A slip ring is an electromechanical device that transfers electrical power or signals from a stationary structure to a rotating or oscillating one. It solves a fundamental problem in electrical engineering: how to maintain a continuous electrical connection between two parts when one of them is moving.
Without a slip ring, any rotating machine that needs a live electrical connection would be limited by the cable attached to it. The cable would wind up and eventually break as the machine turned. Slip rings eliminate that constraint, allowing unlimited rotation while maintaining an uninterrupted electrical circuit.
Metreel is a leading UK supplier of slip rings for industrial material handling applications.
In this post, we’re here to explain more about slip rings, including what they are and how they work.
How Does A Slip Ring Work?
A slip ring assembly consists of two main components: a set of conductive rings and a set of brushes. The rings are mounted to the rotating part of the machine and turn with it. The brushes are fixed to the stationary housing and maintain constant contact with the surface of each ring as it rotates.
Each ring carries a separate electrical circuit. As the assembly turns, the brushes slide along the surface of the rings, maintaining electrical contact throughout the rotation. This is what gives slip rings their alternative name: rotary electrical connectors. The term collector ring is also used, particularly in heavy industrial contexts.
The brushes are typically made from copper graphite, which combines good electrical conductivity with low friction and acceptable wear characteristics. For applications where low contact resistance and minimal electrical noise are critical, such as communication circuits and PLC connections, silver-plated rings with silver graphite brushes can be specified instead. Gold plating is also available for the highest-sensitivity applications.
What Are Slip Rings Used For?
Slip rings are found in any application where a rotating part needs a continuous supply of power or control signals. Common examples include:
- Cranes and hoists, where the rotating hook block or slewing mechanism needs power
- Reeling drums, where the drum rotates to wind and unwind cable while the electrical connection remains live
- Wind turbines, where the nacelle rotates relative to the tower
- Rotary tables are used in manufacturing, where the workpiece turns during machining or assembly
- Medical imaging equipment, including CT scanners
In industrial material handling specifically, slip rings are a core component of reeling drum systems. The drum itself rotates as cable is paid out or retrieved and the slip ring inside it ensures the electrical circuit to the connected equipment stays live throughout that movement.
Collector Columns And Slip Ring Assemblies
In overhead crane and gantry applications, slip rings are often incorporated into a collector column. A collector column is a vertical assembly that mounts to the rotating or oscillating part of the equipment and houses the slip rings within a weatherproof enclosure. The column transfers multiple power and control functions simultaneously, with each ring in the assembly carrying a separate circuit.
Metreel manufactures a comprehensive range of collector columns and slip ring assemblies, covering everything from standard configurations to bespoke designs for specialist environments. The range includes:
- CSS columns for low to medium current at low voltage
- CL and CXL columns for low to high current at low to medium voltage, with capacity for a large number of rings
- Heavy duty and extra heavy duty versions capable of up to 600 amps and voltages of up to 12,000 volts
All Metreel collector columns are built as weatherproof units with IP65-rated enclosures and sealed-for-life bearings, suitable for continuous rotation in demanding industrial environments. The brush gear on larger units uses a split-clamp construction that allows easy removal and replacement without dismantling the wider assembly.
Where applications require more than standard electrical power transfer, Metreel’s collector columns can also incorporate rotary couplings for oil or air supply, as well as fibre optic couplers and mercury transmitters for specialist signal transmission requirements.
Slip Rings Versus Other Powerfeed Methods
Slip rings are one of several ways to deliver power to moving equipment. Understanding when to use them rather than an alternative is important for specifying the right system.
Festoon cable systems suspend cables from a series of trolleys along a track, allowing the cable to travel horizontally with the equipment. They suit linear travel applications such as bridge cranes running on a runway, but are not suitable where the equipment rotates, because the cable would wind up and fail.
Steel drag chains guide and protect cables during linear reciprocating motion. Like festoons, they handle linear travel well but cannot accommodate continuous rotation.
Slip rings and collector columns are the correct choice wherever the equipment rotates or oscillates rather than travels in a straight line. They are also the right solution inside reeling drums, where the drum must be free to rotate while the electrical connection at the core of the drum stays live.
For a broader overview of how these systems fit together in crane and handling applications, the Metreel guide to crane electrification systems covers the full range of powerfeed options and how to choose between them.
Maintenance And Inspection
Slip rings require periodic inspection and maintenance to perform reliably over their service life. The main wear components are the brushes, which gradually wear down through contact with the rotating rings. The rate of wear depends on the current load, rotational speed and operating environment.
Metreel’s collector columns are designed to make this maintenance as straightforward as possible. The brush gear on the larger CL and CXL units can be removed without specialist tools thanks to the split-clamp construction of the mounting brackets. All units have removable covers to allow access for inspection without full disassembly.
As with all lifting and handling equipment, slip rings and collector columns used in crane applications fall within the scope of LOLER (Lifting Operations and Lifting Equipment Regulations 1998) and PUWER (Provision and Use of Work Equipment Regulations 1998), both of which require regular thorough examination by a competent person.
Slip Rings & Collector Columns From Metreel
Metreel is a UK manufacturer and supplier of collector columns and slip ring assemblies for industrial material handling applications.
Our vast powerfeed range covers reeling drums, festoons, conductor systems, drag chains and electrical control equipment alongside collector columns and slip rings. All of which gives specifiers a single source for the complete powerfeed system.
To discuss your requirements or get a quote, contact the Metreel team on 0115 932 7010 or send us a message get in touch.