Current Transformers
A current transformer (CT) steps down a high primary current to a small, standard secondary signal, typically 5A or 1A, that a meter or protection relay can safely read. NLS Power sources CTs to IEC 61869-2, in metering and protection accuracy classes, sized to the busbar or cable current a project's switchboard and metering schedule specifies.
A current transformer takes the current flowing through a busbar or cable, often several hundred or several thousand amps, and produces a proportional secondary current, standardized to 5A or 1A, that's small and safe enough to feed a meter, a protection relay, or both. Without a CT, no meter or relay at the switchgear or MDB level could be built to handle the primary current directly; the CT is what makes metering and protection at high current practical at all.
CTs split into two accuracy families that serve different jobs. Metering CTs, with accuracy classes like 0.2S, 0.5 or 1 under IEC 61869-2, are built to stay accurate across the normal load range and to saturate deliberately at high fault current, protecting the meter downstream from a current spike it was never meant to see. Protection CTs, classed 5P or 10P, are built the opposite way: they're allowed looser accuracy in normal operation but have to stay linear at high fault current, because a protection relay needs an accurate reading precisely during the fault the metering CT is designed to ignore.
Burden, the load the CT's secondary can drive without losing accuracy, expressed in VA, has to match what's actually connected: a long cable run from the CT to a remote meter or relay adds resistance that eats into the available burden, and undersizing this on a long run is a common design error, one that shows up as inaccurate readings only after the equipment is installed and running.
CTs are supplied as wound-primary types for lower current ratings and bar-primary (window) types, where the busbar itself passes through the CT window, for the higher current ratings typical inside LV switchgear and MDBs.
NLS Power sources CTs to IEC 61869-2 in both metering and protection accuracy classes, ratio and burden matched to the switchboard's current rating and the meter or relay it feeds. Quoting works from the primary current, the required accuracy class, and the burden needed at the far end of the wiring run; NLS Power returns pricing in USD, typically bundled with the panel meter or switchgear order it serves.
Specifications
- ✓To IEC 61869-2, current transformer standard
- ✓Metering accuracy classes: 0.2S, 0.5, 1, designed to saturate at high fault current to protect connected meters
- ✓Protection accuracy classes: 5P, 10P, designed to stay linear through fault current
- ✓Secondary current standardized to 5A or 1A depending on switchboard design
- ✓Wound-primary and bar-primary (window) construction depending on primary current rating
- ✓Burden (VA) sized to the actual connected load and wiring run length
Frequently Asked Questions
What's the difference between a metering CT and a protection CT?+
A metering CT stays accurate at normal load and deliberately saturates during a fault to protect the meter. A protection CT is allowed looser normal-load accuracy but must stay linear through fault current, since a relay needs an accurate reading precisely then.
Who supplies current transformers matched to a switchboard schedule in Saudi Arabia?+
NLS Power sources CTs to IEC 61869-2 in metering and protection accuracy classes, with ratio and burden matched to the switchboard current rating and the meter or relay it serves.
Why does the wiring distance to a CT matter?+
A long lead from the CT to its meter or relay adds resistance that consumes part of the CT's rated burden. If the burden isn't sized for that distance, the reading at the far end can be inaccurate even though the CT itself is correctly rated.