Detailed Product Description
The MES series current transformer belongs to the busbar-type family of instrument transformers, a category that has become the default choice for low-voltage metering in generator panels and distribution boards worldwide. Unlike wound-primary transformers that require the primary conductor to be permanently connected to the device terminals, a busbar type CT uses the actual busbar or cable passing through its window as the primary winding . This configuration offers a fundamental installation advantage: the CT can be placed around an existing conductor without disconnecting it, and the effective primary turns can be adjusted simply by routing the conductor through the window multiple times.
The toroidal core at the heart of this MES series current transformer is distinct from the laminated rectangular cores used in some competing designs. A toroidal core is formed by winding a continuous strip of grain-oriented silicon steel into a ring shape, which produces a magnetic path with a shorter mean length and fewer air gaps compared to a stacked lamination assembly . The practical consequence is improved magnetic coupling between primary and secondary circuits, reduced leakage inductance, and more consistent accuracy across the measuring range. For panel builders working with sensitive generator controllers and power meters, this translates into a secondary signal that tracks the primary current more faithfully—particularly at lower current levels where metering resolution matters.
The “MES” designation itself follows a naming convention familiar to panel builders in many markets. The series is characterized by a compact plastic housing with an integral hinged terminal cover, a feature that addresses a common installation concern: accidental contact with live secondary terminals during commissioning or maintenance . The hinged cover remains attached to the CT body, eliminating the risk of lost loose covers and providing a consistent barrier over the secondary connection points. The housing material is typically flame-retardant ABS or polycarbonate rated to V-0, which contributes to the overall safety profile of the panel assembly .
The busbar window dimensions vary by frame size within the MES series. Smaller frames such as the MES-30 accommodate a single busbar run for lower-current circuits, while larger frames like the MES-100 accept wider busbar configurations for high-current applications up to 3000A . The square or rectangular window profile is designed to match the cross-section of standard busbar stock, ensuring that the primary conductor passes through the core without contact with the insulation or core material. This clearance is important not only for dielectric integrity but also for maintaining the accuracy of the magnetic circuit—any contact or proximity between the primary conductor and the core can introduce measurement error.
Technical Specifications
| Rated test voltage |
3Kv AC (1 min) |
| Rated short-time thermal current (Ith) |
60In |
| 60In Rated dynamic current (Idyn) |
2.5Ith |
| Rated voltage (Um) |
0.72Kv AC |
| Continuous overload (Id) |
1.2In |
| Operating temperature |
-10℃ to 50℃ |
| Housing self-extinguishing class |
VO |
| Safety factor |
FS 5 |
| Secondary current |
5A/1A |
Technical Advantages
Toroidal Core for Stable Low-Current Accuracy. The continuous magnetic path of the toroidal core is particularly beneficial at the lower end of the measuring range, where metering accuracy often degrades in laminated-core designs. For generator panels monitoring light loads or standby conditions, this stability supports more reliable power readings.
Hinged Terminal Cover as a Panel Safety Feature. The permanent attachment of the terminal cover addresses a practical panel-building concern: loose covers are frequently misplaced during assembly, leaving secondary terminals exposed. The hinged design keeps the cover attached and functional throughout the panel’s service life .
Space-Efficient Housing for Dense Panels. The MES series is described by multiple sources as having a volume notably smaller than general-purpose CT models . In generator control panels where DIN rail space competes with controllers, meters, and wiring ducts, this reduced footprint allows higher component density without compromising accessibility.
Ratio Flexibility Through Primary Turns. The busbar window design allows the same CT frame to produce different ratios by varying the number of primary conductor passes. A 100/5A ratio may be achieved with one pass of a 100A conductor, or a 50/5A ratio with two passes of the same conductor. This flexibility reduces the number of distinct CT models required for a range of generator ratings.
Compliance with Recognized Standards. The MES series is designed to meet IEC 61869 (or the earlier IEC 60044-1) requirements for current transformers, with test voltages and thermal ratings aligned to these standards . For contractors and panel builders working on code-compliant installations, this alignment simplifies documentation and inspection.
Applications
Diesel Generator Control Panels. The primary application for this busbar type current transformer is current measurement in genset control and metering circuits. Generator controllers use CT inputs for load monitoring, overcurrent protection, and power calculations. The compact MES housing fits the busbar layouts typical of genset output sections.
Low-Voltage Switchgear and Distribution Boards. Panel builders integrating generator feeds into main distribution boards use MES series CTs for feeder metering and protection coordination. The range of frame sizes accommodates the variety of feeder ratings found in a typical LV switchroom .
Power Metering and Sub-Metering. Class 0.5 accuracy supports revenue-grade metering and sub-billing applications where accurate current measurement is required for cost allocation or tenant billing.
Power Factor Correction and Load Management. CTs provide the current signal for power factor controllers and load-shedding logic. The toroidal core’s stable low-current accuracy supports reliable decision-making in automated load management systems.
Retrofit and Replacement Projects. The standard MES form factor allows direct replacement of aging CTs in existing panels without modifying busbar arrangements. Distributors serving maintenance markets can stock common frame sizes for replacement demand.
FAQ
Q: What is the difference between a toroidal CT and a busbar CT?
A: The terms describe different aspects of the same device. “Toroidal” refers to the shape of the magnetic core—a continuous ring with a short magnetic path. “Busbar type” refers to the primary connection method—the primary conductor passes through the window rather than connecting to terminals . The MES series is both a toroidal core design and a busbar type CT.
Q: Can the MES series be mounted on DIN rail?
A: Yes. The MES series supports three mounting methods: busbar mounting, DIN rail mounting, and panel fixing with a metal bracket . The appropriate method depends on the panel layout and the frame size selected.
Q: How do I determine the correct ratio for my generator?
A: For a three-phase generator, calculate the rated line current from the kVA rating and system voltage. Select a CT ratio that places the normal operating current at 60–80% of the CT primary rating for optimal metering accuracy. The final selection should also account for the input range of the connected meter or controller.
Q: What does the safety factor FS 5 mean?
A: The safety factor indicates the multiple of rated primary current at which the secondary current begins to deviate from its proportional relationship. An FS of 5 means the CT maintains reasonable proportionality up to five times rated current, which is relevant for metering applications where accuracy during overload conditions is desirable .
Q: Does the MES series comply with IEC standards?
A: Yes. The series is designed to meet IEC 61869-1 and IEC 61869-2 (successor to IEC 60044-1) requirements, with test voltages and thermal ratings aligned to these standards .
Q: What maintenance does a busbar type CT require?
A: The CT has no moving parts and requires minimal maintenance. Periodic visual inspection for case damage, terminal tightness, and cleanliness is sufficient. Secondary circuits should never be opened under load, as this can generate dangerous voltages across the CT terminals.
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