AC mains.
I now understand that you were referring to the distribution transformer from the power utility company.

Impact of Floating Neutral in Power Distribution

 

It is pointless measuring N to Earth GND with a high impedance meter, if you suspect a voltage between them, test with a load, e.g. incandescent lamp etc.
If the result is no light, then measure the voltage again with the meter in both scenarios, no load and with load.
Max.