The difference between the “donut” and “split-core” style CTs is the method required for installation.
The installation procedure is different for “donut” and “split-core” style CTs. A depiction is shown for each (below).
Notice that the installation of the “split-core” style CT doesn’t require any wire disconnection. Although the installation is simpler and quicker that donut CTs, the split-core CTs are more expensive.
The “donut” style CT requires the branch circuit wire to be disconnected in order to thread it through the center of the CT. Although it requires more labor for installation, the donut CT is lower cost and takes less space in the panel.
CT installation inside the electrical panel must be done by a qualified individual or electrician. This individual must be knowledgeable and obey all safety procedures and local electrical code. See users manual for more safety information.