UL stands for Underwriters Laboratories Inc. (UL), a safety testing laboratory, is the most authoritative safety testing and certification organization in the United States and the largest private organization in the world. It is an independent, non-profit organization dedicated to public safety testing. It uses scientific testing methods to determine the presence and extent of hazards posed by various materials, devices, products, equipment, and structures to life and property. It also develops, develops, and publishes relevant standards and materials to help reduce and prevent loss of life and property, and conducts field research. In short, UL primarily engages in product safety certification and business safety certification. Its ultimate goal is to ensure that the market receives products with a reasonable level of safety, thereby contributing to the protection of human health and property. As an effective means of eliminating technical barriers to international trade, UL also plays a positive role in promoting the development of international trade. Founded in 1894, UL initially relied primarily on funding from fire insurance companies to maintain its operations. It was not until 1916 that UL became fully independent. After nearly a century of development, UL has become a world-renowned certification organization with a rigorous organizational management system, standards development, and product certification procedures. UL is governed by a board of directors comprised of safety experts, government officials, consumers, educators, utilities, the insurance industry, and representatives from standards agencies. Day-to-day operations are handled by the president and vice president. UL currently has five laboratories in the United States, with its headquarters located in Northbrook, north of Chicago, and additional laboratories in Taiwan and Hong Kong.
II. Understanding UL Electrical Wires
1. Type: CXTW (Christmas Lighting Decorative Cord), XTW (Integral Parallel Decorative Lighting Cord), SPT (Integral Thermoplastic Insulated Parallel Cord), SJT (Non-Oil Resistant Heavy Duty Cord)
2. Rated Temperature: 60-105°C
3. Maximum Voltage: 300V
4. Conductor AWG Specifications: 22, 20, 18 5. Conductor:
1) Material: Soft Annealed Copper
2) Wire Diameter: 22AWG (16/0.160), 20AWG (26/0.160), 18AWG (41/0.160)
3) Lay Pitch: a. The lay pitch of stranded wire is generally selected based on the conductor gauge. Sometimes, a different pitch may be selected to improve certain properties. For example, for communication cables, a small pitch is used to reduce attenuation, while a smaller pitch is used to provide better bending performance. (UL62: Tables 11.1, 11.2, and 11.3) b. Lay Length Measurement: Take the average of 10 lay lengths of the conductor and use it as the average lay length. When sampling, be aware that due to the significant internal stress and torque during stranding, removing the sheath may loosen the original twist structure. To this end, leave a section of sheathed wire unsheathed. Then, use a sharp blade to pull away the sheath along the cable length. Ideally, the conductor to be tested should be visible while still tightly bonded to the sheath. Lay the sample flat and straighten it. Measure the distance between the ten twist points on a given conductor as the lay length. Because stress during cabling can increase the original lay length after the sheath is formed, this is because the sheath is applied.
4) Stranded Outside Diameter: Conductors are stranded using a bundle twist method. The stranded outside diameter can be calculated using one of the following two methods: Method 1: D = d*1.154*d Method 2: d = diameter of a single conductor D = outer diameter of the stranded conductor after twisting N = number of conductors. Of the two methods above, Method 2 is more suitable for calculating the stranded outside diameter of conductors using a bundle twist method.
5) Cross-sectional Area: Measure the sum of the cross-sectional areas of each stranded core. The average diameter of at least seven strands should be used as the average core diameter. D (Calculated in Mils): Conductor Cross-sectional Area (CMA) = nd² (Circular Mil Area). Calculated in millimeters: Conductor = 0.7854 * nd².
6) Conductor Quantity Calculation: a. Single Conductor b. Stranded Conductor d - Single Conductor Diameter ρ - Conductor Density N - Number of Strands λ - Conductor Insertion Factor Note: Quantity calculations are for single-core conductors. For multi-core conductors, the insertion factor must be considered.
5. Insulation
1) Main Component: PVC (Polyvinyl Chloride)
2) Insulation Thickness: a. Measuring Tools: Micrometer (Insulation Thickness Gauge) ☐ Common micrometers, with flat end faces, have a minimum reading of 0.01mm. ☐ Load micrometer with an end face measuring 1.98 x 9.5mm and a 10g load (Conductor Insulation Thickness) * Measuring Average Insulation Thickness: Starting 10 inches from the end of the wire, measure the outside diameter of the wire at five points every 10 inches. * Insulation Thickness = (Wire Outside Diameter - Conductor Diameter) / 2. Averaging the insulation thickness at these five points yields the average insulation thickness. * Measuring Minimum Insulation Thickness: Measuring Tool: Pin-Gage Micrometer. Note: This method is suitable for wires 18AWG and larger. Cut a section of insulation, removing the core conductor, and place it on the pin of the micrometer. Gently lift the load and slowly rotate the insulation. The minimum reading is considered the minimum insulation thickness. For wires smaller than 18AWG, a reading microscope can be used. b. Measuring Tool: Reading Microscope (or Optical Projector): When sampling with a microscope, carefully remove the entire conductor core wire and slice it perpendicularly along the insulation. Measure the thickness at the thinnest point under the microscope, which is the minimum insulation thickness.
If the minimum thickness of a wire roll is found to be less than the specified value by more than 2 mils, the wire roll is deemed unqualified. If the measured value is less than the specified value by no more than 2 mils, two samples should be taken from the wire roll, one foot apart. If one of the results is less than the minimum value, the wire roll is deemed unqualified. If both measured values meet the standard, the wire roll is deemed qualified.
3) Average Jacket Thickness: The average jacket thickness is measured along the wire's outer diameter and the cable diameter at five points spaced 1 inch apart. Jacket Thickness = (Jacket Outer Diameter - Cable Diameter) / 2. The average jacket thickness is the average of the five measurements.
4) Flame Test: Wire Flame Rating and Test Method Comparison Table: Flame Rating Surface Printing: UL62: Jacket, excluding conductors; UL758: AWM Wire; Class II: Jacket, conductors, and ground wire all meet FT1 requirements.
UL62 Minimum Horizontal-Specimen UL62:
For single-core wires such as CXTW, please request a FT2 Flame Test on the outer sheath of the finished wire.
VW-1 Vertical-Specimen Flame Test UL1581(1060) UL1581(1060) Test Item Standard Section Test Object FT1 Vertical Flame Test UL1581(1060)
5) Withstand Voltage Test: A voltage corresponding to UL62 Table 51.1 should be applied between each conductor in the cable. During voltage application, the voltage should be slowly increased from zero to the rated value over 10 to 60 seconds and maintained for 1 minute. The judgment criterion is that the Hi-pot circuit alarm sounds during the voltage increase, decrease, and hold period. On the other hand, insulation resistance testing can also produce similar results to some extent, so performing a withstand voltage test first is a proactive and simple method for testing leakage.
6) Spark test For single-core power cords, such as CXTW wires, the withstand voltage test is the spark test. For multi-core power cords, the spark test can also be used instead of the withstand voltage test in daily production tests. Spark test points: OO Spark test machine Spark test machine
(1) Chrome-plated copper bead length and position: See Table 900.1, which specifies the spacing and arrangement of the beads in the horizontal and vertical directions. In daily production, it is necessary to regularly check whether the beads have fallen off. If any part is found to be incomplete, it should be replaced in time.
(2) The relationship between the length L of the spark machine V-shaped test slot, the test frequency, and the maximum output rate of the production wire can be seen in UL1581 Table 900.2. It can be seen that as the working frequency increases, the output rate can be greatly increased, and the production efficiency can also be greatly improved.
(3) Line grounding: Keep the conductor and the pay-off and take-up wheels well grounded to the spark machine. The pay-off end is a bare copper wire: the pay-off end is grounded, the take-up end does not need to be grounded, and the conductivity of the wire does not need to be tested. The pay-off end is an insulated wire: the wire is connected to the take-up and pay-off reels, and both the take-up and pay-off ends must be grounded. For 10AWG or thinner wires, the conductivity performance does not need to be tested. OO Test voltage: See UL1581 Table900.2
7) Insulation resistance test
(1) Ordinary wires and cables, ordinary wires and cables The DC voltage of the insulation megger is adjusted to 100-500V, and the wire with a length of 50FT-5000FT is soaked in a water tank for 2 hours. One electrode of the megger is connected to the copper plate electrode of the water tank, and the other electrode is connected to the wire to be tested. The measurement time is 60 seconds, and the qualified standard is that the insulation resistance of 1000 feet of wire is greater than 2.5M at 15.6℃. Convert the measured value of water temperature of 10℃-29.4℃ to the value of 15.6℃ and length of 1000 feet: IR=R*L*M*TCF/1000 R: high resistance meter reading L: measured wire length M: high resistance meter magnification TCF: temperature correction factor TCF comparison table can be found in UL1581 Table52.1 (2) Common outdoor type Common outdoor type "w" wire and cable, such as SPT--2W, SJTW, CXTW, etc. The short-term insulation resistance test method is the same as that of ordinary wire and cable, but the qualified judgment standard is completely different. The resistance of "W" type wire is much higher. For example, CXTW22AWG, the qualified standard is 15.6℃ 225M/1000 feet. a. Criteria: § SPT-2W, SPT-1W, XTW, and CXW.
See UL62 Table 35.1. § For sheathed cables such as SJTW, see UL62 Table 32.1. The insulation resistance listed in the table is the resistance value after short-term immersion in water at 15.6°C. In addition, the insulation resistance must be tested for long-term immersion in water at a rising temperature of 50°C.
b. Determining TCF: First, determine the impedance factor C. Then, find the corresponding M factor from UL62 Table 33.1. Apply the above formula to calculate the impedance. Note: For sheathed cables such as SVT and SJTW, the insulation resistance listed in the table is the insulation resistance between the conductors within the sheath. Therefore, when measuring, the outer sheath must be removed before immersion testing. Determining the impedance factor C: See UL62 Section 34. Principle: During the heating and cooling process of the two samples, measure the resistance values at 5 fixed temperature points, plot them on a semi-logarithmic coordinate, calculate the resistance value at 15.6℃, and then read the resistance value at 16.1℃. Divide the two to get the C value.
8) Tensile test before and after aging
(1) How to determine the tensile speed of the test machine? Tensile rate: When the tensile rate is not specifically specified in the tables of Section 50 of UL1581, the rate is usually 500+25mm/min.
(2) How to determine the tensile index of the material? UL62 now summarizes the physical properties of conventional flexible wires in Table 5.2 (insulation) and Table 7.2 (outer sheath). In the past, the physical properties of all plastic materials for wires were included in the UL1581 Table 50 series. For example, the physical property requirements for SPT-2 wire at 105°C are as follows: SPT-2 is an integral PVC cable, so UL62 Table 15.1 or UL1581 Table 50182 apply. The corresponding class for 105°C is 2.11, with a tensile index of 100% before aging and a tensile strength of 1500 ibf/m². At 136°C, after 7 days of aging, the elongation is 65% of the previous values, and the tensile strength is 85% of the pre-aging values.
For semi-rigid PVC (SR-PVC), according to UL1581 Table 47.1, the tensile index is listed in Table 50183: 100% elongation and 3000 ibf/m² before aging, and 70% and 70% after aging, respectively.
(3) Preparation of test samples Steps: Cut a section to be tested a. Measure the conductor diameter and the thickness of the insulation (or outer sheath); b. Carefully remove the wires and other fillers wrapped in the insulation layer, and check that the insulation surface is intact. For outer sheath samples, use a polishing grinder to carefully grind the inner surface of the outer sheath until the concave and convex parts of the inner surface are smooth. For outer sheaths with a circumference of 4mm or 6mm, dumbbell-shaped samples can be prepared using the dumbbell pieces of ASTM dieD and ASTM dieC. c. Mark the sample at both ends 1 inch apart to measure its tensile condition during the test. The clamping position of the upper and lower pulling jaws of the testing machine is uniformly spaced from the marked line and does not exceed 1/2 inch. (4) Calculation a. For a regular tubular specimen, the cross-sectional area A is: A=0.7854(D2-d2) D: outer diameter of the conductor, d: diameter of the conductor b. For a specimen with an irregular inner wall, the area A is: A=W163.87G
A: cross-sectional area, in square inches. Note: Dumbbell sheet outer sheath sample. Cross-sectional area A=average thickness of outer sheath*width c. Measurement of specific gravity G For a 10-inch long material, prepare the sample as shown below. The sample must be immersed in pure alcohol before measurement. This is mainly to avoid the retention of air on the inner wall of the sample. Measure W1: the weight of the sample in air; W2: the weight of the sample in water; W3: the weight of the bundled copper wire with a diameter less than 0.127mm. W1 G= W1-W2+W3 d、Tensile strength S=P/A P is the force to break the specimen e、Requirements for aging furnace According to ASTM D5423-93 (Type II) and ASTM D5374-93 standards: Use high-speed circulation, air, keep the oxygen content in the air around the specimen at a normal level, the circulating air rate should reach 100-200 air exchanges per hour, and the temperature should be maintained at +1.0℃.
9) Introduction to other tests
(1) Anti-ultraviolet light test After 720 hours of alternating arc and rain, the elongation and tensile strength of the specimen before and after the test should not be less than 80% of the measured value of the untested sample. This test is applicable to "W" outdoor grade wires and cables (including single wire,
