Line vs. Load Wiring: What’s the Difference?

There are two main types of electrical wiring used in residential and commercial buildings – line wiring and load wiring. Understanding the difference between the two is important for anyone working with electrical systems. This article will examine what line and load wiring are, how they work, and when each type is used.

What is Line Wiring?

Line wiring refers to the wires that carry electricity from the main service panel or breaker box to individual circuits. It is the wiring that connects the main power source to the various loads in a building.

Some key characteristics of line wiring:

  • Carries electricity from the main breaker panel to individual branch circuits
  • Normally operates at high voltages – typically 120V or 240V
  • Protected by circuit breakers or fuses in the main service panel
  • Conductors are usually black or red for hot wires, white for neutral, and green for ground
  • Uses heavier gauge wire than load wiring
  • Subject to more stringent installation requirements (conduit, wire sizing)

The line wiring includes the main feeders that supply power to subpanels and branch circuit wiring feeding outlets, lights, and appliances. Without line wiring distributing power, the loads could not operate.

What is Load Wiring?

Load wiring refers to the wires that connect individual devices and loads to a branch circuit. It carries electricity from the branch circuit to the point of use.

Key attributes of load wiring:

  • Connects lights, receptacles, appliances etc. to branch circuit wires
  • Operates at standard 120V in most residential wiring
  • Protected by individual breakers or fuses in distribution panels
  • Usually 12 or 14 gauge wire for 15 and 20 amp branch circuits
  • Subject to less stringent installation requirements
  • Includes fixture wires, appliance cords, and internal wiring

While line wiring feeds the branch circuits, the load wiring completes the path by delivering power to bulbs, outlets, switches, and appliances. It enables the actual usage of the electricity.

Key Differences

While line and load wiring work together to distribute power, there are some notable differences:

Voltage – Line wiring carries higher voltages from the main panel, while load wiring operates at standard 120V in residential systems.

Wire Gauge – Heavier wire gauges are used for line wiring to handle the higher voltages and current loads. Load wiring typically uses 12 or 14 gauge wire.

Protection – Line wiring has protection at the main breaker panel, while load wiring has individual circuit protection.

Installation – More stringent installation requirements for conduit, boxes, and wire sizing apply to line wiring compared to load wiring.

Purpose – Line wiring feeds power downstream to branch circuits. Load wiring connects the loads to utilize the power.

Failure Impact – A failure in line wiring can knock out power to multiple loads. Load wiring failures only affect individual devices.

Where is Line Wiring Used?

Line wiring is used for:

  • Service entrance wires from utility lines to the main breaker panel
  • Main feeders that supply electricity to subpanels
  • Branch circuit wiring running from the main panel to distribution points
  • Feeders to large appliances like HVAC equipment or electric water heaters

Basically, any wiring that distributes power from the main source outward uses line wiring. This includes almost all wiring from the main service panel except the grounding wires. Line wiring is the backbone of the electrical system.

Where is Load Wiring Used?

Load wiring applications include:

  • Individual device cords plugging into receptacles
  • Wiring inside appliances and equipment connecting individual components
  • Low voltage wiring for doorbells, alarm systems, etc.
  • Fixture wires supplying lights, ceiling fans, and other permanently installed loads
  • Receptacle pigtails, switch loops, and other termination wiring for devices

Load wiring always runs from a supply point like a panel or junction box to an actual load. It taps into the line wiring branch circuits to enable functionality of lights and plugins.

Key Installation and Sizing Requirements

Larger line wiring is subject to strict codes dictating:

  • Conduit or armor cable installation for protection
  • Proper wire sizing based on ampacity ratings for wire type
  • Current carrying capacity matched to circuit breaker size
  • Limitations on routing through wood framing and number of bends

There are fewer restrictions on how and where load wiring is installed. However, it still must meet codes for:

  • Proper insulation and heat tolerance for the application
  • Limitations on running through holes and stud/joist cavities
  • Junction box access and size requirements
  • Use of approved products for cables, cords, and terminals

While load wiring can utilize easier installation, it still must follow standard safety best practices.

Wire Color Coding

The color coding used for line and load wires also differs:

Line Wiring

  • Black – Hot or live conductor
  • Red – Second hot for 240V circuits
  • White – Neutral
  • Green or Bare – Ground

Load Wiring

  • Black – Hot for power supply to device
  • White – Neutral return to circuit
  • Green or Bare – Safety ground
  • Other colors like red, blue, yellow for switch loops and travelers

Consistent color coding is essential for identifying wire functionality for safe circuit connections.

When to Use Each Type of Wiring

In summary:

  • Any wiring from the main panel distributing power uses line wiring
  • Wiring from junction boxes to individual devices and components uses load wiring
  • Line wiring feeds the system; load wiring taps the power at endpoints

Understanding line vs load usage ensures the right wiring and protection is installed according to code requirements and manufacturer specifications.

Key Differences at a Glance

| Line Wiring | Load Wiring |
| From main panel to circuits | From circuits to devices |
| Heavier wire gauge | Usually 12/14 gauge |
| 120/240V | Standard 120V |
| More protection required | Less stringent installation |
| Backbone of electrical system | Last leg to actual loads |

Frequently Asked Questions

What are some examples of line wiring?

Some common examples of line wiring:

  • Service entrance cables from the utility supply to the main panel
  • Thick feeder wires carrying power to subpanels
  • Branch circuit wiring from panels distributing power downstream
  • Wiring to large permanently installed loads like HVAC equipment

What are some examples of load wiring?

Typical load wiring applications:

  • Lamp, ceiling fan and light fixture wiring
  • Switch loop, receptacle pigtail, and outlet wiring
  • Low voltage wiring for doorbells, thermostats, etc
  • Internal wiring of appliances connecting components
  • Device power cords plugging into outlets

Can line and load wiring be identified by wire gauge?

Generally yes, line wiring utilizes thicker wire gauges than load wiring:

  • #6, #4, #2 are common for line wiring feeders
  • #12 or #14 gauge for standard 15/20 amp load wiring
  • However, some heavy load wiring may use larger wire

The key difference is line wiring’s purpose of distributing power versus connecting loads.

How are line and load wiring treated differently for installations?

Line wiring usually requires:

  • Installation in metal conduit or armored cable
  • Strict adherence to voltage drop and sizing calculations
  • Limitations on routing through building materials

Load wiring allows:

  • More flexible nonmetallic sheathed cabling
  • Easier routing through holes and cavities
  • Less stringent sizing requirements

But all wiring must meet electrical codes for protection, support, and termination.

Can load wiring ever supply line level power?

Generally no, load wiring lacks the heavy insulation and conductor size to safely carry high amperages at line voltages. There are a few exceptions:

  • #10 gauge wiring used on some 30 amp appliance branch circuits
  • Short conduit runs to subpanels may allow smaller lines

But most line wiring applications mandate proper feeder gauge wires.


The difference between line and load wiring is an important concept in electrical work. Line wiring carries power from the main panel while load wiring connects it to endpoints. Understanding voltage levels, sizing, protection, and installation requirements ensures the proper wiring is used as dictated by codes and equipment specifications. While the two work together to distribute power, their distinct roles and requirements need to be considered.

Line Wiring Details

Line wiring is the heavy-duty electrical wiring that feeds power from the main service panel throughout the building to the individual branch circuits. It enables the distribution of electricity to all connected loads. The details of properly installing line wiring are critical for safety and operation.

Line Wiring Types

The most common types of conductor used for line wiring are:

  • Nonmetallic sheathed cable (NM) – This flexible cable contains insulated current carrying conductors and an overall plastic sheath. Romex is a common brand name. NM cable is only permitted for certain line wiring applications depending on ampacity.
  • Conduit – Rigid metal or PVC conduit provides physical protection and containment for individual THHN/THWN-2 insulated conductors. Conduit feeders are standard for large loads.
  • Metal clad cable (MC) – Provides flexible THHN/THWN-2 conductors within a wrapped or interlocking metal armor sheath. Resists moisture and physical damage.
  • Armored cable (AC) – Interlocking metal tape armor covering conductors, usually with an overall PVC jacket. Enables resistance to damage.

Properly selecting the allowed wiring types for the specific feeders and circuits ensures electrical code compliance and safe operation.

Ampacity Ratings

  • Line wiring ampacity ratings must account for:
  • Continuous or noncontinuous current draw of connected loads
  • Ambient temperature derating factors
  • Number of current carrying conductors bundled together
  • Voltage drop based on circuit length

Oversizing line wiring allows it to operate safely, efficiently, and reduce voltage drop. Undersizing can lead to hazardous overheating.

Installation Requirements

Code requirements for installing line wiring include:

  • Limiting running through wood framing members based on ampacity
  • Maintaining proper support intervals for the conductor weight
  • Ensuring required conductor clearances to other building components
  • Limiting maximum bends and securing at proper intervals when run through conduit
  • Utilizing suitable insulation for environment (wet, dry, underground)
  • Protecting against physical damage as required by location

Properly installing quality line wiring prevents hazards and ensures electrical safety.

Termination Points

Line wiring must terminate properly at:

  • Main service panel or subpanel overcurrent devices
  • Proper wire lugs, terminals, or bus bars for conductors
  • Junction boxes via clamps or knockouts when extending circuits
  • Permanent fixtures and devices like light outlets or receptacles
  • Equipment terminals designed for line wiring gauge and ampacity

Reliable line wiring terminations prevent shorts, fires, and power interruptions.

Testing and Protection

Testing line wiring involves:

  • Checking for continuity between circuit breaker panel and termination points
  • Confirming proper operation of all overcurrent safety devices
  • Measuring voltage drops remain within acceptable range
  • Verifying insulation integrity and absence of shorts

Line wiring protection is ensured by coordinated circuit breakers or fuses deenergizing faults. Proper testing confirms performance.

Adhering to all requirements when installing line wiring results in maximum safety and optimal power distribution.

Load Wiring Details

Load wiring provides the final electrical connections from junction boxes and circuits to switches, receptacles, light fixtures, and appliances. The details of properly implementing load wiring are equally as important as line wiring for operational safety.

Load Wiring Types

Typical wires used for load wiring include:

  • Nonmetallic sheathed cable – NM, Romex, etc. Standard for residential branch circuits. Easy to install exposed or through cavities.
  • Conduit – THHN/THWN individual conductors in rigid metal or PVC conduit. Used for commercial and exposed installs.
  • Metal clad cable – MC cable provides armored cable with THHN wires inside. Used to connect switches, fixtures, and outlets.
  • Low voltage wiring – Multi-conductor thermostat wire or bell wire for connecting devices under 50V.

Selecting the right load wiring enables safe connectivity to devices according to code requirements and environmental factors.

Ampacity and Voltage Drop

Properly sizing load wires involves:

  • Choosing wire gauge adequate for ampacity of the connected load
  • Considering voltage drop based on length of wire runs to loads
  • Increasing wire gauge or 15/20 amp circuit capacity if voltage drop is excessive
  • Using #10 or #12 AWG for 20 amp small appliance circuits
  • Matching low voltage wiring to device power demand

Well-designed load wiring maintains proper and efficient voltage at equipment.

Installation Considerations

Installing load wires requires attention to:

  • Securing wires properly if running through cavities and framing holes
  • Ensuring wires are not damaged by contact with building materials
  • Limiting flexible cord connections distance from junction boxes
  • Using suitable cable for environment such as wet, dry or corrosive
  • Installing per equipment manufacturer specifications and electrical codes

Properly handling and routing load wires prevents hazards and operational issues.

Connections and Terminations

Load wires terminate securely using:

  • Proper connectors matching wire gauge and type
  • Compression sleeves, splices, wire nuts, and screw terminals
  • Tight connection to device terminals without exceeding strip length
  • Sufficient junction box volume with clamps for entering cables
  • Strain relief for flexible cord connections

Reliable load wire terminations ensure robust connections to end devices or fixtures.

Testing and Protection

Verifying load wiring through:

  • Continuity testing end-to-end prior to energizing
  • Confirming proper polarity at all receptacles and fixtures
  • Checking for secure fittings and absence of shorts
  • Operating all connected devices to validate function

Individual overcurrent protection at the distribution panel protects the load wiring. Proper testing prevents hazards.

Careful installation and termination of load wiring maintains safety while delivering power where it is needed.

Choosing Appropriate Wiring

Selecting the appropriate type of electrical wiring, line or load, is essential for safety and intended circuit performance. Consider the following factors when deciding on wiring for an electrical project:

Voltage and Ampacity Requirements

  • Line wiring must be sized for voltage and ampacity ratings of connected loads
  • Load wiring requires adequate ampacity but is generally 120V
  • Match conductor insulation type and gauge to expected voltage
  • Ensure ampacity meets code for intended use including derates

Undersized wiring can present fire and electrocution hazards. Oversizing wastes money.

Installation Location and Use Conditions

  • Indoor/outdoor location determines if weatherproof wiring is needed
  • Conduit, MC, or AC wiring for protection in exposed areas
  • NM Sheathed cable for through cavities and concealed areas
  • Flexible cord for movable appliances and devices
  • Rated for use environment – wet, dry, hazardous, etc.

Install wiring designed for the locations it will be run to ensure safety.

Circuit Type and Equipment Served

  • Line wiring for distributing power downstream
  • Load wiring for connecting receptacles, lights, switches
  • Follow manufacturer specs for wiring of HVAC, appliances etc.
  • Low voltage wiring for doorbells, thermostats, alarm systems

Using line versus load wiring where intended enables proper operation.

Cost Considerations

  • Load wiring usually less expensive than heavy line wiring
  • Labor for conduit installs greater than NM cable
  • Evaluate cost vs longevity tradeoffs for different materials
  • Consider maintenance costs if wiring needs periodic replacement

Wiring that provides value over its expected usable lifetime can justify higher initial purchase and install cost.

Choosing the right wiring requires evaluating technical specifications, electrical codes, installation method, and costs. This ensures wiring safely performs as rated for its intended purpose. Consider both line and load wiring function when planning electrical projects.

Common Line and Load Wiring Mistakes

Improper installation of line or load wiring can lead to serious safety hazards and performance problems. Here are some common mistakes made and how to avoid them:

Inadequate Wire Sizing

Using under-rated wire gauges and ampacity for the application can cause:

  • Excessive voltage drop to equipment
  • Overheating from high current through small wires
  • Fires due to insulation failure
  • Nuisance tripping of breakers

Always size wires based on expected current draw with derating factors applied. Never undersize just to save on cost.

Unprotected Wiring

Failing to properly protect wiring from physical damage or moisture can lead to:

  • Loose hanging wires presenting a shock hazard
  • Rodent chewed wires causing dangerous shorts
  • Open splices leading to arcing when wires touch
  • Corroded terminals resulting in bad connections

Follow code requirements for cable protection, box volumes, strain relief, and suitable insulation.

Improper Connections

Faulty terminations such as loose screws/lugs, inadequate splices, mismatched connectors, can cause:

  • High resistance leading to voltage drop
  • Overheating and melting wire insulation
  • Intermittent functionality of lights and appliances
  • Sparks, arcing faults, and potential fires

Double check all connections are tight, matched to wire gauge, and properly secured.

Incorrect Polarity

Accidentally reversing polarity when wiring devices results in:

  • Switched hot and neutral causing shocked users
  • Motors and equipment running incorrectly or damage
  • GFCI and AFCI breakers tripping due to mismatch

Always follow manufacturer diagrams for load wiring and use a multimeter to verify.

Overloaded Circuits

Connecting too many devices and fixtures to an undersized circuit can lead to:

  • Nuisance tripping from exceeding circuit breaker amp