A current transformer is a device used to produce an alternating current in its secondary , which is proportional to the AC current in its primary. This is primarily used when a current or voltage is too high to measure directly. ... The CT ratio is equal to the number of secondary turns. Specification: Model Ratio(A) Burden(VA) Case Qty.(Pcs) MSQ-40 Class:0.5 Class:1.0 100/5 1.5 1.5 40 150/5 1.5 2.5 40 200/5 2.5 5 40 250/5 5 5 40 300/5 5 5 40 400/5 5 10 40 500/5 5 10 40 Package Includes: 1 x 100amp To 5Amp Current Transformer