Current Transformers Without the Headache: A Buyer's Identification Chart

A current transformer (CT) is a small part with a big job: it scales hundreds or thousands of amps down to a safe 5 A (or 1 A) signal your meter can read. Order the wrong ratio or class and your whole metering installation reads fiction. The chart above shows the six CT families we ship most — here's the friendly version.

The 6 CTs on the Chart

Split core CT (2000/5 A, Class 0.5, 720 V)

The retrofit hero. It opens like a clamp and snaps around an existing cable or busbar — no disconnection, no downtime. If the panel is already live, you want split core.

Metering CT (1600/5 A, Class 1.0)

Solid-core workhorse for new panels, 3 kV AC dielectric test, 720 V working voltage. The default choice when you're building the panel anyway.

Wound CT (250/5 A, 50 turns)

Primary wound into the transformer itself — used for lower currents where a bar or cable primary isn't practical.

Toroidal CT (150/5, MES 62/30)

The classic doughnut. Cable passes through the window; compact, cheap, reliable. The volume seller for panel builders.

Busbar CT (800/5, MES 104/80)

Bigger window, built to slide over copper busbar. High accuracy, outdoor-rated options — the one for switchgear and distribution boards.

Toroidal plastic CT (RCT series)

High-precision toroid in a sealed plastic case, 50/60 Hz — for metering OEMs who embed CTs inside their own equipment.

How to Order a CT Without Mistakes

1. Ratio first — match the primary to the load current (e.g. 2000/5 A), secondary usually 5 A.
2. Class — 0.5 for billing-grade metering, 1.0 for general monitoring.
3. Window size — the cable or busbar must physically fit; check the inner diameter against your conductor.
4. Type — split core for retrofits, solid/toroidal/busbar for new builds.
5. Voltage — confirm working voltage (e.g. 720 V AC) and dielectric test for your system.

Why Panel Builders Reorder From Yomin

Consistent ratios, real Class 0.5 performance, tested windings and fast OEM labelling. Pair them with our DIN rail meters for a complete metering set — many buyers order CTs and meters together in one carton. Browse the current transformer range, read the supplier guide, or request a quotation with your ratio list.

FAQ

Can I use a split core CT for billing?

Yes if it's Class 0.5 (or better) and installed per the utility's metering rules — our split cores are built for metering duty.

What happens if I leave a CT secondary open?

Never do it — an open-circuited CT can develop dangerous voltage. Always short or connect the secondary before energising.

Do you make custom ratios?

Yes — custom ratios and window sizes are standard OEM work. Send your list and quantities.

Conclusion

Ratio, class, window, type, voltage — five numbers and you've ordered the right CT. Send us your ratio list and get factory-direct pricing.