Microducts are becoming increasingly popular with engineers and owners due to the thirst for 1G+ broadband speed, and with the advent of microfiber cables. They allow home-runs from node to customer, without splicing and provide empty ducts for future connections, all within the same trench footprint. The fiber doesn't need to be installed until the customer requires it. 

The system also is passive - no electronics. The electronics, pedestals, and connections are outside the office or fiber campus. This results in an easily scalable, foolproof local network. As fiber can be blown from 3500' to 5000' under normal conditions, the footprint is quite large.

Whether microtrenching, installing Fiber to the Home, 5G wireless, or high-speed business campuses, microducts from Blue Diamond can be the right solution. 


SuperGlide® is a coextruded inner layer of low friction media in all Blue Diamond microduct products. The compound of Siloxane and HDPE lowers the already low friction factor of the microduct to below 0.12. This is a significant improvement on the Telcordia Bellcore GRE 3155 Core recommended standard of 0.15. Additionally, the inside of the microducts are ribbed. This provides turbulent airflow inside the microducts, enhancing the distances microfiber can be blown by floating the fiber inside the microducts.

If an additional liquid lubricant is used, it is recommended to use cable jetting or blowing lubricants. Pulling lubricants can be affected by the air blowing resulting in a sticky coating inside the microducts. Cable jetting lubricant can be disbursed by blowing a foam plug through the microduct prior to placing the microfiber. Proofing the microduct is a good idea. 

Oversheated microduct packages, such as 7-way 16/13 and 4-way 14/12, and even larger packages with smaller microducts have been successfully installed by boring and plowing methods. 

An expected mesh gripping tool is the recommended equipment to pull the microduct oversheath. This allows the entire tensil area of the package to be mobilized. A swivel should also be used behind the grip to ensure the microduct package can turn during pullback. 

Otherwise, standard good practice, sush as shallow entry and exit angles, backreaming the borehole, using bentonite and pulling below the safe pull strength of the conduit should be employed.

Blue Diamond's standard pull strength is calculated at approximately 40% of the yield of the package. PPI (Plastic Pipe Institute) Conduit Design Software and ASTM standards indicate using a 1300 psi safe yield. Althought conservative, it allows for some unknowns in a typical mini-directional bore. More information on mini-directional boring design can be fond on the PPI website under the PCD (Power and Communications Division)". https://plasticpipe.org/power-comm/


Override applications are the addition of single microducts into a fiber cable occupied conduit. Single or multiple seperate microducts for override applications should not be pulled as they can stretch and thus change diameter. Microducts should be blown into conduit in an override application. Contact your blowing equipment manufacturer for further information. 

Unlike the power cable industry where the areas of the cable vs. the conduit are compared, fill ratios for fiber cable and microduct are computed as the ratio of outside diameter of fiber cable to the inside diameter of the conduit.

Fill ratios in conventional conduit installations are in the 50% range, that is, as an example ½” diameter fiber would optimally blow into a 1" ID conduit.

Microcables allow larger fill ratios. Althought 50% is workable, 65% is ideal. However, 75% fill ratios in perfect field conditions, sush as straight runs with few turns and good friction properties have been accomplished.

In normal conditions, air blowing microcables into quality microducts average between 3500' to 5000' with one machine. Cascading with several machines can multiply the distances considerably. Blowing fiber can achieve rates of 300' per minute. 

UL, Underwriters Laboratories, has strict guidelines, requiring us to exactly manufacture according to their specifications.  UL 651A*, Continuous Length HDPE Conduit, and UL 1990, Nonmetallic Underground Conduit with Conductors, have four categories of pipe thickness: EPEC A (SDR 17), EPEC B (SDR 13.5), Schedule 40 and Schedule 80.  SDR11 is not a wall thickness dimension ratio listed and therefore not allowed within the UL listing.

We understand, especially when used in directional drilling, a heavier pipe is required.  In 1 '' diameter through 3' diameter, a schedule 80 pipe will match up very closely to SDR 11 wall thickness and provide the extra pull strength required.  Refer to our sizing tables for further information.

*In early 2012, UL has changed the standard numbers for plastic electrical conduit.  Previously UL 651B was the standard for Continuous Length HDPE conduit.  UL 651A was the standard for PVC and HDPE stick conduit. 


  • UL 651 A is for continuous length AND stick HDPE conduit
  • UL 651 is for PVC conduit

NEMA has just revised their Polyethylene Conduit Specification NEMA TC7. NEMA TC7-2015 has SDR 11 in the specification as well as new standards for pipe stiffness and compression.

Not much in reality.  Both resins are quality resins and the properties are virtually the same.  However, UL runs fingerprint testing on the final product of which we are certified.  Therefore, we are bound to use the same resin we have submitted to UL for approval.  Essentially, we are locked in to the exact resin we have the certifications for.

SDR is the Standard Dimension Ratio.  Technically, it is the nominal outside diameter divided by the minimum wall thickness. The larger the SDR the thinner the wall thickness.

STM is the American Society for Testing and Materials.  It is an association of manufacturers, engineers, consultants and governmental officials who write standards for all sorts of building materials, from cement, to steel and plastic pipe.  Other important specification writing bodies are NEMA (National Electrical Manufacturers Association), UL (Underwriters Laboratories) and NEC/NFPA (National Electric Code/National Fire Protection Association).

NEMA TC7 is an alternative specification to UL 651A for power applications.  Conduit made to NEMA TC7 is not UL listed, but includes additional wall thicknesses which may be appropriate for HDD applications.  The conduit will have the same strength and durability as UL listed conduit.  Refer to PPI Technical Note TN 50, Guide to Specifying HDPE Conduit for details on the various conduit specifications.

Theoretically, we can put 4" schedule 40 on a reel.  However, we don't recommend it.  As the pipe is extruded, it is wound on a reel.  As it is wound, the top of the pipe is in tension, while the bottom is in compression.  This causes the pipe to oval.  It is much more apparent in the larger diameters.  ASTM F2160 acknowledges the effect and allows for it in the specification.  4" Schedule 40 is a relatively thin wall, and so it (and Schedule 40 diameters above 4") can have a tendency to buckle.  That's why BDI does not recommend 4" Schedule 40 on a reel.  We can easily provide those diameters in stick pipe.

It depends on the size and quantity of the cable.  The NEC (National Electric Code) has guidelines on the number of conductors allowed in a HDPE Conduit.  With one conductor, it can "fill" 53% of the inside diameter of the conduit.  For 2 wires 31% and over 2 wires 40% fill ratio is allowed.  Simply multiply the area of the conductors by the quantity and compare to the inside area of the pipe.  See our "Fill Ratio Chart".

However, there are manufacturing limitations to how large and how many cables we can put in CIC (Cable in Conduit). We insert a Teflon tube through the dye to protect the cable from sticking to the hot plastic. This takes up space in the conduit and may limit the amount of cable we can extrude over. Send us an email, or contact your local Blue Diamond salesperson for further information.

The same general rules apply for fiber optic cable.

This is highly dependant on the installation.  The straighter and shorter the run, the more you can fill the casing pipe.  The longer and more complex the casing installation is, the less fill is applicable.

Generally, the recommended percentage fills are:

  • 70% (max value recommended)
  • 50% (short straight runs)
  • 30% (longer and more complex runs)

Adjust values as needed per experience.

BDI, as do other manufacturers, has the ability to co-extrude pipe.  Two extruders feed one die.  One is for an outer layer, the other an inner layer.  This allows us to change the outside color of the pipe very quickly during the manufacturing process.  The interior of the pipe is black, because that is the most common resin color for HDPE conduit and pressure pipe.  Both resins are the same quality and go through the same quality control procedures.  The layer are molecularly bonded, they cannot peel.  It is not a skin, but an integral part of the pipe.  Striped pipe is similarly co-extruded.  ASTM and other specifications allow for co-extruded pipe.  Co-extruded pipe is often used in the gas distribution market.

That is not a simple question.

The standard pressure rating of pipe is dependent on the type of resin, the diameter to wall thickness ratio, the fluid being transported, and the temperature of the application.  (Additionally, in a pipe design, fittings will affect the design pressure required of the pipe.)

The formula for pressure rating is:

PR= 2HDS Ft Af/(DR-1)

In simplest terms if Ft (service temperature) is nominal at 73 degrees F, Ft=1.0.  Also, if Af, the pipe environmental application is water, sewage or other fluids not aggressive to HDPE, then Af=1.0.

Thus the equation simplifies to PR=2HDS/(DR-1)

HDS is the Hydrostatic Design Stress.  The HDS is a rating assigned by PPI (Plastics Pipe Institute) and HSB (Hydrostatic Stress Board) for specific resins.  A PE 3408 resin will have an HDS of 800. A PE 4710 resin will have an HDS of 1000.  These resins are listed on the PPI website and TR-4 (Technical Report 4).

So for common SDR pipe, the results are quite easy to compute.

SDR     PE 3408     PE 4710

13.5     125 psi       160 psi

11        160 psi       200 psi

9          200 psi       250 psi

The above chart is true for any diameter of a particular SDR pipe, since the ratio of the OD to thickness remains constant.  DR=Do/t.

However, Schedule 40 and 80 pipe do not maintain the same OD to wall thickness ratio throughout every diameter.  Therefore a calculation of the ratio is required for each diameter.  For example: 2" Schedule 40 pipe is equivalent to SDR 15.4 (OD=2.375 t=0.154, so DR=2.375/.154=15.4).  So a 2" SCH 40, PE 3408 resin pipe would have a pressure rating of 111 psi.

Note that Schedule 40 and 80 pressure pipes are no longer typically produced.  ASTM D2447, the specification for Schedule 40 and 80 pressure pipe is now a "historical standard".  Most manufacturers are limiting their production to SDR pipe.

Chapter 3 and 5 of the PPI Handbook for Polyethylene Pipe is an excellent reference and gives more details on pipe design pressure applications.

The resin used in the manufacture of standard conduit is not pressure rated.  It does not have a HDS (Hydrostatic Design Stress) rating assigned by PPI Technical Report TR-4.  Or its HDS=0.  Therefore, conduit would not be recommended for long term pressure applications.

That being said, fiber optic cable is often "blown" into conduit.  The back pressure of blowing cable does subject the conduit to air pressure.  And for a short term, conduit will certainly stand pressure.  Blowing fiber, which is a standard installation method is perfectly suitable for conduit and innerduct applications.

Note that air pressure in plastic pipe that is not buried is a safety concern.  Contact your equipment or pipe manufacturer for further information.

PE 4710, is a high performance bi-modal pressure pipe resin, with a higher density and stress crack resistance than the standard PE 3608 pressure resin.  This allows higher pressures for the same SDR numbers.  Or conversely, the same pressure rating with lighter pipe.  For example, SDR 11 PE 3608 pipe has a pressure rating of 160 psi.  PE 4710, SDR 11 has a pressure rating of 200 psi.  Please note other environmental factors, such as operating temperature may lower the service pressure rating of the pipe.  Refer to the PPI Handbook of Plastic Pipe Chapter 6 for more information.

The cell classification is a method of identifying and specifying the raw material properties of HDPE Conduit and Innerduct.  It is a series of six numbers and one letter which describe the properties of the resin per ASTM D3350.  The numbers, in order, represent the density, melt index, flexural modulus, tensile strength, slow crack growth, hydrostatic design basis, and the letter represents whether the material is black or colored.  Blue Diamond conduit and innerduct has a standard minimum cell classification of 334480C (except the slow crack growth is >96 hrs.)  See our technical data for further information.

As defined by ASTM D 5033, regrind is "product that has been reclaimed by shredding and granulating for in-house use".  Blue Diamond has pipe cut from production for our quality control testing.  Additionally, as much as we try to make perfect pipe, we have unanticipated shut downs (thunderstorms cut off the power occasionally) or manufacture the incorrect diameter, and other miscues.  BDI grinds this pipe, and uses it in new pipe production.  The reground resin is tested to make sure the properties meet ASTM specifications.  ASTM, UL, and NEMA all allow use of regrind resin in their specifications.

Actually, if you lay HDPE conduit along a trench on a warm or hot day, the pipe will eventually relax.  Initially, the pipe will have a memory from winding on the real because the molecules align themselves during the manufacturing process of reeling, or "bending" the pipe.  You can envision, one side of the pipe will be in tension, while the opposite is in compression.  The molecules align themselves, relax and "remember" their position.  Once un-reeled, they want to relax back into the original straight positions they were during the extrusion process.

Any critical project should be engineered.  Soil conditions, the length of the bore, the diameter of the bore hole and drill rod, and changes in direction all dramatically affect the tension on the conduit.  For conduit diameters less than 8", TR-46 "Guidelines for Use of Mini-Directional Drilling for Placement of High Density Polyethylene Pipe", show simple formulas for determining the pipe wall thickness. PPI TN-48 is a quick guideline for HDD wall thickness. For diameters above 8" and long bores, refer to the engineering information in ASTM F1962, or Bore Aid Software on the PPI website.

Blue Diamond is required by law to collect sales tax in those states where we maintain an office or business presence.  If your order is shipping to one of the following states, sales tax will be charged unless you provide a valid exemption certificate:

Arkansas, Colorado, Connecticut, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Texas, Virginia, West Virginia, Wisconsin, Wyoming.

For items shipped to other states, it is the customer's responsibility to determine whether they are required to remit, directly to the state, any applicable "use" tax.  You should consult your tax adviser for further information.

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