IEC Symbol Meaning

That's a Varistor symbol, an MOV or SIOV

I wonder if it is a variable resistor symbol to represent the resistance of the winding which would change with temperature. In that case why would they not include the capacitance across the coil as well? Therefore more likely to be a varistor as already stated, this being my HO.

While you are most likely correct that that is a thermistor, the strange application does give rise to some wondering thoughts. I've seen way too many schematics now, where the drafter/designer makes up their own symbols loosely based on ones they've seen before. I think you are definitely right asking for more of the circuit, or a lead sheet, to help decide the answer.

Actually, I don't think I've seen a schematic sent to me in the past 25 years of control work, where the drafter actually followed a guide by any recognized organization be it IEC or IEEE or whomever to perfection. They've all had some personally re-designed symbols requiring a lead sheet or a discussion with the source of the drawing.

I'll give you a GA on this one anyhow.

I think it is a resistor with a positive temperature coefficient (PTC).

The circuit is odd - the transfo does not have an iron core drawn. It is described as a PT, but such would usually have a core to improve its voltage transfer accuracy and very low reactance.

If it were air cored, it would have much higher regulation - in that case, the secondary might be heavily loaded by the resistor initially, to reduce voltage to other loads - increased resistance as it warmed up, some PTC increase very sharply at a certain temperature like those used for winding temperature alarm.

However, shunting the winding, that way, would be strange on a proper VT with very low reactance - it would overload the VT and require a lot of power into the PTC.

It would help if the Hz, VT rating, Voltage in/out, what is connected to PT and purpose of the whole installation were explained. Also part number of PTC!