Maker's Name: 
A J William Electrical Instruments Melb
Where made: 
23 × 8.8 × 26 cm

This unit can either be

Connected in series with a cable carrying AC, using an inbuilt transformer with a number of taps on the primary winding, or

A cable carrying AC can be passed thru the hole in the unit. This provides an alternative primary winding for the transformer

A 5 Amp FSD AC ammeter is connected to terminals L and M, the secondary winding. The meter scale is calibrated to suit the ratio of primary to secondary windings.

The ammeter then shows the AC current flowing in the cable.

The unit is designed to cater for a meter FSD corresponding to 10, 25, 50, 100 Amps serial connection or 200, 400 or 800 Amps AC with 1, 2, 4 loops thru the hole.