Complete technical specifications for 750:5 current transformers. This guide covers accuracy classes for metering and protection, burden ratings, physical dimensions, and application recommendations for 750-Amp circuits.
⚡ 750:5 CT Quick Reference
750:5
150:1
Class 0.5
5P20
Understanding the 750:5 CT Ratio
A 750:5 current transformer reduces 750 Amps of primary current to 5 Amps of secondary current, providing a 150:1 step-down ratio. This allows high-current circuits to be safely monitored using standard 5-Ampere meters and relays.
📐 Calculation Example
If your ammeter connected to a 750:5 CT reads 3.5 A:
Primary Current = 3.5 A × 150 = 525 Amps
Technical Specifications for 750:5 CTs
| CT Ratio | 750:5 (150:1) | ||
| Primary Current Rating | 750 A | Secondary Current | 5 A |
| Metering Accuracy Class | Class 0.5 | Protection Accuracy Class | 5P20 |
| Burden Rating | 15.0 VA | Knee Point Voltage (est.) | ~450 V |
| Window Size (typical) | 3.0″ diameter | CT Type | Solid Core |
| Frequency | 50/60 Hz | Insulation Class | 0.6 kV (LV) |
Accuracy Class Explained
Standard metering accuracy (IEC Class 0.5). ±0.5% ratio error at rated current. Common for energy management.
Protection class (IEC 5P20). Maintains 5% composite error up to 20× rated current for reliable fault detection.
Burden Rating: 15.0 VA
Standard burden (15.0 VA). Compatible with most analog and digital meters, plus short cable runs.
Application Guide for 750:5 CTs
Typical Use Cases
- Industrial main switchgear
- Medium voltage (MV) feeders
- Substation bus metering
- Generator output monitoring
CT Selection Considerations
When to Choose 750:5 Ratio
- Load Current: Use when expected maximum load is 450 – 750 Amps. The CT should be sized so normal operating current is 60-80% of CT rating for optimal accuracy.
- Conductor Size: This CT has a 3.0″ window, suitable for conductors up to approximately 1500 MCM or 7″ bus bar.
- Turns Ratio: 150:1 reduction. Secondary current = Primary / 150.
When to Choose Adjacent Ratios Instead
| Condition | Recommended Ratio | Reason |
|---|---|---|
| Load is typically below 375A | 550:5 | Operating at higher % of CT rating improves accuracy at lower currents |
| Load may exceed 750A occasionally | 950:5 | Prevents CT saturation during peak loads or motor inrush |
| Conductor won’t fit 3.0″ window | Larger window CT or Split-Core | Consider split-core for retrofit without de-energizing |
Frequently Asked Questions about 750:5 CTs
❓ What does a 750:5 CT ratio mean?
❓ How do I calculate the primary current from the secondary reading on a 750:5 CT?
Formula:
Primary Amps = Secondary Amps × 150Example: If the meter reads 2.5A, the primary current is 2.5 × 150 = 375 Amps.
❓ Can I use a 750:5 CT with a 1A secondary meter?
❓ What happens if the primary current exceeds 750A?
Compliance & Standards
Current transformers should comply with the following industry standards for accuracy and safety. For official standard documents, visit IEC or IEEE.
- IEC 61869-2: Instrument transformers – Part 2: Additional requirements for current transformers
- IEEE C57.13: IEEE Standard Requirements for Instrument Transformers
- ANSI C12.1: American National Standard for Electric Meters – Code for Electricity Metering
- IEC 60044-1: Instrument transformers – Part 1: Current transformers (superseded by IEC 61869)
- NIST Handbook 44: Specifications for Current Transformers Used in Metering
For more background on current transformer principles, see the Wikipedia article on Current Transformers.
Explore Related CT Ratios
| ← 600:5 CT | 750:5 (Current) | 800:5 CT → |
Related Resources
📚 Current Transformer Guide
Complete CT fundamentals
📊 CT Ratio Selection Chart
Compare all CT ratios
📝 About This Guide
This technical specification guide is compiled by the Transformer4U Engineering Team, drawing from industry standards (IEC 61869-2, IEEE C57.13) and manufacturer datasheets.
Disclaimer: Specifications shown are typical values. Actual specifications vary by manufacturer and model. Always verify with the specific CT datasheet. Last updated: January 2026