Your Trusted Current Transformer Calibration Provider
Micro Precision is an ISO/IEC 17025:2017 accredited calibration provider with NIST-traceable reference standards and more than 50 laboratories operating across North America, Latin America, Europe, Asia, and the Middle East. As part of our broader electrical calibration services portfolio, we calibrate fixed, installed current transformers used in utility metering, switchgear, and protection circuits found in power generation, transmission, and industrial facilities.
Because current transformers carry safety, protection, and revenue metering responsibilities, calibration accuracy directly affects protection coordination, billing integrity, and audit readiness. Micro Precision’s accredited process verifies ratio accuracy, polarity, burden, and insulation resistance against traceable reference standards, producing documented results accepted by utilities, industrial facilities, and third-party auditors.
Micro Precision provides ISO/IEC 17025:2017 accredited, NIST-traceable calibration for fixed, installed current transformers used in utility metering, switchgear, and protection circuits. Our global network of more than 50 laboratories delivers documented ratio, polarity, burden, and insulation resistance test results for power, energy, and industrial facilities worldwide.
Not a handheld current probe: Current transformers are permanently installed, hard-wired instrument transformers mounted in switchgear, substations, and metering panels. They are distinct from handheld, clamp-style current probes used with meters and oscilloscopes. For handheld current probes used with meters and oscilloscopes, see our current probe calibration services page.
Why Current Transformer Calibration Matters
Current transformer calibration matters because ratio and phase errors in a miscalibrated CT distort protection relay operation and metering accuracy, creating safety hazards and billing discrepancies that are difficult to detect without formal testing. An out-of-tolerance CT can cause a protection relay to under-trip or over-trip, or cause a revenue meter to register incorrect energy consumption.
ANSI/NCSL Z540.3 requires documented calibration with objective evidence for measuring and test equipment used in regulated processes, and ISO 10012 establishes measurement management system requirements including calibration intervals and traceability. For quality managers, a documented CT calibration certificate is the evidence auditors expect. For procurement officers, working with an accredited power and energy industry calibration provider reduces vendor risk and simplifies compliance sourcing.
Lab technicians and compliance officers rely on standardized CT test data, ratio, polarity, burden, and insulation resistance results, to confirm protection systems function correctly between maintenance cycles. Micro Precision documents each result under its ISO/IEC 17025:2017 accreditation, giving every stakeholder a consistent, audit-ready record.
Ensure Accurate Current Transformer Calibration
Accurate current transformer calibration requires a structured process that verifies ratio, polarity, burden, and insulation resistance against traceable reference standards before the CT returns to service. Micro Precision follows a documented workflow for every current transformer received, performed under the controls required by our ISO/IEC 17025:2017 accreditation.
The process for each current transformer includes:
- Receipt and inspection — nameplate data, ratio, accuracy class, and physical condition are verified on arrival or at the installation site
- Ratio and phase test — primary and secondary values are compared against the nameplate ratio to confirm accuracy class using calibrated test equipment
- Polarity check — winding orientation is confirmed to ensure the correct phase relationship for protection and metering circuits
- Burden verification — performance is checked at the specified burden to confirm accuracy is maintained under rated operating conditions
- Documentation and certification — a certificate of calibration is issued documenting as-found and as-left data, test results, and the NIST traceability chain
- Return — the CT is returned to service or shipped back with its calibration certificate
Standard and rush turnaround options are available for outage-critical schedules and planned maintenance windows. Contact our team to discuss current lead times.
Our Calibration Options
Micro Precision offers both in-lab and on-site current transformer calibration, part of our full range of instrument calibration services, to match the realities of fixed, installed CT equipment. Because current transformers are typically hard-wired into switchgear, substations, and metering panels, on-site calibration is often the practical choice for utility and industrial facilities.
On-Site Calibration
For current transformers permanently installed in switchgear or substation equipment, Micro Precision sends qualified technicians to your facility with NIST-traceable reference standards. On-site calibration verifies ratio, polarity, burden, and insulation resistance in place, eliminating the cost, downtime, and safety risk of de-installing a hard-wired instrument transformer.
In-Lab Calibration
Ship a current transformer to one of our accredited laboratories for full-capability testing under controlled conditions. In-lab service supports the complete range of documentation options, including ISO/IEC 17025:2017 accredited certificates with measurement uncertainty statements.
Rush Turnaround
Standard and rush calibration turnaround options are available for both in-lab and on-site service. Contact our team to discuss current lead times for outage-critical schedules.
Current Transformers We Calibrate
Micro Precision calibrates a variety of current transformers used in utility metering, switchgear, and protection applications across power, energy, and industrial facilities.
- Utility revenue metering current transformers (multiple accuracy classes)
- Switchgear-mounted protection current transformers
- Substation current transformers
- Bushing-type current transformers
- Wound-type current transformers
- Window and toroidal-type current transformers
- Multi-ratio current transformers
- Low-voltage and medium-voltage current transformers
If your current transformer model, accuracy class, or configuration is not listed, contact our team. Micro Precision supports a wide range of CT types beyond those shown here, including instruments verified with test equipment such as the Omicron CT Analyzer.
Calibration Service Levels Offered
Micro Precision offers service levels to match your quality program requirements, from NIST-traceable certificates to fully accredited calibration documentation with measurement uncertainty statements.
| Type of Service | Traceable | Traceable with Data | Accredited (ISO:IEC 17025:2017, Z540.3) |
|---|---|---|---|
| Calibrated to manufacturers specifications traceable to SI Units | |||
| ISO 9000 Compliant | |||
| Calibration certificates, data, maintained on secure web based tool (CDM) | |||
| Detailed calibration certificates and calibration stickers | |||
| Instrument adjustment (if found out of tolerance) | |||
| ANSI/NCSL Z540-1 compliant | |||
| Calibration Data | |||
| Logo from Accreditation body, Expanded Measurement Uncertainty | |||
| ANSI/NCSL Z540.3 compliant |
Current Transformer Calibration Services
Micro Precision delivers ISO/IEC 17025:2017 accredited, NIST-traceable calibration for fixed, installed current transformers used in utility metering, switchgear, and protection circuits, covering ratio, polarity, burden, and insulation resistance testing. With more than 50 laboratories worldwide and both in-lab and on-site service, Micro Precision supports utilities, power and energy providers, and industrial facilities with documented, audit-ready calibration results. Submit a request to discuss your current transformer inventory, service level requirements, and turnaround options.
Please complete our quick current transformer equipment calibration & repair service request form, and a Micro Precision representative will reach out to you same-day during office hours, or within one business day after office hours. (Mon – Friday 8AM – 4PM PST)
Current Transformer Service
If you have any inquiries, or simply wish to connect with us, we'd love to hear from you! Please don't hesitate to reach out to us.
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Frequently Asked Questions
Micro Precision calibrates a current transformer by testing it against NIST-traceable reference standards to verify ratio accuracy, polarity, burden, and insulation resistance. Technicians apply a known primary current, measure the secondary output, and compare results to nameplate specifications. Findings are documented on a certificate of calibration under our ISO/IEC 17025:2017 accreditation.
Current transformer calibration frequency depends on your quality program, operating environment, and applicable standards such as ANSI/NCSL Z540.3 and ISO 10012, which call for defined, documented calibration intervals. Utilities and industrial facilities typically schedule calibration on a recurring interval tied to their quality management system. Micro Precision documents the calibration date on every certificate issued.
A current transformer is a permanently installed, hard-wired instrument transformer mounted in switchgear, substations, or metering panels to step down high currents for protection and metering circuits. A current probe is a handheld, clamp-style accessory used with a meter or oscilloscope for temporary measurements. Micro Precision calibrates current probes separately through its current probe calibration services.
Current transformer calibration includes a ratio test comparing primary and secondary current values, a polarity test confirming correct winding orientation, a burden test verifying performance under the connected load, and an insulation resistance test checking dielectric integrity. Micro Precision performs all four tests and documents results on the calibration certificate.
Current transformer calibration references quality management standards including ANSI/NCSL Z540.3 and ISO 10012, which govern calibration intervals, measurement traceability, and documentation. Micro Precision performs calibration under its ISO/IEC 17025:2017 accreditation, with results traceable to NIST. These standards give quality managers and auditors objective, verifiable evidence of instrument accuracy.
Yes. Micro Precision provides on-site current transformer calibration for units permanently installed in switchgear, substations, or metering panels where removal is impractical. Qualified technicians travel to your facility with NIST-traceable reference standards to perform ratio, polarity, burden, and insulation resistance testing in place, minimizing downtime and avoiding costly de-installation.
A current transformer calibration certificate documents the instrument identification, calibration date and interval, test results for ratio, polarity, burden, and insulation resistance, as-found and as-left data, and the NIST traceability chain. Micro Precision issues certificates under its ISO/IEC 17025:2017 accreditation scope for full auditor and regulatory acceptance.