Understanding Wiring: Types, House Wiring Cable, Wire Colors, and Cable Sizing

Electrical wiring is essential for safely distributing power in residential, commercial, and industrial settings. Whether you’re planning to wire a new home or troubleshoot an existing installation, knowing the types of wiring, cable choices, color codes, and appropriate cable sizes is vital.

1. What Are the Three Main Types of Wiring?

In residential and light commercial applications, wiring methods generally fall into three categories:

1. Non-Metallic Sheathed Cable (NM Cable):
   – Commonly known as “Romex” (a popular brand name in the U.S.).
   – Contains insulated conductors (usually two or three) and a bare ground wire, all enclosed in a plastic sheath.
   – Widely used in house wiring due to its ease of installation and cost‑effectiveness.

2. Armored Cable (AC or MC Cable):
   – Features a metal sheath (or interlocking metal armor) that provides mechanical protection.
   – Often used in areas where extra protection is required (e.g., garages, commercial buildings, or outdoor areas).

3. Conduit Wiring:
   – Uses individual insulated wires (often THHN or THWN) run through metal or PVC conduits.
   – Preferred in applications that require extra mechanical protection, moisture resistance, or a neat, accessible installation (such as in commercial buildings or in industrial environments).

2. Which Cable Is Used for House Wiring?

For most U.S. residential applications, NM cable (Romex) is the cable of choice. It is designed for dry, indoor use and is available in various configurations (e.g., 14/2, 12/2, 12/3) where the first number indicates the gauge of the conductors and the second indicates the number of insulated wires (excluding the grounding conductor).

In other regions (such as the UK), similar functions are served by twin and earth (T&E) cables or armoured cables for extra protection in certain areas.

3. Which Color of Wire Is L and N?

Color coding varies by region. Here are the two most common conventions:

• In the United States (per NEC):
  – Live (L): Black (and sometimes red for a second live conductor)
  – Neutral (N): White
  – Ground: Bare or green

• In the United Kingdom and many IEC countries:
  – Live (L): Brown
  – Neutral (N): Blue
  – Earth: Green/Yellow striped

Always verify the local electrical code before beginning any wiring project.

Reference: Wikipedia – Electrical wiring and manufacturer datasheets.

4. What Size Cable Do I Need for Electrical Wiring?

The appropriate cable size (or gauge) depends on the circuit’s current (ampacity) and length. Here’s a basic guideline for typical residential circuits in the U.S.:

For longer cable runs, voltage drop may require upsizing the conductor. In commercial or industrial settings, precise calculations are needed using factors such as ambient temperature, conductor insulation, and installation method.

Reference: National Electrical Code (NEC) tables and electrical engineering textbooks.

Additional Related Questions & Answers

Q1: What is the difference between NM cable and conduit wiring?
Answer: NM cable is a complete assembly with a protective sheath, making it quick and easy to install indoors. Conduit wiring uses individual wires routed through a protective tube, offering more flexibility for complex or hazardous environments.

Q2: Can I use NM cable outdoors?
Answer: NM cable is not rated for outdoor use or damp locations. For outdoor wiring, use cables rated for wet or direct burial applications (such as UF cable or cables installed in conduit).

Q3: How do I calculate voltage drop for long cable runs?
Answer: Voltage drop calculations require knowledge of the conductor size, length, load current, and material. Online calculators and NEC guidelines can help determine if upsizing the cable is necessary.

Q4: What are T&E cables?
Answer: In the UK, twin and earth (T&E) cables consist of two insulated conductors plus an earth wire, commonly used for residential wiring in walls and ceiling cavities.

Comparison Table: Overview of Residential Wiring Methods

Conclusion

Understanding the three main types of wiring—non-metallic sheathed (NM) cable, armored cable, and conduit wiring—is key to selecting the right method for your project. For house wiring, NM cable (Romex) is most common in North America, while T&E cable is popular in the UK. Standard color codes designate black (or brown) for Live and white (or blue) for Neutral, though always check local codes. Cable sizing depends on the circuit’s current requirements, with typical residential applications ranging from 14 AWG for 15-amp circuits to 10 AWG or thicker for high-power applications.

For more detailed guidelines, visit:

• Wikipedia – Electrical wiring
• Southwire Residential Wiring Guide
• NEC Resources