Most traditional regular CTs have a 5 ampere as its output, thus most energy meter manufacturers make 5 ampere input meters to match these CT types. Most meter manufacturer themselves do not make the CTs. However this has several disadvantages.
- Most traditional CTs are big and cannot fit into existing panels
When an existing panel needs to be retrofitted with CTs, regular CTs cannot be used because they are too large to fit within the tight spaces between the wiring; thus, to accommodate regular CTs, the load wire needs to be extended and drawn out of the panel to a new panel just for installing the meters and the CTs.
This method is possible, but it is labor intensive and expensive, not to mention that job is complicated and the power needs to be interrupted during installation and would take a long time. Which would most definitely disrupt the work of the electricity user. Then there is the problem of finding space for the new panel, which may not even be possible. Even the aesthetics of the space is made more unappealing.
Thus the need for the dedicated CT.
As a result of the dedicated CT being small, they can be easily installed within an existing panel without the need to change any of the existing wiring or having new panels installed for them, the job becomes much simpler and the installation costs are greatly reduced.
- Regular CTs are only suited for large amperage currents.
Regular CTs are more suited for amperages of 200 or greater. But the large majority of branch circuits will often have amperages that is less than 100 and greater than 20, which are much less than the typical 200 amps found in feeder circuits. Thus, when regular CTs are used to measure such small currents, the load wire needs to be looped through them several times. Otherwise the meter will give grossly inaccurate results.
- A load circuit only has 50 amperes, but a 200 ampere CT is used, 4 loops are needed.
- The same CT as above with a 20 ampere load, 10 loops are needed.
In contrast, with a dedicated CT, not only are they physically small, they are sensitive enough to be able to measure minute current differences. Thus they don’t need looping and the load wire can be passed through directly through the CT once.
- Regular CTs have poor accuracy.
There are of course highly accurate regular CTs, such as those with class 0.5 or even class 0.2, but their price are prohibitively high and are often cost several times that of an ordinary CT. Whereas dedicated CTs are ordinarily found with a class 0.3 accuracy, and are only a fraction of the price.