Complete guide: essential elements for an efficient underground installation

Underground installation is ideal for covering areas that do not yet have a fiber optic installation, or where there is not enough space to install an aerial layout. In addition, it is less visually intrusive than aerial installations. It is also the ideal method if the city council does not allow installations on facades, and more cables can be installed for future services.

We already know some elements of aerial installation, now it's time for underground installation.

One of the risks is animals; rodents that can damage the links, but if we remember; we have armored cable and the advantage of placing conduit. Below, we will describe more elements that are necessary and very useful in underground installations.

Necessary elements for an underground installation.

Underground installation requires precise planning and the use of appropriate materials to ensure its efficiency and durability. From prefabricated manholes to cable protection systems, each element plays a crucial role in the safety and stability of the infrastructure.

In this section, we will explore the essential components that ensure optimal deployment of fiber optics and electrical wiring underground, minimizing risks and improving network performance.

Micro-trencher.

To carry out the underground installation, it will be necessary to dig a trench in the ground. This trench is usually opened with robust machinery that is impractical, noisy, and cumbersome to maneuver; additionally, the trench it makes is very wide, and when refilling it, the cost of material and labor time will be greater.

Currently, there is a cutting machine called a micro-trencher that can make trenches from 2.5 cm to 80 cm wide with depths from 25 cm to 80 cm depending on the project's needs.

Micro-trenching in Tuxpanguillo, Veracruz.

This machine is small compared to classic machines used for trenching, it does not generate excessive noise and performs a very clean job, so no extra costs are required to remove debris, which also translates into savings for closing it at the end of the installation. In addition, it is operated by remote control.

Figure 2. Micro-trencher detail

Ducts, couplers and caps.

Made of high-density polyethylene, which makes it lightweight, resistant to impacts and chemicals, and recyclable. There are different diameters and thicknesses according to needs.

Duct placement in Tuxpanguillo, Veracruz

In Figure 3 you can see different conduits: the tri-tube, three conduits in one product, ideal for installations where several cables will be placed at the same time or along the same route; and the figure-8 conduit, which has a high-resistance, anti-corrosion galvanized steel messenger wire.

Figure 3. Ducts and tri-tubes.

Additionally, to connect the ducts, we have couplers, and to finish the run, caps are placed at the ends; there are aluminum and plastic ones. This way, the installation is protected and its proper functioning is ensured.

The blind cap seals the pipe, is airtight, can be pressurized and used multiple times; and as can be seen, it has an inner eyelet to fix a pulling guide.

The simplex cap can also be pressurized, but it can also be disassembled and installed after the cable or interduct. The quad-furcated cap allows up to four cables, is airtight and pressurizable; it has stainless steel nuts for better fastening and protection.

Cable installation in the duct.

Some ducts come pre-lubricated for better fiber optic cable installation, but it is recommended to apply additional lubrication to prevent friction and cable fatigue during pulling or cable blowing.

For this reason, at Incom we have products from the Polywater brand that offer our customers a solution for duct lubrication.

Cable pulling

To install the cable using the cable pulling method, a woven polyester tape or raffia, known as pulling tape, is first inserted. This tape is introduced using guides and with the help of devices known as "missiles," "socks," or "pulling spiders."

Subsequently, the cable pulling must begin, and it is important to consider forming "figure eights" to avoid twisting the cable. Even so, swivels are placed on the flexible tip that leads to the pulling guide, which in turn is attached to the pulling tape by means of an eyelet tip. To facilitate this process, we can use a pulling machine.

Figure 6. Cable pulling instruments.

Cable blowing.

Cable blowing involves installing the cable in ducts using compressors or fiber optic cable blowers. For this, the duct must not have dents, as air continuity is essential for cable installation.

It is also possible to use a missile to guide the cable, a gun with air control to regulate the air flow which in turn allows the pulling tape to be introduced. The lubricant must be different from that used for pulling.

Identification.

In underground installation, it is very important to identify the ducts and signal which service provider is passing through, so as not to excavate in the wrong places.

For this, there are signaling tapes that are usually buried and contain the legend "DANGER-DO NOT EXCAVATE-BURIED INSTALLATION" or another as required by the provider or project. These tapes must be resistant to exposure to chemicals common in the subsoil.

Underground warning tape placement.

Another type of signaling includes labels that adhere to cables or ducts, as well as self-reflective labels for more striking signaling. On the surface, brass plate tacks can be placed to identify and indicate the direction of the installations, or on roads, weather-resistant fiberglass posts could be placed.

 

Prefabricated manholes.

A manhole or inspection pit is an opening that allows access to inspect or monitor an electrical, sanitary, or telecommunications cabling installation; it also allows ventilation, preventing the accumulation of toxic and potentially explosive gases.

In the case of underground telecommunications installations, splice closures, splitters, and other passive elements such as the known racks for storing excess cable are kept in the manholes.

According to the regulations of the Ministry of Communications and Transportation (SCT) in Mexico, the manholes used must be prefabricated, and unless a project indicates or requires something different, the material must be fiberglass, its frame with polymer concrete, and the ductile iron lid with a 4L non-slip surface.

They must withstand 20 tons of compression (perfect for heavy traffic) if their location is in a metropolitan area, and their longitudinal location will be every 250 meters or at each street crossing up to a maximum of 6 per kilometer, as shown in the following figure.

Figure 9. Longitudinal location of prefabricated manholes.

There are different types of manholes: manholes (so-called because a man fits inside), mega-manholes, mini-manholes, micro-manholes, and handholes; each with different sizes according to the project's needs.