What is the clear opening of a manhole cover?
Many people often get confused when measuring the clear opening of a manhole cover.
The clear opening commonly gets mistaken for the larger visible measurement on top of the cover. To establish the clear opening size, the cover’s lid needs to be removed and the measurement of the innermost frame dimensions taken – this is the area referred to as the clear opening.
It is important that the clear opening of a cover is measured accurately, as a cover which is not large enough may not be fully supported by its framework and could fail under load. Similarly a cover which is too large may not provide adequate support and fail to meet the required loading capabilities.
See below photographs which indicate the correct and incorrect measurement of the clear opening of a manhole cover as well as the correct and incorrect way of positioning a product:
*Correct installation and measuring of a clear opening
*Incorrect installation and measuring of a clear opening
*Please note we have inserted yellow lines to clearly indicate the correct and incorrect measurements.