Nobody buys a CT by ratio. They buy it for a cabinet, a busbar or a cable that is already there. Five installations cover most of what ships, and each one has a model and one thing that goes wrong.
A feeder needs metering, but production runs three shifts. The CT opens, goes around the live conductor and closes. No busbar removed, no shutdown — that is what this family was designed for.
K-Φ36
· Ø33 mm · 100–600 A
What goes wrong: once the panel is closed, nobody can see whether the CT is still latched. K-SW carries a contact that reports open or closed to the meter — worth it on a twenty-point job where the installer leaves before commissioning.
Scene 02 / Multi-circuit cabinet
You are not running twenty-four pairs of 5 A leads back to a panel door. These cabinets use mA CTs on the outgoing ways and one
multi-circuit meter
reading all of them.
What goes wrong: mA CTs only work on a meter with an mA input. On a 5 A meter they read near zero. This is the wrong shipment we see most often.
The window has to take the bundle, not one bar.
K-120×60
· 62 × 122 mm · 400–4000 A · 0.5 to 2000 A
What goes wrong: the model name is the busbar it was designed around, not the opening. K-120×60 opens to 62 × 122 mm, and the design case is one to three bars per phase. Count the bars before you quote.
A measuring CT saturates at a few times rated current. The relay never sees the fault it was installed to catch.
K-P-120×60
· 5P10 · 300–3000 A
What goes wrong: 5P10 is not a billing class. Protection CTs do not go on a revenue meter, and measuring CTs do not go on a
protection relay
.
The inverter pushes out through the day and the site draws at night. Same cable, same CT — only the meter has to know which way the energy went.
K-Φ50
· Ø48 mm · 500–1000 A · 0.5
What goes wrong: the CT is not directional. Direction is decided by the
meter
, so there is no such thing as a bidirectional CT — buy the bidirectional meter.
measure the cable or busbar, add 5 mm. The model name is not the size.
1.25 × the highest load, rounded up to the next standard step.
5 A, 1 A or mA. They are not interchangeable.
Five installations, five different answers — and in every one of them the failure was decided before the ratio was ever calculated.
A photo of the cabinet and the load current is enough. We will come back with the model, ratio and class.
Post time: Oct-20-2026
