The CT4 is a robust clip-on high current transformer that extends the measurement capability of the P6021, A6302/XL, A6302, A6312 and TCP202 clip-on current probes. Maximum low frequency performance down to 0.5 Hz is obtained using the AM 503S. Current amplitudes to 20,000 A may be measured using the A6302/XL, P6021, A6302, A6312 or TCP202 (with passive termination), provided the amp*second ratings are not exceeded. The CT4 may be used with the P6021 for measurements at normal line frequency and above. (The P6022 and A6303 are not compatible with the CT4.) The CT4 has receptacles for current probes in either 20:1 or 1000:1 step-down ratios. The 1.5 in. square split-core opening makes it possible to clip onto large conductors without breaking the circuit under test. Insulated core and shield assemblies allow measurements on bare wires to 3000 VP (1000 VRMS CAT III) and to 14 kV with the included high voltage bushing.