Data Centre Horrors: Cable Glands and the Tale of the EMC Directive

The EMC Directive is a European regulation to enforce limitations on all electrical and electronic equipment that may cause or be affected by electromagnetic interference (EMI).

While cable glands are not directly covered by it, Technical Director at CMP Products, Lee Frizzell, says that despite them neither emitting EMI or being susceptible to it, they should be an important consideration for system designers; as without them there is scope for untold horrors on Halloween and beyond.

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The EMC (Electromagnetic Compatibility) of equipment used in the design of electrical and electronic systems is of huge importance in any installation and nowhere is that more the case than in data centres, where a power outage or equipment malfunction could be cataclysmic.

Also referred to as Radio Frequency Interference (RFI) or noise, EMI is a disturbance in the magnetic field surrounding the equipment that can affect electrical or electronic circuits in the vicinity. It is commonly generated in automation utilising drives, motors and transmitters and the problems caused by it can include over-voltage, under-voltage, or transients, all of which can lead to the degradation of the circuit.

In data centres, power sources tend to produce low-frequency EMI, which can damage hardware, corrupt data, and even wipe out an entire hard drive. Cables near EMI sources, unless properly protected, are exposed to currents, and can suffer a surge in voltage. It is the high-voltage current that then generates electrical noise, which interferes with data and voice applications that the cabling supports.

Because there are so many different types of data centre, the Uptime Institute in the US developed the Tier Standard, which the UK and most of the world have adopted. This evaluates the quality and reliability of data centres and provides guidance on the level of EMI protection needed.

Hewlett Packard outlines the tiers like this:

• Tier 1: Has a single path for power and cooling and few, if any, redundant and backup components. It has an expected uptime of 99.671% (28.8 hours of downtime annually).
• Tier 2: Has a single path for power and cooling and some redundant and backup components. It has an expected uptime of 99.741% (22 hours of downtime annually).
• Tier 3:Has multiple paths for power and cooling and systems in place to update and maintain it without taking it offline. It has an expected uptime of 99.982% (1.6 hours of downtime annually).
• Tier 4: Built to be completely fault tolerant and has redundancy for every component. It has an expected uptime of 99.995% (26.3 minutes of downtime annually).

Each tier contains the required components of all the tiers below it, with design rules coming into play for Tiers 3 and 4 to address potential threats to uptime of the systems.

Protection Against EMI

Shielding is proven as the best protection against EMI and is of the greatest importance in higher-tier data centres. This is the practice of surrounding electronics and cables with conductive or magnetic materials, which protect against incoming or outgoing emissions of electromagnetic frequencies.

Legislative safety standards and directives have long been established to ensure that the environment, equipment, and machinery are properly shielded, with the key initiative being the European Union EMC Directive. Originally enacted in 1989 under the Directive 89/336/EEC, the EMC Directive has witnessed significant development since it first came into force. It has been amended several times since then; the latest being in 2016, when the new EMC 2014/30/EU Directive became effective.

The EMC Directive requires that products must not generate unwanted electromagnetic pollution or interference and that products must be immune to a reasonable amount of noise pollution or interference. EMC testing is required to be carried out on any electrical or electronic product that may either cause electromagnetic radiation or be affected by it.

The directive means equipment manufacturers must make considerations early in the electrical and electronic design process to ensure the equipment will pass EMC test requirements. Many design techniques are therefore adopted to limit EMI emissions at source or to protect susceptible equipment. Circuits may be partitioned, segregating EMC critical and non-critical areas. A good grounding scheme may be implemented, preventing earth loops from leading to unwanted signals being radiated. Shielded cables and enclosures are often utilised, providing barriers to unwanted radiated noise.

A Common Oversight in Cable Management

However, a significant oversight is often found at the point of cable entry into an electrical enclosure. By adding openings in enclosures, pathways are created to allow noise to breach the shielded enclosure. Unterminated or poorly terminated cable shields can allow noise to be carried into the enclosures, acting as antennas to radiate noise onto sensitive circuits.

Grounding the cable shield effectively inside a cable gland at the point of entry eliminates a potential noise pathway and reduces the risks of radiated emissions being carried into the enclosure.

Cable glands, which employ a robust 360-degree circumferential termination of the cable screen, shield braid or armour (e.g. with a cone and clamping ring, or a dedicated continuity device) in their metallic body, contribute to the electromagnetic compatibility of installations through reliable low impedance connections. Stats that are backed up by a number of industry studies into the role they can play in EMC protection.

One such independent study was commissioned by ourselves in 2021 and carried out by a third party, Eurofins E&E. 3 Metre Class B Radiated Emission Measurement tests were carried out in accordance with EN 55032, to gauge the performance of cable glands terminated onto screened, braid shielded and armoured cables. The results proved categorically that using a reliable, 360-degree termination of the shield or metallic cable layer inside the cable gland improved noise attenuation throughout the frequency range.

When it comes to avoiding data centre horrors and improving electrical safety, whether it be with the intention of protecting people, power supplies or data, it is imperative that every potential step is taken to ensure the systems are the most robust they possibly can be. As such, suitably proven cable glands need to be given proper consideration and if this can be done within the remit of the EMC Directive then it would ensure they always are and that everyone can sleep easy!