What’s the most suitable electrical enclosure for the highways sector?

An electrical enclosure for the highways and motorways sector must be built to withstand a number of conditions, including extreme or adverse weather, accidental or intentional impact, vibration from high-speed traffic, intrusion, and other possible effects.

As such, the enclosure must be designed, constructed, tested and built, properly installed and maintained to defy the above factors and function in the hostile highway and motorway environment. In this article, we explore the material, IP rating and exact test specifications a highways electrical enclosure should have.

Material

The best material to construct an electrical enclosure for a highway or motorway environment is stainless steel (painted on the outside if necessary). It is tough and resistant to vandalism, forms a robust structure, is easy to weatherproof and does not corrode. In short, it promises a long and reliable life-cycle.

Contractors must be able to demonstrate that the enclosure is resistant to corrosion. The Highways Agency, in their document titled, “TR 1100 General Technical Requirements for Motorway Communications Equipment” state that this is an important requirement. This can be achieved by not only constructing the enclosure with stainless steel, but also using a “Protective Surface Treatment”, specified in TR 2180.

IP Rating

The right IP rating ensures that the electrical enclosure is constructed in such a manner that it protects against the appropriate risks of water and dust ingress. The most suitable rating for an enclosure for a highway is IP56. This means that the equipment inside the cabinet will not be exposed to any water or moisture penetration from severe wind-driven rain, or heavy splashing from passing vehicles. The right rating will also prevent dust or other small particles entering the enclosure and harming equipment.

The Highways Agency, under TR 1100, state the following IP ratings required for equipment:

  • External equipment enclosures – must be compliant with IP 56 of BS EN 60529
  • Equipment in an Outdoor Equipment Cabinet – must be compliant with IP 2X of BS EN 60529

Heating and cooling

The designer should check if the equipment to be protected by an enclosure produces heat and evaluate its ideal operating temperature, including the moisture content of the air within the enclosure.

Since the cabinet is going to be outside, it may be subjected to fluctuations in temperature – between day and night, summer and winter – that could potentially damage the equipment inside. Depending on the type of equipment being protected, the enclosure may have to be fitted with an air-conditioning (A.C.) element to prevent the inside from overheating, along with a small thermal element to protect against the cold.

TR 2130C tests

Before an electrical enclosure is used on the highway, it needs to be tested to certify that it is fit for purpose. The TR 2130C is a document published by the Highway Agency, titled “Environmental Tests for Motorway Communications Equipment and Portable and Permanent Road Traffic Control Equipment”. Within it are a set of important tests that should be carried out on all enclosures:

Temperature

There are a number of tests that analyse the temperatures that an enclosure can tolerate:

  • Dry heat – carried out in accordance with BS 7987 Class AB3 (60°C)
  • Cold – carried out in accordance with BS 7987 Class AE2 (-15°C)
  • Damp heat – carried out in accordance with BS 7987 Class AK2 (2 cycles)
  • Change of temperature – carried out as an alternative to the dry heat and cold tests
Water penetration

This test is used to evaluate how effective the enclosure is at preventing the ingress of water. Here, the IP rating will be taken into account and used as a benchmark for what the enclosure must be able to achieve. For example, a cabinet with an IP rating 54 must be able to protect against the splashing of water in all directions.

Vibration

The continuous movement of traffic on highways, along with possible transportation of the enclosure, makes the containing equipment vulnerable to the risk of vibration. The cabinet must, therefore, be tested against British Standards, BS EN 60068-2-6:2008, to evaluate any structural and mechanical weaknesses and to measure how tolerant it is to vibration.

EMC

Any equipment that emits or is susceptible to electromagnetic radiation requires this test, in accordance with BS 7987. This test will prevent the equipment being contained within the enclosure from interfering with passing by vehicles, such as ambulances and police cars.

Bump

This is a test to simulate the shocks and vibrations an enclosure may be exposed to during transportation. It will involve mounting the cabinet on a ‘Bump Table’ and ensuring the results are within prescribed limits. The test must adhere to British Standards, BS EN 60068-2-29 Test Eb.

Drop and topple

As suggested by the name, this will analyse the cabinet’s ability to protect the equipment against falls and shocks at any stage between manufacture, transportation and installation.  This should follow British Standards specification, BS EN 60068-2-31 Test R, test method Ec.

Solar radiation

This is for enclosures that may be exposed to solar radiation. If this test is carried out, the dry heat test is not needed. Similarly, solar radiation is often accounted for during the dry heat test.

Wind

According to TR 2130C, an electrical enclosure for highways and motorways should be able to withstand “without damage, wind velocities up to 46m/s from any direction”. There are three sets of tests for this, of which one must be carried out, namely; the wind tunnel test, the static loading test and a calculated justification.

Impact

Since the enclosure is going to be on the highway, it needs to be fairly robust enough to handle impact, without suffering from surface cracks, for example. The impact test, under BS 7987 will measure this quality.

Free fall

The free fall test will gauge how well the enclosure performs in protecting equipment from falls during transport. The test should simulate handling of the equipment as it would be on a real site, to measure impact in relation to each top corner and the top rear edge of the cabinet. It should be carried out in accordance with BS EN 60068-2-32 Test Ed, Procedure 1.

Exemplary cabinets

The cabinets that ICEE design especially for use in highway environments are of three types:

  1. Over parapet cabinets
  2. HADECS 600 cabinet
  3. CEC cabinets
  4. Combined 600 cabinet

As you can see, electrical enclosures, especially for such high-risk areas like the highway, need to be built in compliance with a range of specifications and thoroughly tested for performance. It’s therefore mandatory that contractors hired by project delivery heads have the capability and expertise to manage such a task adequately.

A fundamental aspect of this is the IP rating. This sets the criteria for building an enclosure that will protect equipment successfully. To understand more about IP ratings, download our free IP rating chart.