Frequently Asked Questions



What is the VDC made out of?
TeraSpan's Vertical Deflecting Conduit (VDC) is composed of a Rigid PVC based plymere.

How strong is the VDC? Will it take the pressures of heaving?
VDC is designed to withstand 350 kilograms of pressure per linear centimeter (2,000 lbs/inch).  VDC's revolutionary "ribbed design" provides superior protection for enclosed fiber optic cables in comparison with direct buried cable with metal sheathing, traditional conduit or other micro-trenched products.  VDC protects against frost heaving and more importantly protects the cable from damage from most hand tools and the rough work environment found in most construction sites.

How durable is VDC in hostile environments?
TeraSpan is installed in regions with extreme temperature variations.  For example, installations in Winnipeg, Canada and Riyadh Saudi Arabia are some of the most challenging in the world and continue to perform as designed with no adverse effects resulting from the extreme hot/cold temperatures.  VDC withstands temperatures of -40 C (-40F) to 70 C (160 F).

Is there an impact of freezing on the cable inside the VDC?
Even if VDC is filled with water post-installation it does not come apart when the water freezes inside. VDC will shift slightly, preventing a build-up of pressure from the expanding ice and leaving cable unaffected.

Is it possible to install more fiber cables after the VDC is installed?
Yes absolutely. The installation of additional cables after the initial installation of VDC is easily completed using a pull string or blow tube/micro-duct. Pull strings and or micro-ducts may be installed during initial installation or later using a push rod or fish tape. The cost of the micro-ducting/tubing is small so in most cases it is installed during network deployment.

What is the maximum micro-duct diameter? What is the maximum capacity of the fiber micro-cable blown in the micro-ducts?
VDC accommodates up to a 6 mm micro-duct. Typically 4 mm OD is used which allows for a micro-cable/ fiber bundle of 2 to 12 fibers to be blow into the 4 mm OD micro-duct.

How long does it take to repair damaged VDC?
Once the fault point has been located, most repairs take less than 4 hours. VDC is extracted from the micro-trench, repaired, and re-installed. Designing the network with extra slack cable also improves repair time.

What type of material is used to reinstate installation cuts?
The key is that the material is applied and packed with a heavy 100 lbs packing wheel or reinstatement cart to provide a permanent bond with pavement, which prevents water from entering the micro-trench. TeraSpan recommends the use a permanent cold patch material that bonds based on pressure.  A good example is a product called Perma Patch. (See ) Some municipalities also prefer a hot tar seal for the top 2cm layer.

Does VDC require a specific fiber cable?
VIF systems require a 6 mm OD or less (smaller the cable the larger the pulling distance) that are self protecting against water which TeraSpan provides or some clients prefer to use their own supplier.

What is the longest length of VDC?
There is no limit to the length of the VDC.  The VDC is made of 2 interlocking halves, the ends of each half can be offset each other and as result any continuous length of VDC network can be made. The spools come in minimum lengths of 100 meters which are very practical for material handling in dense urban areas.

When is VDC assembled?
VDC is “zippered” or joined together just prior to deployment and then inserted into the saw cut. For smaller lengths, a zipper tool is used and for longer distances TeraSpan’s Deployment Manager is deployed with required cables, blow tubes, VDC and fixed zipper tools. 

What is the maximum trench depth and cutting disc diameter? 
The maximum trench depth is just under 270 mm when using a 66 cm disc blade using a standard 84 HP cutting machine. The depth of the trench is related to the maximum depth of the cutting machine. Larger disks are available to produce deeper trenches; however, a deeper micro-trench will reduce productivity (increase costs) and flexibility (too deep makes it harder to modify).  As mentioned above, depth is a balance with cost, deployment speed and future network flexibility.

Can the cutting machine be used on concrete, tile, rock or asphalt?
Yes to all of the above. A different machine (for example, a Trench Master) is used for cutting through soft infrastructure like soil or gravel.

How does VDC transition up a curb?
Extend the transition gradually over 2m to bring VDC up a curb. For example: to bring VDC from a 7” deep cut up a curb the cut at the start of the back of curb which is around 11” (4” for the curb height plus 7” trench) and bring it up gradually until it reaches back to 7” from the surface of the sidewalk. The slab saw is used to cut the majority on the sidewalk, curb and road. A concrete chainsaw or cut ‘n break saw is used to finish off this depth unless a large diameter cutting blade is installed on the slab saw. If VDC does a turn in the curb, the transition is much shorter because of the lateral flex of the conduit and extra room in the corner cut. TeraSpan preformed Curb Transition Clamp may be used for VDC1 and VDC4.

How often do cutting blades need to be replaced?
Three main factors impact the replacement of cutting blades: 1) wet vs. dry cutting 2) type and amount of material being cut and 3) sub layer material. As a result blade life may range from 400 to 4,000 meters.

How many meters may be completed per day? 
Productivity rates are related to crew experience, infrastructure material type, depth, traffic (pedestrian, vehicle), and weather. Higher productivity rates also occur on long route sections and low number of infrastructure/terrain changes (impacts set up times). In general, we recommend completing installation as you go so when we measure productivity, we include the following:

Productivity rates range from 75 – 125m per day in concrete, 125 – 400m/day in asphalt and 200 – 700m/Day in soil or gravel.

For larger projects these productivity rates may be significantly increased for example by using two saw cutters, larger cutting machines or by creating teams that specialize in specific functions.

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