SCT-013-000 100A Non-invasive AC sensor Split Core Type i.e. it is a current transformer which can be used to measure AC up to 100 amperes. It has no internal burden resistor, but a transient voltage suppressor limits the output voltage in the event of accidental disconnection from the burden. Current transformers (CTs) are sensors are for measuring alternating current. They are particularly useful for measuring whole building electricity consumption (or generation for that matter). The split-core type such as the SCT-013-000 CT in the picture is particularly suitable for DIY use. Clip this SCT 013 000 straight onto either the live or neutral wire coming into the building without having to do any high voltage electrical work.Like any other transformer, a current transformer has a primary winding, a magnetic core, and a secondary winding. In the case of whole building monitoring the primary is the life or the neutral wire (not both) coming into the building itself and going through the hole in the CT. The secondary winding comprises many turns of fine wire housed within the casing of the transformer.