CT Metering Basics: When Whole-Current Won't Do
Above 100A per phase, metering moves to current transformers. What CT metering involves and what it means for the switchboard.
The 100A threshold
Whole-current meters carry the full load through the meter itself and top out around 100A per phase. Beyond that, current transformers scale the current down to a metering-class signal — the meter reads the ratio, not the raw load.
What the board must provide
A CT metering installation needs a CT chamber sized to network requirements, test links, correctly rated and classed CTs, and secure sealable covers. These are fabrication items — designed into the switchboard, not added afterwards. Confirm the applicable network specification for the site.
Coordinate early
CT chamber dimensions, viewing windows and sealing provisions vary between networks. Confirming the requirement before fabrication keeps the board approval clean and avoids the most expensive class of rework.
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