Shunt resistors are important sensing components for current sampling in electricity meters. They utilize the low resistance characteristics of manganese-copper alloy to achieve accurate current measurement by measuring the voltage drop across the resistor when current flows through it (Ohm's Law V=I×R). They are also a low-cost and highly adaptable sampling solution in electricity meters.
Currently, the industry primarily classifies electricity meter shunt resistors based on welding process, installation method, structural specifications, and accuracy level. Different types exhibit significant differences in process, performance, and applicable scenarios, and all must comply with national/industry standards such as JB/T 11722-2013 and DL/T 2345-2021.
Classified by welding process: brazed shunt vs. electron beam welded shunt
This is a classification of electricity meter shunts based on their manufacturing process, which determines the product's reliability, accuracy, and temperature adaptability. Electron beam welding is a new technology that is currently replacing traditional brazing methods.
Brazed Shunt
1. Process Features
Connected by brazing the manganin resistance sheet to the copper terminal using traditional brazing materials, the process is simple and has low manufacturing costs.
2. Core Characteristics
There is a problem of heat generation in the brazing layer. The manganin and copper terminal tend to separate due to thermal expansion and contraction, resulting in a relatively high temperature coefficient, average resistance stability, and weak anti-lightning strike capability.
3. Application Scenarios
General electricity meters and economical electricity meters with low requirements for measurement accuracy.
Electron Beam Welded Shunt
1. Process Features
No brazing materials are used. The manganin and copper terminal are fused into one piece via high-temperature electron beam. It has extremely high requirements for the purity of manganin and copper materials, with strict process precision.
2. Core Characteristics
It has a low temperature coefficient, almost no resistance drift, and no additional heat generation from brazing materials. The manganin and copper terminal never separate. It can easily adapt to Class 0.5 electricity meters, pass the 3000A/10ms lightning strike test, and has stronger oxidation resistance and overload capacity.
3. Application Scenarios
Medium and high-power DC electricity meters (charging piles, photovoltaics), industrial-grade electricity meters, and outdoor electricity meters in wide-temperature environments. It is also the mainstream choice for integrated DC electricity meter shunts currently.
Classified by installation method: built-in integrated shunt vs. external separate shunt
This classification primarily targets DC energy meters (especially for electric vehicle charging stations). The core difference lies in whether the shunt resistor is integrated with the energy meter body, which directly affects the meter's installation, power consumption, anti-interference capability, and overall measurement error. This is also a key consideration when selecting energy meters for charging stations.
External Split-type Shunt
1. Structural Features
The shunt is independent of the electricity meter body and needs to be connected to the meter via sampling wires. Separate installation space and wiring routes must be planned.
2. Core Characteristics
To reduce long-distance sampling interference, high-voltage signal transmission (75mV/50mV) is mostly adopted, resulting in significantly higher power consumption and heat generation (power consumption reaches 22.5VA under 300A working condition). Measurement errors are superimposed by the meter, shunt, and wiring process, leading to high total error uncertainty (for a conventional Class 1.0 meter + Class 0.5 shunt, the total error can reach ±1.5%). It has weak anti-electromagnetic interference capability.
3. Application Scenarios
Early DC charging pile electricity meters, dual-gun DC charging piles, and energy storage metering scenarios with low requirements for installation space.
Built-in Integrated Shunt
1. Structural Features
The shunt is directly integrated inside the electricity meter body, with no external sampling wires required. Only external voltage lines and communication lines are needed, making wiring extremely simple.
2. Core Characteristics
It adopts low-voltage signal transmission (6mV). The shunt has a smaller resistance value, and its power consumption is only 1/12 of that of the split-type (merely 1.8VA under 300A working condition), featuring low heat generation and controllable temperature rise. The sampling link is short and closed, with no additional error superposition, and the measurement accuracy can reach Class 0.5 (error ±0.5%). It has strong anti-interference capability and can also realize integrated lead sealing to prevent tampering.
3. Application Scenarios
New single-gun DC charging pile electricity meters, high-precision photovoltaic electricity meters, and compact on-vehicle/small energy storage electricity meters. It is the technological evolution direction of DC electricity meters.
3. Applicable scenarios: The new single-gun DC charging pile energy meter, high-precision photovoltaic metering energy meter, and compact on-board/small-scale energy storage energy meter represent the direction of technological advancement for DC energy meters.
Classified by structural specifications: Standard FL series current shunts
This is a common structural model of a DC power meter shunt. The core components are divided into the FL-2 basic type and the FL-29/FL-39 high-power type, both featuring a four-terminal structure (outer current terminals and inner potential terminals), suitable for different current ranges and output voltages.
1.FL-2 Type: Basic mainstream model, accuracy class 0.5/1.0, current range 1A~15000A, rated output voltage options include 20mV, 30mV, 50mV, 75mV, 100mV (75mV is standard), temperature rise ≤80℃ below 50A, and ≤120℃ above 50A. Suitable for most AC energy meters and small to medium power DC energy meters;
2.FL-29/FL-39 Type: An improved high-power version of the FL-2, designed for ultra-high current applications above 2000A. It features a high-temperature resistant insulated base and stronger overload capacity, suitable for industrial ultra-high power DC metering applications;
3.General Features: All models use manganese-copper alloy resistance sheets + copper connectors, support customized dimensions, and some manufacturers can provide special specifications for export, adapting to different national energy meter standards.
Classified by accuracy level: 0.2 class / 0.5 class / 1 class shunts
This classification is based on the DL/T 2345-2021 standard for external shunts of DC energy meters. The accuracy class directly corresponds to the metering accuracy of the energy meter and is also a core indicator for the factory inspection of the shunt.
Basic Error Limits of Shunt Resistors
| Load Current (I) | Measurement Condition | Class 0.2 | Class 0.5 | Class 1 |
|---|---|---|---|---|
| 0.01 Iₙ ≤ I ≤ 0.05 Iₙ | After thermal stabilization of the shunt resistor | ±0.4% | ±1% | ±2% |
| 0.05 Iₙ ≤ I ≤ 1.2 Iₙ | After thermal stabilization of the shunt resistor | ±0.2% | ±0.5% | ±1% |
1.Class 0.2 Shunt
The highest precision class with minimal basic error under reference conditions. The impact of temperature and humidity variations on errors is strictly controlled. Applications: Laboratory calibration, high-precision industrial metering electricity meters, and customs clearance metering electricity meters.
2.Class 0.5 Shunt
The mainstream precision class in the industry. Applications: Civil/industrial AC electricity meters, DC charging pile electricity meters, and photovoltaic metering electricity meters. It is also the standard precision for the FL series shunts.
3.Class 1 Shunt
A cost-effective precision class. Applications: High-current metering above 5000A, power grid electricity meters with low precision requirements, and temporary metering electricity meters.
Comparison Table of Core Types for Electricity Meter Shunts
To more clearly illustrate the differences between different types, the following compares four core shunt resistors-brazed/electron beam welded (process) and internal/external (installation)-which are the most commonly used in the industry, based on their key performance indicators.
| Comparison Dimension | Manganin Wire Shunt | Electron-Beam Welded Shunt | External Discrete Type | Internal Integrated Type |
|---|---|---|---|---|
| Temperature Coefficient | > 50 ppm | < 30 ppm | - | - |
| 300 A Power Dissipation (Example) | - | - | 22.5 VA | 1.8 VA |
| Metering Accuracy Error | ±1% ~ ±2% | ±0.5% ~ ±1% | ±1.5% (cumulative) | ±0.5% (non-cumulative) |
| Anti-Interference Capability | Average | Strong | Weak (long sampling leads) | Strong (sealed signal loop) |
| Manufacturing Cost | Low | Medium–High | Low (system-level solution) | Medium (integrated solution) |
| Typical Application Scenarios | General residential energy meters | Industrial / DC / wide-temperature energy meters | Dual-gun DC fast-charging energy meters | DC fast-charging / photovoltaic energy meters |