Everything You Want to Know About UL651 PVC Conduit (2023)

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Ledes Everything you want to know about UL651 Electrical Conduit

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Descripción general

All information is explained based on UL 651 Eighth Edition, published on Oct 25, 2011, and all interpretation rights belong to UL.

Scope of Application

Schedule 40 & 80, type EB and A extruded rigid PVC conduit and fittings. UL651 applies to related fittings, including elbows, couplings, adapters, expansion, expansion-deflection, deflection joints, and rigid pipe fittings for construction. However, the UPVC material must meet the relevant requirements of ASTM 1784.

The relevant standards of UL 651 have covered the relevant standards in NEC (National Electrical Code) and NFPA 70. Schedule 40 & 80 rigid PVC conduit and fitting can be used for interior and exterior finishing or outdoor use. They must be protected from sunlight and the effects of inclement weather and can be used directly in concrete.

Schedule 40 & 80 rigid PVC conduit and fitting can be used at 50°C (122°F) to 75°C (167°F)

Works fine and can be used for 90°C (194°F) wiring needs.

Dimensions Details

For clean recycled materials or mixed materials, manufacturers must ensure that relevant standards are met, such as UL746D and UL-related standards.


Here we want to express our views. Although for the sake of environmental protection, using recycled materials or mixed production can reduce the waste of raw materials, the disadvantage is that it leads to a decrease in performance.


Then there will be a situation where many products on the market claim to be certified by relevant UL standards. Indeed, they also have compliance certificates. But in terms of performance, there is indeed a decline, such as stretch resistance.


Schedule 40 & 80 rigid PVC conduit and fitting are resistant to common corrosive influences, including alkali, hydrofluoric, and chromic acid vapors and mist, as well as pickling and electroplating, and meet the needs of users in these industrial scenarios.


Schedule 40 & 80 rigid PVC conduit and fitting inner walls should be smooth, and there should be no risk of burrs causing damage to the wires. Also, there should be no chips, blisters, cracks, spalling, scaling, chalking, or other defects on the outer surface of the tube.


The pipe body must keep the ordinate vertical and have no threads. Use a micrometer or tapered sleeve gauge to measure, the scale needs to be accurate to 0.001 inches or 0.01mm, and the measurement accuracy deviation should not exceed ±1%. The measured dimensions need to conform to the relevant specified dimensions. The relevant data already includes the tolerance range. The dimensions to be met include outer, inner, and wall thickness. In addition, like couplings, you need to measure the length, socket depth, etc.


The size requirements for Schedule 40 & 80 rigid PVC conduit are clearly described in Table 4.1. Generally speaking, the tolerance range of OD is ±0.004 to ±0.011 inch, while ID and wall thickness are specified minimum values to ensure that the required parameters are achieved.


For Type A & EB, the basic method is similar. The difference is that in this version, the OD and wall thickness of Type EB, the official description is that “Additional requirements will be added as these sizes are determined to be acceptable.”


For the quality requirements of accessories, UL651 also has some regulations, such as a smooth inner wall without burrs, which cannot affect the movement of wires. It does not allow debris, blisters, cracks, peeling, scaling, pulverization, or other defects.


UL 651 also specifies the maximum and minimum values of length, wall thickness, Socket diameter, and other parameters for all accessories to match rigid conduit. For example, for Coupling for Type EB and A conduit, under the condition of 1/2 to 6-inch trade size, the average tolerance of Inside diameter at the inner end of the socket is ±0.008 to ±0.014 inch, while the average tolerance of Inside diameter at the entrance to the socket is ±0.015 to ±0.023 inch, and the size requirements are specified in the relevant table.


There are also some special ones, which we will briefly list here. For example, in a threaded adapter suitable for threaded PVC wire and tube, the thread must be clear and clean, and the size needs to meet the requirements of ASME B1.20.1-1983. At the same time, the threaded port should have enough field and meet the bending test.


Because there are too many accessories, we will not list them here.

Performance and Testing

There are as many as 19 performance tests in UL651, which is the ultimate test for product performance. We pick the following items for some explanation,


  1. Resistencia a la tracción
  2. Extrusión
  3. Absorción de agua
  4. Resistencia al impacto
  5. Resistencia al aplastamiento
  6. Flame
  7. Permanence of Printing

Resistencia a la tracción

Use 6 samples, 3 of which have been subjected to aging tests, and then place the 6 samples on a special tensile testing instrument for testing.

There are two standards for the test results to meet the requirements. The first is that the samples that have undergone aging tests must have Tensile strength equal to or exceed those of samples that have not participated in the aging test. That is, the impact of the aging test cannot exceed 5%; the second is that the Tensile strength must meet the minimum value is 5,000 psi (34.5 MN/m2) (3.45 kN/cm2) for Schedule 40 and 80 conduit or 4000 lbf/in2 (27.6 MN/m2 or 2.76 kN/cm2 or 2812 gf/mm2) for Type A and EB rigid PVC conduit.


Simulate extruding PVC pipes using anhydrous acetone to observe and test for incomplete fusion. In general, whether there is a large area of peeling, cracking, and other problems after soaking, test whether the product meets the standard requirements. It is a great test for PVC catheters’ raw material quality and production process.

Absorción de agua

UL651 requires that after the finished PVC conduit is soaked in distilled water for 24 hours, the water absorption rate shall not exceed 0.50% of its weight. It is very easy to understand. If we bury PVC pipes in the ground, they will inevitably be affected by the moisture in the soil. If the PVC conduit absorbs too much water and swells, it will cause the conduit junction to swell and deform, resulting in a poor seal, and the result is that the wires are not protected as they should be.

Resistencia al impacto

Test with 10 PVC hard pipe samples. After the professional impact test equipment is tested, at least 7 samples should not have cracks or fragments above 1/32 inch (0.8mm) on the surface.

This test also tests the rigid tube’s rigidity, simulating its impact resistance when an external force impacts it. If it is lower than the test standard, it must be unqualified.

Resistencia al aplastamiento

Test the sample with a diameter of 6 inches to measure the deformation of the inner diameter after pressure. The inner diameter of a qualified sample after pressure shall not be less than 70% of the standard sample. Take the Schedule 40 PVC conduit as an example, and it is necessary to apply a force of 850 lbf to the conduit on the test equipment to obtain the result.


This test is different from the impact resistance test because the PVC conduit is embedded in the ground or the wall and is under pressure for a long time. This test experiments with the compressive capacity of the PVC conduit under the action of pressure, which also affects it. Factors of longevity.


The flame retardant test is to ignite the sample with a combustible gas under the premise that it is placed vertically within three test cycles of the 60s to test its flame retardant ability. Qualified samples shall not burn for more than 5s after the fire source is cut off after a test period of the 60s, and the drippings cannot ignite the cotton at the bottom.

This test simulates whether the Schedule 40 & 80 PVC conduit can provide maximum protection when threatened by fire. If the conduit has excellent flame retardancy, it can ensure that the wires in the conduit are intact when the open flame is extinguished so as not to cause a more serious accident.

Permanence of Printing

This test requires the sample to be subjected to an aging test for 168 hours in advance, soaked in tap water for 24 hours, and then rubbed with IRM902 oil to start the test. The test will use a simple automatic device to allow the tape to contact the printed part of the catheter at a fixed cycle, with a back-and-forth motion for each cycle, for a total of 50 cycles.

After the tests above, the printed characters should be clearly visible for qualified products.

Since most manufacturers are now laser engraving, this test is not too harsh. Its purpose is mainly to retain catheter printing, which can trace the manufacturer, production date, etc.


The usual PVC rigid tube printing needs to include the following:

1) With the words’ Rigid PVC conduit’;

2) Trade size

3) The name of the manufacturer or brand owner

4) Production date

5) The information above needs to be printed at least once every 10ft.

6) As stated in the chapter above, printing is permanent


In addition, there are some detailed requirements for Schedule 40 & 80 PVC conduit. For example, the printing should be updated to Schedule 40 or Schedule 80 Rigid PVC conduit for these two conduits.


Some are suitable for 90°C (194°F) wires, then the “maximum 90°C wire” should be marked on the printing. There are also some special requirements. For example, if Schedule 40 rigid conduit is only suitable for underground use, then “Underground Use Only” should be printed.


As for the printing of accessory products, because most of them are produced by injection molding technology, it only needs to be done during the mold design, and it needs to meet the permanent requirements. The printed content is generally the manufacturer’s or brand’s name and the product model. Similar to Schedule 40 or Schedule 80 Rigid PVC conduit, if it can only be used in limited scenarios, it needs to be noted, such as buried in the ground, or it is only suitable for 90°C wires.


Well, that’s all of the posts. The relevant standards of UL651 for the 3 main aspects demand size specifications, performance, and printing. However, the new performance requirement will be updated with the continuous update of the version.


If you have any questions or are interested in our UL product series, you can enviar un formulario de contacto o contact us by email or even What’s app, and we will generally reply to you within 1 business day.

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