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Chapter 4. Electrical Wiring > In-House Electrical Wiring Cable

4.1. In-House Electrical Wiring Cable

4.1.1. Electrical Wiring Type

The Romex brand from General Cable [1] has been used for many residential electrical wirings. Within the Romex brand, NM-B type has been used for indoor branch wiring, and UF-B type, for outdoor use such as the cable to a post light. SE-U or USE-2 can be used as feeder cable for the service entrance. Both NM-B and UF-B cables are constructed with individual THHN cables of class B solid or strands of bare annealed copper conductors with an overall PVC jacket. THHN is derived from the specification of Thermoplastic insulation (PVC), High Heat resistance, and Nylon jacket. The THHN cable has a 90°C rating and is recommended for use at dry or damp locations. NM-B stands for Non-Metallic sheathed cable with class B THHN individual conductors. Similarly UF-B stands for Underground Feeder cable with class B THHN individual conductors. SE-U stands for Service Entrance Unarmored. An SE-U cable is constructed with individual THHN or individual XHHW conductors with an overall PVC jacket. XHHW is derived from the specification of XLPE (Cross-linked polyethylene) insulation, High Heat resistance, for wet and dry locations. USE-2 stands for Underground Service Entrance. The USE-2 cable is XLPE insulated and designed for direct burial application. Table 4.1 shows AWG, conductor diameter, external dimension, and ampacities of NM-B and UF-B cables for a few popular home installation choices.

These external dimensions are for cables that have a copper ground. Two-conductor cables are for normal usage, while the three-conductor cables can be used for providing two phases of electricity for a combined 240 V to supply an oven or a dryer. A three-conductor cable is also useful for connecting three-way switches. These ampacities are defined by the National Electric Code [2]. The general guidelines are illustrated by Figure 4.1.


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