# Should one terminal of the AC source be grounded?

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 must connect both terminals to your circuit, obviously.

If it's a "floating source" (as these simulation sources, and some - but not all - real sources are), then neither terminal needs to be connected to ground.

AC mains is not a "floating source" as Neutral is connected to ground somewhere (at the substation, if you're in the UK). However, AC mains connected from the secondary of an isolating transformer is a "floating source".

Now, both for simulation and real life, it is usually necessary that there is some path between at least one terminal of the AC source, via some impedance, to ground.

In simulation, that impedance can be high - a nominal 1 Gigohm may do - to establish the initial voltage conditions and allow simulation to converge. Or the connection may be provided by a pair of resistors, connected to 0V and +5VDC, to establish 2.5V DC bias. Or some other approach.

In real life, there will be a similar connection - often via a TVS - to prevent static electricity building up on the otherwise "isolated" circuit, which could otherwise damage the insulation on the isolating transformer.

• Doesn't that mean that there has to be some amount of current flowing between all these points to the main reference point(or ground?). is that why the neutral is connected to the ground, but not necessarily at 0V? It may make more sense if i asked the same question if i replaced the VSINE with the secondary winding of a transformer? Am i right? Then, the reference point throughout the circuit will be what ever potential the secondary winding. But won't reference point itself be alternating, because of the nature of AC/sine? – Prithvi Raj Prakash Aug 4 '17 at 14:16