Mercotac® Learning Center

Electrical Characteristics

Learning Center Electrical Characteristics

What engineers need to know about the electrical characteristics of Mercotac brushless slip rings.

Also check out:

Learning Center – Construction & Materials

Learning Center – Rotational Characteristics

Frequently Asked Questions

Technical Info.

The purpose of the Electrical Characteristics page is to provide guidance to engineers who are interested in using our brushless slip ring technology in their machine design. The page details the fundamental design principles that engineers should be aware of when incorporating our technology into their projects, including information on voltage, current, resistance, and signal integrity. By providing this information, we aim to help engineers optimize their designs and ensure the proper function and reliability of their machines.

Learn about Mercotac® Brushless Slip Ring Electrical Characteristics

To ensure optimal performance and avoid potential issues, it is crucial to make proper and secure connections for both power and signal wires to the terminals of the Mercotac® Brushless Slip Rings. Using undersized wires or poor connections may generate additional heat, reduce signal quality, and ultimately lead to unit failure. The maximum temperature specification for the Mercotac unit in the application should also be taken into consideration, as it depends on various factors such as ambient temperature, rotational speed, and electrical current. To achieve the best connections, it is recommended to use the recommended disconnects, especially for high current applications. It's important to note that soldering to the tabs of a Mercotac should be avoided, as it will cause overheating, unit failure, and will void the warranty.

The voltage rating for a Mercotac Brushless Slip Ring is the maximum electrical voltage in either alternating current (VAC) or direct current (VDC) that it can be operated at. If the voltage rating is exceeded, the higher voltage can overcome the insulation and jump between circuits resulting in an electrical short or failure of the Mercotac.

However, it's important to note that single conductor models do not have a voltage rating (listed as Not Applicable or N/A) since they only have one circuit and the Mercotac Brushless Slip Ring is analogous to a very large gauge single wire. Therefore, a single conductor Mercotac is able to handle high voltages, and the electrical performance is only limited by the amount of current that passes through the unit. It's essential to keep in mind that on single channel models, the body is not insulated from the conductor. Please refer to the following Current Rating section for more information.

The current rating of a Mercotac Brushless Slip Ring refers to the maximum amount of electrical current, measured in amps, that the unit can safely handle. Operating the unit beyond its current rating may result in excessive heat generation and overheating, leading to potential issues or failure. It's important to note that the maximum current rating is specified at room temperature and may decrease in high ambient temperature conditions, as well as due to heat generated by rotation or through conduction from the Mercotac mounting or connections.

For high current applications, it's crucial to use the recommended disconnects as they have a higher current rating due to their design and a more secure crimp, both of which generate less heat. It's also recommended to use a fuse to prevent exceeding the current rating. We provide a wire size and maximum current rating table under the Connections section to help guide proper wire sizing and prevent overloading.

Please refer to the Operating Temperature section for further details regarding overheating.

Allowable Ampacity*
AWG Max. Current Carrying
Capacity (Amps)
10 30
12 20
14 15
16 12
18 9
20 7
22 5

*This chart is provided solely for informational purposes. The values presented in this table are derived from single insulated wires operating in free air at a temperature of 25°C (77°F). The ampacity needs to be adjusted or derated for multi-conductor cables in order to account for the heat generated by increased current flow and to ensure proper heat dissipation. Additionally, follow all electrical regulatory guidelines for your geography.

Contact resistance is the measurement of the electrical resistance (or the opposition to electrical current flow) through a rotating Mercotac Brushless Slip Ring. The lower the contact resistance is, the better an electrical connection is since there is less electrical energy loss through heat. Due to the unique design and the use of liquid metal, Mercotac Brushless Slip Rings have a resistance of less than one milliohm at the rotating contact interface. Due to the similar materials and design used across all models, contact resistance is very low and is the same regardless of the model.

Contact resistance is often important with applications involving data and signal transfer. Lower contact resistance translates into minimal signal degradation and better transfer through the connector. Also contact resistance is just as important in high current applications as a lower contact resistance will generate less heat.

With traditional slip rings, the resistance starts out much higher than a Mercotac Brushless Slip Ring and this can increase and vary as the brush-type slip rings degrades over time. The variation can cause noise in the electrical signal and could impact sensitive signals. This is due to the physical rubbing of the brushes against the rings which creates wear on both parts and generates dust. Mercotac Brushless Slip Rings do not rely on physical contact between rotating parts so they do not wear like a traditional slip ring and they do not generate dust.

Thermocouple applications require a one-time initial calibration for the dissimilar metals in the circuit through the Mercotac Brushless Slip Ring, and thereafter the thermocouple readings will be steady, reliable, and accurate.

Circuit separation refers to the degree to which individual circuits are electrically isolated from one another in a Mercotac Brushless Slip Ring. A higher circuit separation rating (measured in ohms) indicates better insulation. Mercotac Brushless Slip Rings have a minimum circuit separation rating of 25 Megohms, and the actual insulation resistance is typically even higher. Models with only one conductor do not have a circuit separation rating and are listed as "Not Applicable" (N/A) since they have only one circuit and do not require circuit separation. Please note that in single-channel models, the body is not insulated from the conductor.

Mercotac Brushless Slip Rings have a specific operating temperature range (in degrees Fahrenheit or Celsius) for each model. Generally, the temperature range is -20°F to 140°F, but certain models have a lower temperature rating of only 45°F. At lower temperatures, the rotational torque may increase due to the thickening of the fluids. At temperatures above the recommended range, internal parts can deform or melt, causing failure or, in the worst case, the Mercotac to come apart.

If overheating is an issue, it is usually caused by heat transfer through a roller or shaft, an overcurrent condition, poor connections, or using too small a wire for the current. To address heat transfer from a heated source, the Mercotac Brushless Slip Ring can be thermally isolated with insulating materials or cooled with forced air, fins, and/or cooling coils. For overcurrent conditions, the current may need to be verified, since any current above the rating for the Mercotac Brushless Slip Ring can generate additional internal heat. In this case, the current will need to be reduced, and it could be compensated with an increase in voltage or using a different model with a higher current rating.

It is essential to properly and fully connect power and signal wires to the terminals of the Mercotac Brushless Slip Ring. Poor connections may generate additional heat. The combination of ambient temperature, rotational speed/friction, current power, and (poor) connection quality to the Mercotac Brushless Slip Ring should be limited by the maximum temperature specification for the unit in the application.

It is very important to keep the operating temperature of the Mercotac slip ring below 140°F (60°C) as measured on the body. Electrical current heat rise, rotational heat rise, and the ambient temperature are factors contributing to the operating temperature of the Mercotac.

The following data is from a model 430. Depending on your operating conditions it may not be directly applicable to your application.


Typical Rotational Temperature Rise
RPM Temp
500 RPM 9.5°C
1200 RPM 15°C


Typical Electrical Current Temperature Rise °C at 208 VAC*
Amps Wire Gauge Channel 1,2
Channel 3,4
4 Amps 18 AWG 1°C -
5 Amps 18 AWG N/A -
10 Amps 16 AWG N/A 2°C
20 Amps 12 AWG N/A 4°C
30 Amps 10 AWG N/A 9°C

*Test Conditions: Room Temperature, Using Mercotac supplied disconnects and a single insulated wire

Power, or the rate of energy transfer, is often measured in Watts, which is the unit of measure for power. The electrical calculation of power is defined as the voltage (in volts) multiplied by the current (in amps). When selecting a Mercotac Brushless Slip Ring for an application, a Wattage specification does not directly apply, but the voltage and current ratings are important considerations. If more power is needed, it is recommended to increase the voltage (within the maximum voltage rating) rather than the current, as raising the voltage will not generate more heat in the Mercotac, while increasing the current will. Please refer to the Voltage and Current Rating sections above for more information.

For data transfer in communication systems (CAN BUS, Cat-5 Ethernet, etc.), frequency rating is important since it indicates communication speed, usually specified as bit rate. The frequency of a signal voltage is measured in cycles per second (or hertz). Most data communication systems operate in the Megabit range (MHz), which is millions of bits per second, although there are newer Ethernet standards that operate in the Gigabit range.

The maximum frequency specification is typically important for applications where data or signals will be transferred through the Mercotac Brushless Slip Ring. If the frequency of the application exceeds the rated frequency for Mercotac Brushless Slip Rings, the signal will be degraded or may not pass through the Mercotac at all. As a general rule of thumb, digital signals require more bandwidth than analog signals since they are square waves composed of very high frequencies. To use Mercotac Brushless Slip Rings for digital signals, one would derate the maximum Mercotac frequency by dividing it by at least 3 to get the maximum permissible digital frequency.

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