Electronic – Does a current clamp measure apparent or active current? And is it accurate

No, you cannot use a clamp meter on both the live and neutral wires at the same time. Current flowing back through the neutral wire will effectively cancel out current flowing through the live wire, and it will read 0 amps (assuming no current is leaking out anywhere).

One clamp around the live wire should give you the reading you want.

I don't know why you would need 3 clamps though, unless you have 3 phase coming into your building, in which case you'll need to sum the 3 separate currents to get the total current used.

Solution summary:

• APPEARS likely to allow 6 ohms max across output with 3V max out at 50 A in.

• Use 2W+ resistor

• NEVER use with secondary open circuit.

• Use only one wire of circuit through core (active or neutral OK).

• Sensitivity can be increased by a factor of N by looping wire through core N times.

I almost agree with Mike with one important difference.
The transformer appears to be 50A to 5A rated or 50 A to 0.5A rated (see below) but with ANY resistor across the secondary up to 1.5 VA, which is 0.06 ohm. Voltage will then be V=IR = 5 x 0.06 = 0.3V as Mike says.

This seems very strange, as the turns ratio is far lower than usual and the output current much higher.

It seems more likely that the 1A/5A are certification currents and that the ratio is 100:1 as suggested by "Ith = 100 x In" on the label.

Then:
50A / 100 = 0.5A out at 50 A in Vout max = 1.5/I = 1.5/.5 = 3V
Power = I^2.R so R= P/i^2 = 1.5/.5^2 = 6R
Sanity check: I^2R=1/4 x 6 = 1.5VA.

Vmax allowed if the above is correct is 3V at 50 A. You can increase sensitivity by passing the same wire through the core several times. but you can not nominally produce more than 3V.

There are many references to this transformer on web but none seems to give additional information. eg here