These current transformers have a built-in precision resistor that makes the output safe to work with even in a live circuit. The output at the CT’s rating current is 0.333VAC.
The CT’s are available in many current ratings and physical sizes. Please make sure you detemine the correct size for your application. Typically the CT rating should be as close as possible to the max expected current in the circuit measured. This will give the highest accuracy and precision.
There are four basic types of CT’s:
This type of CT is recommended for new, permanent installations. They can not be removed without disconnecting the conductor. They provide high accuracy and are the least sensitive to dirt, corrosion and aging.
Solid core CT’s are available with inner diameters from 7.6mm (0.3″) to 31mm (1.25″) and with current ratings from 5A to 400A.
A split core CT can be opened, mounted around a conductor and closed without breaking the circuit. This is obviously convenient in any installations with existing wiring. There are high accuracy split core CT’s with similar performance as solid core.
Split core CT’s are available with inner diameters from 7.6mm (0.3″) to 31mm (1.25″) and with current ratings from 5A to 400A. High accuracy models are available that meets IEEE C57.13 class 1.2 or class 0.6.
This type of CT is essentially the same as a split core, but bus bar CT’s have a very large opening so they can be mounted around very large conductors – all the way up to 300 by 600mm (24″ x 12″) is possible.
Bus bar CT’s are available with openings from 38x88mm (1.5×3.5″) to 101x114mm (4.0×4.5″). Larger models are special order. Current ratings from 600A to 6000A are available.
Rogowski Coils (a.k.a. Flex CT’s) are a special type of CT that is flexible. They are perfect for large bus bars or irregular shaped conductors. They are typically rated for higher currents, 1000 to 6000A, and require a signal conditioner.
RoCoils are available from 78mm (3.1″) long rated 1000A to 300mm (12″) long rated 6000A.