Equipment enclosures

Today, more and more electronic and processor-based equipment is located trackside and on platforms for signalling, telecoms, electrification control, and asset monitoring. Even platforms on small stations may have customer information and video surveillance systems, which need somewhere to locate and protect the expensive equipment. Equipment rooms are expensive, and carefully designed enclosures are required to protect essential equipment for a safe and reliable railway.

The requirements and challenges associated with equipment enclosures include providing optimal thermal performance, protection against environmental influences, security and anti-theft protection, accessibility, scalability, flexibility, and cost. Equipment enclosures will be exposed to a wide range of environmental influences such as heat, cold, humidity, dust, and vandalism. They must also comply with standards and be approved to ensure protection against mechanical shock, vibration, and EMC protection.

Many years ago, trackside equipment was installed in custom made brick and mortar buildings and, as many contained relays, they were known as relay rooms. Cabinets made of wood or metal were also typically used for cable terminations or relays and were known as ‘location cases’ or simply ‘locs’.

Relocatable Equipment Buildings

The next development in equipment enclosures was the introduction of modular Relocatable Equipment Buildings (REBs). ‘Relocatable’ is a misnomer as once installed trackside they are not often relocated. Rather, they are built up at a supplier’s factory, before being ‘relocated’ to site.

First introduced over 30 years ago, the ubiquitous REB has become a familiar item of trackside equipment. An REB is not perfect though. Being typically constructed of light weight material they are not very well insulated. It is not unknown in winter for a visiting technician to turn the heating thermostat up and forget to reset it when leaving. They then return to the REB in the height of summer to find the REB is a sauna, which is not good even for passive equipment. REBs also require a substantial base and lifting equipment to install into position.

The traditional metal trackside railway loc also has poor thermal performance. Measures to protect against heat include providing ‘hoods’ above the loc or painting them white, with a heater for use in winter. Many were only provided with front access, which is also not ideal for modern electronic equipment.

REBs provide a safe place to work and shelter, but they are expensive. In the telecoms industry, active electronic and processor-based equipment is often located in equipment enclosures and REBs are not used. In the rail industry, similar modern electronic processor-based control and communications equipment has also been introduced, which is more distributed, requires less space, and is more reliable than previous systems. The maintenance requirements are also much reduced which means trackside equipment can now be housed in carefully designed equipment enclosures, rather than REBs or the traditional loc.

Requirements and challenges

Trains travelling at speed cause high turbulence and vibrations, and trackside equipment enclosures will be subject to many environmental influences. Properly designed equipment enclosures add value by significantly reducing total cost of ownership and operational costs. They also improve safety by increasing reliability and service life. Safe access to the enclosure can be provided with installation 90 degrees to the railway track and by providing a fence to maintain a safe distance.  

The issue of cooling is important when anything is installed outdoors. Not only must the power loss of the installed equipment be dissipated, but daily and seasonal outside temperatures must also be managed. The thermal output of the cabinet must ensure an operating temperature appropriate to the equipment in extreme ambient temperatures. This provides greater reliability and extends the service life of the asset.

Natural or ‘free’ convection for heat dissipation is the first option and a thermal output of several hundred Watts can typically be dissipated by natural convection. When this reaches its limit, a forced type of convection cooling may be required and speed-controlled, air-filtered fans with thermostats are the next option.

The air supplied via air-filtered fans must be adapted to the air requirements of the components. Typically, filter mats will be required to protect the interior of the cabinet from dust, but they will require maintenance. Direct air cooling can be reliable though, with a long service life and low energy consumption. Air-conditioning cooling units offer the highest cooling capacity and enable cooling of the cabinet interior independent of the ambient temperature, but they require maintenance and servicing and will need a power source.
Protection against unwanted electromagnetic radiation on sensitive electronics must be provided and appropriate measures for grounding and lightning protection are also necessary.

A high degree of robustness and stability are required to address the risk of vandalism and unauthorised access. Therefore, it is important that door handles are protected and that screws for removing the roof, side walls, and base panels are only accessible from the inside, making unauthorised access to the interior of the cabinet considerably more difficult.

To ensure that only fit-for-purpose trackside equipment enclosures are used, Network Rail has introduced specification NR/L2/SIG/19820/K02 Equipment Enclosures. This was issued in March 2022 and is mandatory, with compliance from 4 June 2022.

NR/L2/SIG/10920/K02

The specification sets out the technical requirements and covers two standard equipment enclosure external sizes of 700mm x 700mm and 1300mm x 700mm, (both 2000mm high). There are three types of environmental control: passive (default), forced air, and air-conditioned. Additionally, there are two security levels: standard security (LPS 1175 SR2) and high security (LPS 1175 SR3). The equipment enclosure shall also be designed and manufactured to have a minimum operational service life of 35 years, and to be visited and opened a minimum of once every 13 weeks, in addition to any faulting activities.

LPS stands for Loss Prevention Standard and LPS 1175 is published by the Loss Prevention Certification Board. The SR2 security rating provides resistance to attempts at forced entry, using bodily physical force and a range of hand tools, including those that create noise for a maximum attack time of three minutes over 15 minutes duration. SR3 provides moderate resistance to determined attempts with a wide range of hand tools with a more significant mechanical advantage, including those that create noise for a maximum attack time of five minutes over 20 minutes duration.

The equipment enclosures must be developed and designed in compliance with NR/L2/RSE/0005 Design for Reliability. This process integrates a series of tools and methodologies into a supplier’s existing design processes to create documented, traceable, and controlled evidence of reliability, availability, and maintainability.

The Mean Time Between Failure (MTBF) of the climate control system must exceed 100,000 hours, and the Mean Active Repair Time (MART) for removing and replacing the entire outer shroud must be two hours or less. Each Line Replaceable Unit (LRU) must have a MART of one hour or less, and it should be possible to replace any of the LRUs with the encloser in situ. This includes the doors.
The specification also covers the requirements for: lifting; operating environment; environmental testing; Electromagnetic Compatibility (EMC) and Electromagnetic Induction (EMI); accessories such as documentation holders; labelling; solar radiation; earthing; and installation and maintenance.

Conclusion

There may be some railway asset managers and maintainers who prefer the traditional REB to protect equipment and as a covered location to maintain it. However, other industries have successfully moved to locating reliable and expensive electronic equipment in enclosures, and the rail industry cannot afford not to do the same. Network Rail has produced a specification for equipment enclosures, and several suppliers have already successfully designed and obtained product approval for some excellent products.