Traditionally, most precast trench is placed in the ground with concrete lids that protect the electrical cable from the elements or from future excavation. One issue that arises when burying electrical cable in this fashion is that you essentially trap the heat generated by the cables as electrical currents pass through them.
This heat makes it necessary to derate the cables to minimize the heat created, but doing so makes it necessary to use more cable than required without derating, and therefore you are left with a higher cost (especially when considering the price of copper today and the fact that electrical cable is made up largely of copper). Until now, the solution to this issue was to use a steel grated lid on top of the trench as opposed to the concrete lid, but this creates problems of its own. Grated lids means that dirt and debris can fall into the trench making it dangerous especially when cleaning. To do so safely means powering down the whole system before cleaning the trench out.
Thanks to a customer of ours, a new solution exists that allows the cable to be used to its full capacity and no grated lids means no unwanted debris falling into the trench.
United Wire from Richmond Hill, ON is in the process of patenting their venting idea using offset trenches in a vertical fashion to allow free air to flow through the trench even with the standard, less expensive, concrete lids. The idea means that we create trenches made special for them that has screens in the side of the trench at the location where the vertical vents are located. the vertical vents allow air to flow down through the offset trench and through the length of the trench. Hot air can escape through these vertical trenches and fresh air can enter through these same vents. The spacing between vertical trenches is calculated by United Wire, and if requested, a separate power vent is located at the end of the trench which has a fan located in it. This fan is controlled by a thermo-coupler located in the trench. This allows the user to over power the cables if needed and the extra heat generated will cause the fan to kick in and push air through the system and exit out through all the offset vents located along the trench length.
This idea has been very well received within the industry. We have presented this to many engineers throughout Canada, and we invite you to contact us and we will arrange to do the same presentation for you if you have a need for a vented trench on any project you may be working on.
Contact me at [email protected] to arrange a meeting. – Myron Vogt