What Is a Rogowski Coil Current Sensor?

A Rogowski coil is an electrical device that measures alternating current (AC) by sensing the magnetic field around a conductor. Unlike an iron-core CT, a Rogowski coil is typically air-cored and flexible. The coil produces a small voltage related to the changing current, which is why many applications use an integrator (or a meter with an internal integrator) to convert that signal into a current-proportional measurement.

Practical takeaway: Rogowski coils are a strong choice for measuring large AC currents safely and non-intrusively, especially when installation space is limited or conductor geometry makes rigid sensors difficult.

Why Use a Flexible Rogowski Coil vs a Rigid Split-Core CT?

Flexible Rogowski coils are often selected when conventional CTs are unsuitable. Common reasons include:

• Easier placement around large bus bars, cable bundles, and crowded breaker panels.
• Wide usable range for many real-world monitoring applications, including high current loads.
• Simple retrofit installs when shutdown time needs to be minimal.
• Improved fit when conductor sizes vary or the panel layout is tight.

If you are building an energy monitoring system, submetering a facility, or commissioning power equipment, flexible coils can help you measure current without disturbing the conductor. Getting accuracy comes down to correct placement and wiring.

RoCoil CTRCFX Key Specs (Quick Reference)

The DENT RoCoil CTRCFX series is designed for accurate, non-intrusive AC current measurement, with multiple coil lengths and lead options. Some systems may require an integrator or compatible meter input depending on your measurement device.

Electrical Performance

• Current range: 5–4000A
• Output: 131 mV/1000A @ 60 Hz. 109.2 mV/1000A @ 50 Hz
• Phase shift: < 0.2° at 50/60 Hz
• Linearity: ± 0.2%
• Frequency: 50/60 Hz
• Temperature sensitivity: 0.07% per °C
• Accuracy note: Best accuracy is achieved when the RoCoil is centered on the conductor.

Mechanical Options

• Lengths: 17”, 24”, 36”, and 47” options
• Typical lead lengths: 3 m, 7 m, and 15 m variants (some may be special order)
• Coil material: flame retardant UL 94 V-0 rated thermoplastic rubber
• Shielding: shielded transducer and output lead for improved noise performance

Safety Ratings

• Working voltage: 600V CAT IV. 1000V CAT III
• Dielectric strength: 7400 VAC around coil. 1000 VAC rated leads
• Certifications listed: ANSI/CAN/UL 2808, CSA C22.2 No. 61010-1-12, IEC 61010 series, IEC 60529

Manufacturer reference: DENT Instruments UL 2808 RoCoil Series (Rogowski Coil Flexible Current Sensors)

Step-by-Step Installation Checklist

All work should be performed by a qualified electrician using proper safety procedures and PPE.

1. Open the coil. Squeeze the connector and pull apart.
2. Wrap around the conductor. Place the RoCoil around the load conductor you want to measure.
3. Confirm direction. Follow the arrow on the coil. It should point toward the load.
4. Close and lock the connector. Ensure the conductor is inside the coil window and the connector is fully seated.
5. Wire to the meter correctly.
   • Connect the CT negative lead to the negative terminal on the measuring device.
   • Connect the CT positive lead to the positive terminal on the measuring device.
   • Connect the bare wire to shield/ground. This helps reduce interference and improves accuracy.
6. Repeat for additional circuits. Install additional coils one at a time, then terminate to the correct channels.

Note on lead colors: Lead colors can vary by model or revision. Always verify the markings on your specific coil and your meter’s polarity requirements before energizing.

Accuracy Tips. Placement Matters

Rogowski coils are commonly specified and calibrated with the conductor centered in the coil window. In real panels, the coil can hang on the conductor, which can introduce error. If you see readings that do not match expectations, start with placement and connector position before assuming the meter is wrong.

Best Practices for More Accurate Readings

• Center the conductor in the coil window as much as possible.
• Keep the connector off the conductor. Rotate or support the coil so the connector is not resting on the measured cable.
• Use the shield wire and land it correctly. Shield termination helps reduce interference.
• Mind nearby conductors. Keep other energized conductors reasonably separated from the coil when possible.
• Stay inside the rating. Confirm the conductor’s maximum current does not exceed the CT’s rating.

If you are commissioning an electrical submetering setup, these placement and wiring details are usually the difference between good readings and frustrating troubleshooting.

Compliance and Documentation. UL 2808, CE, and RoHS

For specification-driven projects, audits, and submittals, documentation matters. RoCoil CTRCFX documentation supports CE and RoHS compliance and references relevant safety standards. If your customer or engineer requests paperwork, include the datasheet, installation instructions, and declaration of conformity in your job folder.

• EU Low Voltage Directive (LVD): Directive 2014/35/EU
• RoHS 3: Directive 2015/863/EU (with EN IEC 63000:2018 documentation reference)
• Safety standards referenced: ANSI/CAN/UL 2808 Ed.3, CSA C22.2 No. 61010-1-12 Ed.3

Shop ZotSupply Power Monitoring Categories

Need current sensing and metering components for your monitoring project? Use these ZotSupply category pages to narrow down the right fit.

• Power Monitoring
• Metering Current Transformers
• Electrical Submetering (Brand Filter)

If you are not sure which sensor length or lead length is best, send ZotSupply your conductor size, expected current range, and meter model. We can help you match the coil and the meter input requirements so your commissioning goes smoothly.

FAQ

Do Rogowski coils work on DC current?

Rogowski coils are intended for AC measurement and for current pulses where the changing magnetic field can be sensed. Many systems use an integrator to obtain a signal proportional to current.

What causes inaccurate readings with flexible Rogowski coils?

Placement is a major factor. Error increases when the coil hangs and the connector rests on the conductor. Center the conductor, keep the connector off the conductor, and land the shield properly.

What is the output of the RoCoil CTRCFX series?

The CTRCFX output is commonly specified as 131 mV per 1000A at 60 Hz and 109.2 mV per 1000A at 50 Hz for 50/60 Hz applications.

How do I wire the RoCoil leads?

Connect CT negative to the meter negative terminal, connect CT positive to the meter positive terminal, and connect the bare wire as shield/ground to reduce interference. Verify lead markings and polarity for your exact model and meter.