This CT’s ratio of 3000:1 indicates that it will step down primary current by 3000 times. For example, if primary has 3000 Amps current, the secondary will have 1 Amps.
In case of 5 amp AC signal at input, the transformer will step it down to 1.667 milliamps AC. Where 5/3000 = 1.667 × 10-3 = 1.667 mA
The figure below displays a tiny CT designed for low current measurements, clipped over a wire carrying only a few amps of current. This particular current transformer is constructed in such a way that it may be clipped around an existing wire for temporary test purposes, rather than being a solid toroid where the conductor must be threaded through it for a more permanent installation:
Text and Images extracted from Current Transformer Article by Tony R. Kuphaldt’s Lessons in Industrial Instrumentation, download complete article here in PDF or continue reading online about Current Transformers here.