Finding the right current transformer (CT) shouldn’t slow down your project. Whether you're ordering for a panel build, submetering retrofit, or routine maintenance, this guide walks you through how to choose the correct CT — quickly, confidently, and without guesswork.
🔍 What Is a Current Transformer?
A current transformer (CT) steps down high AC current to a safe, measurable level — typically 5A — for use in metering or control circuits. For example, a 600:5 CT outputs 5 amps on its secondary when 600 amps flow through its primary.
At Duncan Instruments, we stock hundreds of CSA-approved CTs with standard ratios like 50:5, 100:5, 600:5, and 1000:5 — all ready to ship from Canada.
🧩 Three Key Specs You Need to Know
1. Current Ratio
Printed on every CT (e.g., 600:5). Match this to your system’s maximum expected current. If in doubt, check the breaker or main feed ratings.
2. Window Size
This defines the opening your conductor passes through.
We make it easy: our model numbers are based on the window size. For example, 2SFT = 0.75" opening.
3. CT Style: Mounting & Shape
All our CTs are solid core and available in the same range of window sizes. The key difference lies in their body design and mounting configuration:
-
SFT – Round core with compact form factor and basic mounting
-
SHT – Same core sizes as SFT, but with an extended body and flanged mounting feet
-
RL – Rectangular housing with low profile, ideal for panel retrofits
-
DRL – Same rectangular shape as RL, with extended tabs for more stable mounting
Each model is offered in both:
-
Control accuracy (e.g., SFT, SHT, RL, DRL)
-
Metering accuracy (e.g., ASFT, ASHT, ARL, DARL)
🛠️ Built to Meet Canadian Standards
All models are:
-
CSA certified
-
Rated for Class 1 accuracy
-
Suitable for commercial and industrial use
Common applications include:
-
Panel metering
-
Motor load monitoring
-
Sub-distribution panels
-
Energy management systems
✅ We Make CT Selection Easy
We’ve structured our store to make choosing a CT frictionless:
-
Clear naming = clear sizing
-
Product pages with dropdowns for ratio and window size
-
Technical specs and dimensional drawings included
-
All CTs stocked in Canada and priced dynamically for value
Need help selecting the right model? Contact our team — we're fast and helpful.
🔗 Explore Our CT Series:
Or see the full Current Transformers Collection for all options.