All About Electrical Wiring Types, Sizes & Installation

Electrical wiring is an essential component of any building. It allows electricity to be distributed safely throughout the structure to power lights, appliances, HVAC systems, and more. Understanding the different types of electrical wiring, proper wire sizing, and correct installation techniques is critical for every homeowner, electrician, and do-it-yourselfer. This comprehensive guide provides an in-depth look at all aspects of electrical wiring.

Types of Electrical Wiring

There are several different types of wiring used in residential and commercial buildings. The wiring types differ in their conductive material, insulation rating, and typical applications.


Copper wiring has been the standard for electrical wiring for decades. It is an excellent conductor of electricity and flexible to work with.


  • Highly conductive resulting in less voltage drop
  • Durable if properly installed
  • Resists corrosion
  • Familiar to most electricians


  • More expensive than other wiring types
  • Susceptible to theft due to scrap value

Copper building wire is available with various insulation and jacket types to meet different applications. Common forms include non-metallic sheathed cable (Romex), individual THHN/THWN-2 conductors, service entrance cable, and armored cable (AC).


Aluminum wiring was used for a short time in the 1960s and 70s before being phased out due to functional issues. Improved aluminum wiring has seen a comeback in recent years as an inexpensive alternative to copper.


  • Lower material cost compared to copper
  • Lightweight for easier installation


  • Lower conductivity requiring larger wire sizes
  • Oxides over time increasing resistance
  • Expands and contracts more than copper
  • Requires special installation and termination practices

Aluminum building wire is available in Romex and individual THHN/THWN-2 conductors. It must be properly matched with connectors and terminations rated for aluminum.

Metal Clad (MC) Cable

MC cable is a prefabricated cable assembly consisting of solid or stranded copper conductors wrapped in a thin metal armor. It is commonly used for lighting and receptacle branch circuits.


  • Armored protection from physical damage
  • Preassembled for faster installation
  • Allows easy wiring of grounded receptacles


  • Less flexible than nonmetallic cables
  • Requires anti-short bushings when penetrating metal studs
  • Limited amperage capacity

Conduit Wiring

Conduit wiring runs individual wires through metal or nonmetallic tubing for maximum protection and versatility. Popular conduit types include EMT, IMC, PVC, and flexible metal conduit.


  • Robust physical protection for wires
  • Allows easy wire changes and additions
  • Used where frequent exposure to physical damage is expected


  • More labor intensive to install
  • Individual conductors must be pulled through conduits

Any wiring type can be run through conduit. THHN/THWN-2 conductors are common in conduit systems.

Electrical Wire Size

Selecting the proper wire size is critical for safety and proper circuit operation. Wires must be sized according to ampacity and voltage drop.


Ampacity defines the maximum current a wire can continuously carry without overheating. It depends on the conductor material, insulation type, and temperature rating. For building wiring, common ampacities are 15, 20, 30, 40, 50 amps and higher. Higher ampacities require thicker wire gauges.

Circuit breakers and fuses must be sized to protect wiring. If a wire is overloaded beyond its ampacity, the breaker or fuse disconnects the circuit.

Voltage Drop

Voltage drop is the reduction of voltage as power flows through a wire. Some drop is expected, but excessive drop can cause lights to dim or motors/appliances to malfunction. Voltage drop increases as current (amperage) increases. Long wiring runs also result in larger drop.

Larger wire sizes reduce resistance and minimize voltage drop. Wires must be sized so voltage drop does not exceed 3% for feeders and 5% for branch circuits. Voltage drop is calculated based on wire size, current, and length.

Wire Installation Basics

Properly installing electrical wiring is essential for safety and optimal circuit performance.

Safety Standards

All electrical work must follow national and local electrical codes, such as the National Electrical Code (NEC) in the US. Regulations cover acceptable wiring and devices, installation methods, required safety equipment, and more.


Good routing practices keep wiring neat, avoid damage, and permit easy access:

  • Run wires in stud bays or channels
  • Follow straight paths between fixtures and boxes
  • Avoid running parallel to plumbing or crossing pipes
  • Leave appropriate lengths in boxes for connections
  • Label wires at both ends for identification


Wires and cables must be securely fastened at set intervals. Romex cables should be clipped every 4.5-6 feet and within 12 inches of boxes. Conduit runs are well supported using conduit straps.


Wires under 100 volts can safely bend to a 4” radius. Maintain larger radii for over 100 volt wiring. Use elbow conduits for turns in conduit runs.

Boxes & Devices

Proper box selection and installation ensures sufficient space for wires, clamps, and devices. Knockout holes must align with conduit runs. Fire-rated products maintain room firewalls.


Making solid terminations and connections is vital. Match wire, devices, and terminals according to type and size. Ensure connections are tight and protected from contact.

Common Residential Wiring Projects

Home electrical projects require understanding home wiring basics and how circuits are laid out. Safety should be the number one priority.

Replacing Light Switches

One of the most basic electrical projects is replacing a standard light switch. Useful tips include:

  • Turn off power at the breaker before working
  • Understand basic switch wiring configurations
  • Use a voltage tester to verify power is off
  • Carefully remove switch mounting screws and disconnect wires
  • Connect new switch the same way old switch was wired
  • Mount new switch securely in box and reconnect power

Adding New Outlets

Adding new electrical outlets involves running new wiring from the electrical panel or tapping into existing circuits. Key steps include:

  • Determine route to run wire to new outlet location
  • Choose appropriate wiring type for the run
  • Review amp load on circuit to avoid overloading
  • Turn off power and test wires to confirm they are dead
  • Run cable between outlet boxes using safe practices
  • Terminate wires securely on outlet terminals
  • Energize circuit and test outlet function

Kitchen & Bathroom Circuits

Kitchens and bathrooms have specific wiring requirements under the electrical code. Tips for these critical rooms:

  • Use only GFCI protected receptacles in kitchens, bathrooms, garages, and other wet areas
  • Ensure adequate receptacle spacing based on code
  • Use water-resistant covers and boxes in damp areas
  • Isolate major appliances like refrigerators on dedicated circuits
  • Provide exhaust fans with dedicated circuits
  • Lighting and fans must have separate circuits from receptacles

Whole House Rewiring

Rewiring an entire home is a major project that requires expertise. Key steps in a rewire include:

  • Discuss needs/goals and develop a master wiring plan
  • Obtain necessary permits for the work
  • Remove old wiring or abandon it in place if allowed
  • Run new wires from main panel through the home following plan
  • Update electrical panel if needed to meet added loads
  • Install all new outlets, switches, lights, appliances circuits per code
  • Label all circuits clearly and update house documentation

Electrical Wiring Mistakes to Avoid

Prevent hazards, outages, and damage by steering clear of these common wiring errors:

  • Overloading circuits with excess current demand
  • Undersizing wires for distance, voltage drop, and ampacity needs
  • Using unapproved wiring types like lamp cord or extension cords as permanent wiring
  • Leaving excess wire length piled in boxes rather than trimmed to proper length
  • Making loose or improper wire terminations that can arc, spark, or separate
  • Not providing GFCI protection where required
  • Running NM cables improperly through joist cavities and studs
  • Using staples or nailing cables directly through the wire damaging the insulation
  • Leaving access panels off junction boxes making stored wires unsafe

Signs of Faulty Wiring

Consistently inspect electrical systems and be alert for any signs of wiring issues. Common red flags include:

  • Discolored or cracked outlets or switch plates
  • Unusually warm outlets or plugs
  • Lights dimming or flickering
  • Circuits tripping repeatedly with no overload
  • Buzzing, sizzling, or burning smells from outlets
  • Exposed or damaged wires
  • Loose connections in panels or devices

When to Call an Electrician

While basic wiring projects are manageable for many homeowners, more complex circuits and troubleshooting may require an expert. Consult licensed electricians for:

  • Major new construction or rewiring projects
  • Upgrading electrical service panels and main feeds
  • Installation of backup generators or solar systems
  • Adding high voltage appliances like EV chargers or welders
  • Swimming pool or landscape lighting wiring
  • Repairing tripped GFCI outlets or shorted circuits
  • Investigating buzzing electrical panels or flickering lights

Master electricians have extensive training and knowledge for handling intricate wiring jobs and diagnosing issues. They ensure work is done to the National Electrical Code for safety.


Understanding electrical wiring types, proper sizing, and installation best practices allows both homeowners and tradespeople to take on wiring projects safely. While basic circuits are within reach of a competent DIYer, advanced wiring and troubleshooting electrical problems call for a licensed electrician. Following the electrical code and using caution when working with home electrical systems keeps everyone protected. For any complex wiring needs, contact a qualified electrician for assistance.

Frequently Asked Questions

What are the different types of electrical wiring?

Common wiring types include copper, aluminum, MC cable, Romex, conduit, THHN wires, service entrance, and armored cable. Different materials are used based on conductance, insulation, number of wires needed, physical protection, and cost.

How do you determine the correct wire size?

Wire size depends on the circuit amperage and acceptable voltage drop. Use larger wires for higher amp circuits and longer runs to improve conductivity and minimize voltage drop. Consult wire size charts.

What wire size is needed for a 15 amp circuit?

For a 15 amp residential circuit less than 100 feet, 12 AWG copper wire is generally suitable. For 20 amp circuits, 10 AWG is normally used. Higher amperages require progressively larger wires.

Can you put different gauge wires on the same circuit?

Wires within the same circuit should be the same gauge to avoid issues. Tap conductors can step down 1 size, but runs to outlets must match. Larger wires can transition to smaller, but not vice versa.

How deep should electrical wires be buried outside?

For trenches, burial depth depends on the wiring type:

  • Nonmetallic sheathed cable (Romex) requires 18 inches of cover
  • PVC and direct burial cables need 24 inches of burial
  • Rigid metal conduit buried underground needs just 6 inches

What size wire is needed for a 200 amp main service?

For a 200 amp 120/240V residential service, common feeder wire sizes are 2/0 copper or 4/0 aluminum, along with 2 AWG copper or 1/0 aluminum grounds. The service entry conductor sizes may vary.

How much does it cost to rewire an average house?

The average cost to fully rewire a standard 2,000 square foot home generally ranges from $8,000 to $15,000. Costs depend on labor rates, existing conditions, and the scope of the wiring project. Rewiring is a major endeavor.

What are signs you need to upgrade your electrical panel?

Signs of an overloaded, outdated panel include flickering lights, frequently tripped breakers, buzzing from the panel, blackened/warm breakers, outdated fuse panels, or not enough spaces for needed circuits. Upgrading provides capacity.

Is knob and tube wiring dangerous?

Knob and tube wiring found in older homes does not meet modern safety standards. Lack of grounding, deteriorated insulation, modifications, and insufficient capacity can make it unsafe. Replacing knob and tube wiring is recommended.

What gauge wire is commonly used for lighting circuits?

Most residential lighting circuits use 12 or 14 AWG wire. Fifteen amp lighting circuits typically use 14 AWG, while 20 amp lighting circuits use 12 AWG. Check local codes for exact requirements.


I hope this detailed overview on electrical wiring types, proper wire sizing, and safe installation techniques has been helpful. Understanding your home’s wiring and making upgrades where needed can keep electrical systems performing safely and efficiently. For any complex electrical concerns, don’t hesitate to contact a professional electrician.