html{display:none} SEL-3780 Test Point Voltage Sensor | Schweitzer Engineering Laboratories


Test Point Voltage Sensor

The SEL-3780 can be used in place of other voltage measurement devices, like potential transformers and elbow voltage sensors, to detect system voltage loss where exact system voltage measurement reporting is not required. The sensor installs easily on capacitive test points of distribution elbows, and its embedded logic, self-calibration feature, and wide dynamic sensing range automatically adapt to test points on elbows and t-bodies.

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Monitor Voltage and Detect Outages—The SEL-3780 sensor’s embedded logic provides voltage detection from test points, monitoring the test point voltage of each phase independently and eliminating the need for relay analog inputs for voltage sensors. The sensor provides status information to the follow-on device (e.g., a relay) in a pad-mounted or underground distribution source transfer switch via an output contact. Voltage tracking helps filter out noise, spikes, and variations in voltage that occur normally on distribution systems.

Automatically Transfer Sources—Apply the SEL-3780 in automatic source transfer applications to trigger the operation of the source transfer switchgear upon a loss of voltage. When the sensor detects a loss of system voltage on the primary source that feeds mission-critical loads, it opens its output contact and signals a follow-on device (e.g., a relay) to initiate a transfer.

Simplify Inventory Needs—The SEL-3780 is universally compatible with IEEE 386-compliant elbows and T-bodies and has two simple model variations for capacitive test points and basic insulating plugs, allowing it to cover all applications. Its wide dynamic sensing range accommodates various elbow voltage ratings and underground medium-voltage distribution systems from 2.5 to 35 kVL-L.

Quickly Retrofit Systems—Safely and easily connect SEL-3780 sensors to distribution system test points without cutting existing cables or directly connecting equipment to medium-voltage conductors.


    1. 1
      LEDs to indicate calibration state, phase voltage loss and presence, and output contact state
    2. 2
      Mode selector to initiate self-calibration and select operating modes
    3. 3
      Voltage loss threshold selector to set at 50%, 60%, 75%, or 85% of system voltage
    4. 4

      I/O cable to power SEL-3780 and communicate status of output and alarm contacts 




The SEL-3780 features a simple and powerful self-calibration feature, which eliminates the need to factory-calibrate it to specific elbows. Within seconds of initiating self-calibration via the mode selector, the sensor adapts to the unique voltage output of each test point and stores the calibration set points within its nonvolatile memory.

Automatic Voltage Tracking

The SEL-3780 tracks the test point voltage of each phase independently, and it uses a long-term rolling average function to adapt to voltage variation over time. The sensor starts tracking system voltage after the user initiates self-calibration.

Simple Installation

Use industry-standard hot-line tools to attach the sensor to capacitive test points or to basic insulating plugs without having to disconnect a distribution elbow. The sensor’s control box can be magnetically attached to the pad-mounted enclosure or fastened to a vault wall.

System Integration

The SEL-3780 can be universally applied to IEEE 386-compliant elbows and T-bodies with test points across all distribution voltage classes (2.5–35 kVL-L).

Secure Operation

The SEL-3780 continuously monitors itself to notify the user and relay of any incorrect operation. The alarm contact provides follow-on device (e.g., a relay) with the status used to block the output contact status in the event of a system or device error.

Test point type
  • Capacitive test point
  • Basic insulating plug
Sensor cable length: 12 ft or 20 ft
I/O cable length: 25 ft or 50 ft
  • Adapter Ring Kit for Capacitive Test Point
  • Magnet Mount Kit for SEL-3780 and SEL-8300
  • Sealing Kit for Basic Insulating Plug
  • SEL-MCG Magnetic Cable Guide

The Firmware IDs for older versions of the firmware can typically be found in Appendix A of the instruction manual.

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