Size marking on the case is the bare core dimension (OD × ID × H), not the cased or finished size.
Nanocrystalline toroidal core 30×20×10 mm
30×20×10 mm nanocrystalline toroidal core, Blue PBT Class B 130C.
CCNT-030-020-010-MFBL is a 30×20×10 mm nanocrystalline toroidal core for ground-fault CTs, metering CTs, and medium-frequency transformers. Its 20 mm inner diameter supports practical secondary windings, while high-permeability nanocrystalline material helps achieve useful magnetizing inductance at low turns. Choose this size when winding window, magnetic area, and envelope must stay in balance for the target current or VA.
Technical Specifications
Bare core dimensions
Cased / finished dimensions
Magnetic properties
Finish and handling
Environmental
Applications and selection
Applications
- ground-fault CTs
- metering CTs
- medium-frequency transformers
- protective relaying
- ground-fault protection current transformers
- revenue-grade metering CTs
- medium-frequency (400Hz–20kHz) power transformers
- protective relaying current sensors
When to choose this size
This 30×20×10 mm toroidal core is sized for ground-fault CTs and related designs in the nearby size family. Step down to the 25×16×10 mm core when board space, enclosure height, or a tighter footprint matters more than winding room. Within the same 30 mm OD, the 30×20×12 mm core adds stack height and Ae when you need more VA or easier secondary winding without growing the outer diameter. Move up to the 40×25×15 mm core when you need a larger outer diameter, winding window, or higher throughput than this part can comfortably support. In short, pick CCNT-030-020-010-MFBL when your design for ground-fault CTs fits this window and OD; pick a neighbor when compactness or power handling shifts the trade-off.
Winding notes
Magnetic calculations should use the bare 30×20×10 mm geometry (Ae 0.41 cm², Le 7.85 cm). The winding must fit the finished window: cased ID is 17.6 mm, not the 20 mm bare ID. Keep the winding distributed around the toroid to limit leakage and local heating. High permeability (μi 80,000) supports useful magnetizing inductance at practical turn counts; stay within 1.25 Tesla saturation and the -40°C to +130°C PBT Class B 130C limit.
Related application guides
Frequently asked questions
Are stated dimensions bare or cased?
The 30×20×10 mm size marked on the case is the bare core (OD × ID × H). Finished cased size is 33 × 17.6 × 13.2 mm. Use bare dimensions with Ae and Le for magnetic design, and the finished inner diameter for winding clearance.
Is this core suitable for a current transformer?
Yes. It is a nanocrystalline core sized for ground-fault CTs, including ground-fault protection current transformers. High permeability helps you reach useful secondary inductance with practical turns in a 30 mm OD.
When should I choose a different size instead?
Within the same OD, choose the 30×20×12 mm core for more stack height and Ae. Move up to the 40×25×15 mm core for a larger outer diameter, or step down to the 25×16×10 mm core when board space matters more than this 30×20×10 mm envelope.
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