Current Transformers for Electric Submetering

We stock split-core CTs from 100 A to 4000 A with 0.333 V output for the meters we sell, plus wireless CT clamps for points where running secondary leads is impractical.

How to select a CT

• Size to expected load, not to breaker rating. A 600 A CT on a circuit that never exceeds 60 A spends its life in the bottom decade of its range, where accuracy class is not guaranteed. See the 100 A CT and 600 A CT.
• Match the output to the meter. 0.333 V (millivolt) CTs are safe to open-circuit and standard for submetering; 5 A CTs must never be opened under load.
• Split-core for retrofits. Split-core CTs clamp over an existing conductor without disconnecting it, which is what makes no-shutdown retrofits possible.
• Check window size and conductor fit before ordering — the largest CTs, such as the 4000 A CT, are specified as much by physical fit as by rating.
• Wireless CT clamps such as the Milesight CT101 LoRaWAN CT clamp suit remote panels with no meter and no cable path.

Accuracy classes and common mistakes

Accuracy class describes error at rated current, not across the whole range, which is why oversizing is the most expensive habit in submetering. The other recurring errors: reversed CT orientation (negative power readings), phase and CT mismatch across a three-phase set, an unseated split core leaving an air gap, and long unshielded secondary runs. Full detail in CT accuracy classes and revenue-grade metering under ANSI C12.20 and meter selection help for electric metering. CTs pair with the meters in electric submetering.