Current transformers and ammeters go together. Current transformers gather the data but lack the equipment to show it, which is why they need to be hooked up to an ammeter. Like the voltmeter and ohmmeter, the ammeter measures the amperage or current flowing in a circuit and displays the data in amperes.
Amperage not only gives you an idea of the current in the load but also how much is too much. Without the right load to slow it down, the excess current will generate heat, making the entire circuit short out. In addition, loads must have the right resistor to help slow the current down, especially with electronics growing more delicate.
For this reason, current transformers and ammeters should never be used without the circuit connected to a load. Ammeters are usually protected from short circuits, but they won’t be able to operate unless the fuse—which blows up in such a scenario—can be replaced.
To mitigate a potential short circuit, the line can be wound around the current transformer. Apart from measuring current, current transformers are also in the business of stepping down current, similar to a voltage transformer. A wire with a current ratio of 300:5 can have its primary current (300 A) halved by a secondary winding.