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How CT Sensors Work

How Current Transformer (CT) sensors work, the sensor types Emporia offers, and when to use each.

Current Transformers (CTs) are the sensors that clip around the wires in your electrical panel and tell the Vue how much current is flowing. They're a core part of how the Vue monitors your home. This article covers how CTs work, the sensor types Emporia offers, and when to use each.

How Current Transformers Work

A CT is a split-core clamp built from ferrite, a magnetic material. When current flows through a wire, it creates a magnetic field around the wire. The ferrite core of the CT picks up that magnetic field and produces a small proportional current in the sensor, which the Vue reads.

Because the CT is split, you can open it up, slip it around an existing wire, and close it again. No need to disconnect or cut anything. The CT doesn't touch the conductor itself, so it's a passive measurement with no electrical connection to the monitored line.

All Emporia rigid CT sensors (200A and 50A) output 0.333V at rated current. This is a standard CT output compatible with the Vue 3 gateway.

How the Vue Reads Your Ports

The Vue has two types of ports, and the app treats them differently:

  • Main ports (A, B, C) — always combine into one total. They are dedicated to a single electrical service and cannot be split between two separate loads or services. If you need to independently measure two separate services or feeders, each service requires its own dedicated Vue monitor. See Using Multiple Vues: Parallel Panels and Sub-Panels for setup guidance.

  • Branch ports (1–16) — report individually and are treated as loads downstream of the main service. Branch circuit readings can be merged in the app to combine multiple CTs into one reading.

For full details on port assignments, dedicated monitor configurations, and how port hierarchy affects your energy calculations, see CT Sensor Installation.

Sensor Types

Emporia offers two CT sensor types: 200A Main CTs and 50A Branch CTs. Each is available in multiple variants to accommodate different panel configurations.

For full dimensional specifications and sizing, see the Vue 3 Spec Sheet.

200A Main CT Sensors

200A Main CTs are the primary sensors for measuring whole-home energy consumption. They clamp around your main service conductors and connect to the Vue's three main ports (A, B, or C).

Standard 200A clamp

  • Included in all Vue 3 kits — 2 sensors for single split-phase, 3 for three-phase

  • Large rigid clamp, 5mm screw terminal plug

  • Inner diameter window: 22mm

  • Dimensions: 40mm x 51mm x 70mm

  • Cable length: 40"

  • UL certified rated for 200A

  • Works correctly on any panel size up to 200A including sub-panels — no lower-rated sensor needed

  • Purchase additional 200A Standard CTs

Spring clamp

  • A clip-style alternative to the standard rigid clamp for main conductors. Clips around the wire without tools, no power supply required

  • 5mm screw terminal plug, designed for main ports (A, B, or C)

  • Inner diameter window: 24mm

  • Sold in sets of 2. Three-phase installations require two purchases (4 total)

  • Purchase Spring Clamps

Flexible Sensors

  • Two variants; Red Coils (THIC) and Black Coils (Deyo Tech). See Flexible Sensors below for additional information

  • Wire loops designed for panels where a rigid clamp-on won't fit, such as bus bars, tight spaces, or unusual configurations

  • Require an integrator unit and dedicated power supply — both included with purchase

  • Sold separately on the Emporia shop in 2-coil and 3-coil kits

50A Branch CT Sensors

50A Branch CTs monitor individual circuits and connect to the Vue's numbered side ports (1–16). Up to 16 sensors per Vue. Available variants:

Standard 50A clamp

Large-diameter clamp

  • For branch circuits with larger wiring that the standard 50A clamp won't fit around

  • 3.8mm screw terminal plug, fits branch ports (1–16) — no wiring changes or multiplier needed

  • Inner diameter window: 22mm

  • Outer dimensions: 59.5mm x 44.9mm x 69.7mm

  • Cable length: 5ft (1.5m)

  • Purchase Large-Diameter 50A CT

A note on amperage and safety.

Exceeding a sensor's rated amperage won't damage the Vue or the sensor, the measurement simply caps at the CT sensor and device port's maximum. See CT Accuracy for a full breakdown.

Flexible Sensors (Rogowski coils)

Flexible Sensors replace the standard 200A rigid clamps and plug into the Vue's main ports (A, B, or C). Unlike rigid CTs, they require an integrator unit and dedicated power supply — both included with purchase.

Red Coils (THIC)

Black Coils (Deyo Tech)

Product Documentation

Feedback and Suggestions

This knowledge base is continuously updated to provide the most helpful guidance for Emporia customers. If you found this article unclear or have suggestions for improvement, please contact our Customer Support team.

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