Overview
The Instrument Transformers 21-151 is an instrument-grade current transformer designed for accurate AC current transformation and measurement in industrial and commercial electrical systems. This 150:5A window-type CT provides reliable current sensing for ammeters, relaying, and metering circuits with high accuracy and burden capability. Rated for 10 kV BIL and available in industry-standard 1.25″ window diameter, the 21-151 delivers consistent performance in panel boards, control panels, and generator applications.
Key Features
- Window-type design for easy installation around single-phase conductors
- 150:5A current ratio for precise measurement of industrial AC loads
- UL recognized (file E93779) and CSA approved (file LR89403)
- Relay class C20, metering class 0.3 B0.1 for both protection and measurement
- Brass stud terminals (No. 8–32) with mounting hardware compatibility
- 10 kV BIL insulation rated for 600V systems
Technical Specifications
- Current Ratio: 150:5A
- Configuration: Single-phase, window-type
- Frequency Rating: 50–400 Hz
- Insulation Level: 600V / 10 kV BIL (full-wave)
- Relay Class: C20
- Metering Class: 0.3 B0.1
- Rating Factor: 2.0
- Window Diameter: 1.25″
- Terminal Type: Brass studs No. 8–32
- Weight: Approximately 10 lbs
- Certifications: UL E93779, CSA LR89403, IEEE C57.13 compliant
Typical Applications
The 21-151 is widely deployed in:
- Panel board ammeter circuits for load monitoring
- Control panel instrumentation and protection relaying
- Engine generator metering and control systems
- Utility and industrial feeder metering
- Power distribution and monitoring circuits
Compatibility & Replacements
Compatible With
- Standard panel-mount ammeters rated 0–5A secondary
- Relay and metering circuits requiring 150A primary sensing
- Industrial AC power systems operating 50–400 Hz
- Control systems requiring IEEE C57.13 compliant CTs
Replaces / Drop-In Replacement For
The 21-151 is interchangeable with other 150:5A window-type current transformers in the same metering and relay class (C20, 0.3 B0.1), including vintage GE ITI and Crompton models with matching specifications. Verify window diameter and terminal configuration before substitution.
Works With
- Analog panel ammeters and meters
- Electromagnetic and solid-state relays
- Power monitoring and energy management systems
- Legacy and modern industrial control systems
- SCADA and utility automation platforms supporting standard CT inputs
