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Split-core vs solid-core current transformers

Electrically they do the same job. The decision is almost entirely about whether you can afford to disconnect the conductor — and what that downtime is worth.

The short answer

Retrofitting a live installation? Split-core. It clamps around the existing cable, so metering gets added in a maintenance window instead of an outage. The unit costs more and the installed cost is usually lower.

Building a new panel? Solid-core. The conductor is being terminated anyway, the unit price is lower, and a closed ring cannot be opened later by someone else working in the board.

The accuracy argument is mostly theoretical. A properly fitted split-core CT performs to its class — the failure mode is installation, not design.

Side by side

The trade-offs that actually decide the specification.

ConsiderationSplit-core (clamp-on)Solid-core (ring)
InstallationClamps around existing cableCable must pass through the ring
Requires shutdownNoYes — conductor must be disconnected
Retrofit to a live boardYesNot practically
Typical fitting timeMinutesDepends on the isolation window
Accuracy potentialVery goodMarginally better at the top end
Sensitivity to fittingYes — core faces must close cleanlyLow — closed magnetic path
Cost per unitHigherLower
Total installed costUsually lowerHigher once downtime is counted
Risk of being moved laterHigher — it can be openedLower
Best forRetrofit, audits, temporary studiesNew build, permanent switchgear

Where split-core installations go wrong

Nearly every accuracy complaint about split-core CTs traces back to fitting rather than to the device. The core has two mating faces that must close cleanly and completely — if they are contaminated, burred, or held slightly apart by a cable tie or a stiff cable, the magnetic path is compromised and the reading suffers.

Three things worth checking at commissioning: that the faces are clean and fully latched, that the CT is oriented correctly for direction of current flow, and that the primary is centred rather than pressed against one side of the aperture. All three are quick to verify and all three are commonly missed.

Verifying against a known reading at commissioning catches all of them in a couple of minutes, and is worth doing before anyone starts billing off the data.

Where Tech OVN uses each

Titan Audit is designed around split-core CTs covering 10 A to 1000 A primary, because audits and temporary studies cannot generally justify a shutdown. The same property makes it the sensible choice for adding metering to facilities that cannot take an outage at all.

Titan is normally specified with permanent CTs for fixed installation, where the panel is being built or modified anyway. Split-core is available on request where a retrofit needs it.

Frequently asked questions

A solid-core current transformer is a closed ring — the conductor has to be disconnected and threaded through it. A split-core CT opens on a hinge so it can be clamped around a cable that is already in place. Electrically they do the same job; the difference is entirely about how they are installed and what that costs you in downtime.
That is the reason they exist. Because the core opens, the CT can be fitted around an existing conductor without breaking it, which means metering can be added to a live installation during a normal maintenance window rather than a planned outage. Local electrical safety rules and permit-to-work procedures still apply, and the work should be done by a competent person.
In principle a closed magnetic path is slightly better, and at the very top of the accuracy range solid-core has an edge. In practice a well-made split-core CT that is correctly fitted performs to the same class as its solid-core equivalent. The real accuracy risk with split-core is not the design but the installation — if the mating faces are dirty, damaged or not fully closed, the error introduced dwarfs any inherent difference.
Split-core, without much hesitation. An audit is time-boxed and usually cannot justify shutting down the circuits being studied. Split-core CTs let you instrument a board in minutes, run the study, and then either remove the equipment or leave it in place for continuous monitoring. Titan Audit is built around exactly this workflow, with split-core CTs covering 10 A to 1000 A primary.
Solid-core, generally. In new build the conductor is being terminated anyway, so threading it through a ring costs nothing extra, the unit price is lower, and a closed core cannot later be opened by someone working in the panel. The argument for split-core disappears when there is no downtime to avoid.
Size the CT to the circuit's actual load rather than its breaker rating. A CT sized for a 400 A breaker on a feeder that draws 60 A will spend its life at the bottom of its range, where accuracy is worst. If the load is very low relative to the rating, a smaller CT — or a meter specified to hold accuracy at low load — is the better answer.
Split-core CTs are the standard approach in facilities that cannot take an outage. In most cases the constraint turns out to be change control and permit-to-work rather than the engineering, so it is worth involving the facilities team early.

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Adding metering to a live installation?

Send us the board schedule and load ratings — we'll tell you which CTs to use and whether it can be done without an outage.

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