What you need to know about the URD Cables
General Information about URD Cables:
• URD Cable means underground residential distribution cable. They are commonly used as service drop or power distribution cable. As can be depicted from the name, URD cables are used mainly to transmit power in residential buildings. There are different kinds of URD cables such as the quadruplex aluminum mobile, duplex aluminum, quadruplex aluminum, single conductor and triplex aluminum cable type URD. A URD cable is made of annealed wires twisted in rope-lay to optimize the surface area for transmission of current.
• It has a conductor and an insulator whose materials may vary with the area of application. The conductor consists of strands of compressed aluminum 1350 series as per ASTM B-230 which defines a cable for use in secondary distribution power circuits. The insulation is made of a cross-linked polyethylene material which gives the cable high resistance to abrasion and thereby effectively protects the underlying conductor from adverse effects of weather and harsh operating environment.
• In this post, we provide answers to some of the most commonly asked questions by customers concerning the URD cables.
1. Does URD have to be in conduit?
• No. URD cable is a direct bury wire and thus does not have to be in conduit or cable trays unless when exposed to a punishing environment above the ground or when it has to be used as a submersible cable. For conduits, the ideal types of wires are THHN and THWN which are insulated and other individual wires.
2. What is the difference between UD cable and URD cable?
• UD stands for underground distribution of electric power in conduit systems. UDs are made of study features which make them more resistance to a harsh working environment than the URDs It is ideal for use in direct burial and underground ducts. UD wires can work in both dry and wet areas even when exposed to ultraviolet rays. The conductors of a UD cable are made of copper or sometimes tinned aluminum. The conductors are stranded to provide flexibility during installation and to provide a large surface area for transmission of current. The insulation material used could either be rubber, impregnated paper or a vanished cambric. A metallic sheath is placed on the conductor to protect the conductor wire from damaging chemicals, moisture or gases while in the soil. The UD cables also have to armor to protect the insulation.
• URD cables, on the other hand, are used explicitly for underground residential purposes. They also comprise of a conductor and insulation. The conductor is made of strands of aluminum compressed as per 1350-H19. The cables come with cross-linked polyethylene insulation, and the surface of the insulator is printed for easy identification. The neutral conductor is yellow striped. URD cables are often applied as direct burial or in-ducts cables. They are used to supply secondary power of up to 600 volts.
3. Does the Quadruplex Aluminium URD Direct Burial Cable Carry any RHH Ratings?
• Yes. RHH stand for rubber high heat resistant. Type RHH conductors are often used with conduit according to the specifications set out by the National Electrical Code (NEC). In the event the Quadruplex Aluminum URD Direct Burial cable is used as type RHH, then conductor temperatures should not be more than 90 0 C in dry places, and the voltage rate should not exceed 600 volts. RHH wires are cross-linked with polyethylene insulation (XLPE).
4. Difference between URD and SE cable
• SE stands for service entrance. These groups of wires are used mainly for service entrance purposes. Due to their light weight, flexibility and easy installation, SE cables are often used in residential applications. Service entrance cables are at times made of copper or aluminum conductors. SE cables are designed for above ground installations as they can be exposed to the sun and still function optimally. Their insulation makes them retardant to flame and moisture resistant. Unless a unique arrangement has been made for them in line with their physical protection, they should not be subjected to a rigorous working environment. SE cables are constructed as per the international standard UL 854 that outlines the specifications of service entrance cables.
• Underground Residential Distribution cables on the other side are for residential applications. They are ideal for underground applications as their insulation material, a cross-linked polyethylene has outstanding features that make the cable resistant to pressure laid on the surface of the wire. However, due to the RHH rating, the insulation is not flame retardant, and thus URD cables cannot be used inside a structure. The insulation surface has printings on it to identify the wire. The conductor of underground residential distribution cables is primarily made of aluminum alloy. The construction of URD cables is as per the UL international standard and ICEA.
5. What is the technical difference between URD and Mobile Home Feeder?
Mobile home feeder (MHF) cables have dual ratings. That is RHW or THW. MHF can be used inside a dwelling or mobile home. MHF are approved for use as per the recommendations of NEC in underground and raceways installations. The conductor comprises of strands of soft drawn 8000 series aluminum according to the ASTM B-800 and B-801 standards. Mobile Home Feeder cables are constructed as per the following standards;
• UL 854 for type USE-2
• Ampacities anchored on NEC, 2005n edition, section 310-15
• UL44 for types RHH and RHW-2
Straight underground residential distribution cables, on the other hand, are majorly for outdoor applications only. URD cables can be used for direct burial use and underground applications. The conductor comprises of strands of compressed 1350 series aluminum according to the UL and ICEA standards. Underground residential distribution cables are constructed as per the following standards;
• Underwriters Laboratories 854
• ICEA S-105- 692
• Ampacities anchored on NEC
6. Does Underground Residential Distribution Cables have identification between the hots on a 120- 240 volts (1) phase system?
• Yes. The URD cables have identification between the hots on a 120-240 volts single phase system. Single phase wires come with three wires placed within the cross-linked polyethylene insulation. One is a neutral wire while the other two are hot wires. All the wires supply power with each hot wire supplying up to 120 volts of electricity. The neutral wire is tapped off from the transformer. Other than water heaters, stoves, and dryers, other home appliances usually operate on a 120 voltage power supply. This voltage uses only one hot wire and the neutral cable. Identifying the wires is quite easy as in single phase the two hot wires are surrounded by an insulation color-coded black and red. The neutral wire is white while the grounding wire is green.
7. I’m on Long Island. Will an inspector flag me if l use URD cable and run it a few feet?
• So long as the URD cable is not aged, no inspector will flag you. Underground Residential Distribution cables have tough insulation fashioned for burial. They are required to be buried 24 inches below the surface of the ground. Burying the URD cable 24 inches below the soil requires some digging. This method is ideal in areas that have land that is easy to dig. You may as well rent a trench digger. When shielded by 2 inches of concrete then the URD cables should be buried just 18 inches below the soil's surface.
8. About Monmouth 4/0-4/0-4/0 Triplex Aluminum Cable
• Monmouth 4/0-4/0-40 Triplex cable conductors are constructed with soft 1350-H19 aluminum series. It has three conductors whereby two of them are electrodes and one is a neutral conductor. Aluminum conductors are stranded to reduce the cable diameter. The conductors are insulated separately from the neutral wire with a black cross-linked polyethylene. This creates a boundary between them hence limiting any contacts, which would cause electric faults. Electrode insulation is black color coded whereas the neutral wire is yellow colored.
• Monmouth Triplex cable is a choice power line cable because it is a robust cable that can withstand harsh climatic conditions; with temperatures not exceeding 90°C. You don’t need to worry about amperage because 4/0-4/0-4/0 Triplex Aluminum has a large carrying capacity of 315 Amps. The cable is also protective from electric shocks thanks to the tough XLPE insulation. It is used for secondary power distribution.
Summary
• There are several wires and cables placed underground in our homes that help us run our day-to-day chores. Underground Residential Distribution cables supplied by Nassau Electrical are safe for use in home appliances by all users. They meet the necessary international requirements and thus safe.
• Do you have more questions on the URD cables? Our team is waiting to engage you and provide you with all the answers you need. You can also have a chat with us on the live chat pop-up on our website.