Our current sensor selection guide covers the choice between sensing technologies — Rogowski coil, Hall effect, and conventional CT. Within the Rogowski coil category specifically, there's a second decision that matters just as much: flexible coil versus rigid (semi-rigid) coil construction.
Why Rogowski Coils Can Be Flexible At All
A conventional current transformer needs a rigid, precisely shaped iron core to function. A Rogowski coil has no iron core at all; it's a precisely wound coil on a flexible, non-magnetic former, which is what makes the flexible version possible in the first place.
Flexible Coils
A flexible Rogowski coil is supplied as an open, rope-like loop that wraps around the conductor and clips closed. This solves two installation problems rigid sensors can't:
Irregular or oversized conductors. Large busbars, cable bundles, or non-circular conductors that don't fit inside any standard rigid clamp diameter can still be wrapped by a flexible coil.
Tight or congested panel spaces. A flexible coil can often be threaded through and wrapped in spaces a rigid sensor simply can't physically access.
The trade-off is generally a small accuracy penalty from positioning sensitivity, on the order of a few percent depending on installation care.
Rigid (Semi-Rigid) Coils
A rigid or semi-rigid Rogowski coil is manufactured as a fixed-shape loop, sometimes split into two halves with a precision locking mechanism. Because the coil geometry is fixed and consistent, rigid coils generally achieve better accuracy and repeatability than a flexible coil installed by hand.
The trade-off: a rigid coil only fits conductors within its designed diameter range, and needs adequate clearance to be positioned during installation.
Comparing the Two
| Factor | Flexible Coil | Rigid/Semi-Rigid Coil |
|---|---|---|
| Fits irregular/oversized conductors | Yes | No — fixed aperture |
| Fits tight, congested panel spaces | Generally yes | Only if clearance allows |
| Accuracy/repeatability | Good, with some installation-dependent variation | Better — fixed, consistent geometry |
| Typical use case | Field installation, busbars, retrofit | Precision measurement, permanent installation |
Practical Selection Guidance
For field service and troubleshooting work where conductor size and panel geometry vary from job to job, a flexible coil set is the more versatile choice. For permanent or semi-permanent installation on a known, fixed conductor, a rigid coil sized correctly delivers better long-term accuracy and repeatability. Many current sensor ranges, MEWOI's Rogowski coil lineup included, offer both variants built around the same underlying coil technology.