Let’s start with the definition of manhole cover. It is nothing more than the cover that is placed over manholes, through which one may inspect, when necessary, what is underground (sewerage distribution networks, cable routing, aqueducts, etc.).

Manhole covers come in different shapes and materials, but when it comes to choosing which type to use, one must take into account mechanical strength, durability and the net clearance of the opening.

When we talk about mechanical strength, we are referring to the class that characterises each manhole cover. The choice depends on the area of use, which is divided into 6 groups according to the EN 124 reference standard. Each group is assigned a resistance class that must be complied with:

  • Group 1: areas that can only be used by pedestrians and cyclists. The most suitable manhole cover is class A15;
  • Group 2: pedestrian areas and similar, lay-by areas or multi-level car parks. This is the B125 class area;
  • Group 3: for gully tops installed in the area of kerbside channels of roads which, when measured from the kerb edge, extend a maximum of 0.5 m into the carriageway and a maximum of 0.2 m into the footway. This group is assigned class C250;
  • Group 4: carriageways of roads (including pedestrian streets), hard shoulders and lay-by areas, for all types of road vehicles. The class allowed by the regulations is D400;
  • Group 5: areas of imposing high wheel loads, e.g. aircraft and port pavements. The manhole cover to be used will be class E600;
  • Group 6: areas of imposing high wheel loads, e.g. aircraft pavements. The only class allowed is F900.

With regard to durability, one must consider many aspects, including the material of the manhole, the area in which it is to be installed, the temperatures and fluctuations to which it is subjected, and the frequency of traffic.

The clear opening is the diameter of the largest circle that can be inscribed in the net cross-section of the frame, basically the net clearance of the manhole. This value is normally unique for all manhole cover manufacturers. The element which is not subject to particular specifications is the outside dimension of the cover and above all the outside dimension of the frame. Therefore, each manufacturer may have different thicknesses and outside dimensions of the cover, making it impossible to interchange the covers.