If you’re working with energy meters, protection relays, or industrial panels, chances are you’ll need a current transformer (CT) — but choosing the right one isn’t always obvious.
At Duncan Instruments, we stock a wide range of ANSI-rated, CSA-compliant CTs for professional use across Canada. This quick guide will help you understand what a CT does, how to choose the right ratio, and what form factor best suits your application.
⚡ What Does a Current Transformer Do?
A CT safely reduces high electrical current to a smaller, measurable value — usually from hundreds of amps down to 5 A or 1 A. This allows your meter, analyzer, or relay to read the current accurately without being exposed to dangerous levels.
Without a CT, many systems wouldn’t work at all — and worse, they wouldn’t be safe.
🔢 What Do CT Ratios Like 600:5 Mean?
The ratio indicates how much the CT steps down the current.
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A 600:5 CT will produce a 5 A output when sensing 600 A.
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Choose a ratio that closely matches your system’s expected load for best accuracy.
We stock popular options like 100:5, 200:5, 600:5, and 800:5 — all rated for 600 V systems.
🧱 Which CT Form Factor Do You Need?
We carry several styles to fit different installations:
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Ring-type (solid core): High accuracy, ideal for new builds
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Split-core: Opens for easy retrofit around existing wires
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Square case: For panel mounting, often used with bus bars
Each has its place. Not sure? Just ask us.
🛠️ Where Are CTs Used?
Current transformers are essential in:
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Energy monitoring systems
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Ground fault relays like our GFR-2
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Power analyzers
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Control and distribution panels
If your system measures current or trips on current — a CT is involved.
🔗 Browse Our Current Transformers
Looking for a reliable CT? We stock ANSI 600 V class models in multiple ratios and mounting types — ready to ship across Canada.
Have questions? Call us at <a href="tel:4167424448">416-742-4448</a> or request a quote. Since 1968, we’ve been Canada’s trusted source for precision test equipment and support.