What Is RoHS, and Why Does It Matter?

RoHS stands for the Restriction of Hazardous Substances, a regulation introduced by the European Union to reduce harmful materials in electrical and electronic equipment. It limits the use of 10 substances (below):

• Lead (Pb)
• Cadmium (Cd)
• Mercury (Hg)
• Hexavalent chromium (Cr⁶⁺)
• Two flame retardants (PBB, PBDE)
• Four phthalates (DEHP, BBP, DBP, DIBP)

Can Mercury Slip Rings be Used in RoHS Compliant Applications?

Clearing Up the Confusion

Mercury and RoHS compliance often seem incompatible—but the reality is more nuanced. Many engineers and buyers mistakenly assume that any product containing elemental mercury is automatically non-compliant with the RoHS Directive. That’s not always the case.

The short answer? Yes—mercury slip rings can be used in equipment and applications where RoHS compliance is required. Meridian Laboratory has worked with numerous customers across the world to navigate this question and understand when and how mercury-containing slip rings can be used while remaining RoHS compliant.

Here’s what you need to know:
RoHS regulations do restrict the use of mercury—but they also include a variety of exemptions. Slip rings are one such exemption when designed and used under defined conditions outlined in the RoHS Directive.

Exempt but Essential: Understanding the Use of Mercury in Slip Rings

Slip rings are electromechanical components that transfer power and signals between stationary and rotating systems. In certain industries, mercury-based slip rings remain the best—or only—solution for applications that require ultra-low electrical resistance, zero signal loss, and long-term reliability under continuous rotation.

To account for this, RoHS includes Annex III Exemption 4(f), which permits:

“Mercury in other electrical and electronic applications not specifically mentioned in this Annex.”

This exemption recognizes that some technologies, like mercury-based slip rings, are still necessary in equipment for it to perform at the levels they are required to.

Examples of where mercury slip rings are essential include:

• Aerospace and defense systems
• High-end medical equipment (e.g., CT scanners)
• Industrial automation and robotics
• Semiconductor and electronics manufacturing
• Oil and gas exploration
• Rotary test equipment and scientific instrumentation
  

Additionally, Article 2, Section 4 of the RoHS Directive provides a variety of exemptions for components like slip rings containing elemental mercury when they are part of a larger piece of equipment that is not otherwise covered by the Directive.

This exemption exists because the RoHS Directive primarily targets the restriction of hazardous substances in electrical and electronic equipment that is mass-produced and widely distributed within consumer-facing products (fluorescent lamps, thermostats, thermometers, batteries, etc.).

In contrast, slip rings that contain mercury are typically used in highly specialized, often custom-built equipment. These devices are not standalone consumer products but integral components of complex systems like:

• Medical imaging equipment
• Aerospace instrumentation
• High-precision defense systems
• Semiconductor Manufacturing

—where no viable alternative currently offers equivalent performance.

Article 2 – Scope of the RoHS Directive

1. This Directive shall, subject to paragraph 2, apply to EEE (Electrical and Electronic Equipment) falling within the categories set out in Annex I.
2. Without prejudice to Article 4(3) and 4(4), Member States shall provide that EEE that was outside the scope of Directive 2002/95/EC, but which would not comply with this Directive, may nevertheless continue to be made available on the market until 22 July 2019.
3. This Directive shall apply without prejudice to the requirements of Union legislation on safety and health, and on chemicals, in particular Regulation (EC) No 1907/2006, as well as the requirements of specific Union waste management legislation.
4. This Directive does not apply to:(a) Equipment necessary for the protection of the essential interests of the security of Member States, including arms, munitions, and war material intended for specifically military purposes
(b) Equipment designed to be sent into space
(c) Equipment specifically designed to be installed as part of another type of equipment that is excluded or not within the scope of this Directive
(d) Large-scale stationary industrial tools
(e) Large-scale fixed installations
(f) Means of transport for persons or goods, excluding electric two-wheel vehicles which are not type-approved
(g) Non-road mobile machinery made available exclusively for professional use
(h) Active implantable medical devices
(i) Photovoltaic panels intended for permanent use at a defined location
(j) Equipment specifically designed solely for R&D purposes and made available on a B2B basis

Meridian Laboratory’s Approach to RoHS and Mercury-Free Innovation

Meridian Laboratory is committed to supporting both current needs and future-focused innovation. While some of our slip ring models still utilize elemental mercury, we are actively engineering, designing, and testing new mercury-free models across our product line.

Our ROTOCON® brushless slip rings already deliver industry-leading performance without mercury in many standard configurations—offering maintenance-free, low-resistance, and high-reliability solutions for rotating power and signal transmission.

The Bottom Line: Confidence and Compliance

Slip rings which contain elemental mercury can still be used in applications aligned with RoHS compliance—thanks to specific, well-established exemptions that apply to the specialized and technically demanding use cases in which they are required.

These exemptions are legal, documented provisions built into the RoHS Directive to ensure essential technologies can continue to function safely and effectively.

Whether you’re sourcing for a legacy system or developing next-generation equipment, our team is ready to help you choose the right slip ring—with full confidence in:

Have questions?

We’re here to help. Reach out to Meridian Laboratory for guidance on RoHS compliance and slip ring selection tailored to your needs.