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4/0 AWG (0000) is a large, high ampacity copper wire used to safely deliver electrical power for heavy loads in residential, commercial and industrial applications. Choosing the right size copper wire is crucial for any electrical system, but especially for high current circuits above 200 amps. This article will provide an overview of selecting, installing, and using 4/0 copper wire correctly to avoid potentially dangerous overheating conditions or nuisance tripping of overcurrent devices.
Uses for 4/0 Copper Wire
Some common applications using 4/0 building wire:
- Feeder circuits from main panels to subpanels
- Supplying power to HVAC equipment such as large air handlers
- Industrial machinery and process equipment
- Arc welders and large power tools
- Supplying marinas, RV parks, campgrounds
- Farmer’s irrigation pumps and grain dryers
- Commercial kitchen equipment
- Stage lighting and sound systems
4/0 cable is capable of carrying up to 200-250 amps depending on conditions. This makes it ideal for these high current applications.
Understanding Ampacity Ratings
The ampacity of a wire refers to its current carrying capacity, typically defined under standard conditions. For copper, 4/0 AWG has an ampacity of 200-230 amps depending on number of conductors and ambient temperature. Higher temperatures reduce ampacity ratings. The National Electrical Code (NEC) provides detailed ampacity tables to determine requirements for specific applications. Ampacity ultimately depends on:
- Conductor material (copper or aluminum)
- Insulation type
- Ambient temperature
- Number of current-carrying conductors
- Wiring method (conduit vs. open air)
Choosing the Right Wire Size
4/0 may be oversized for some circuits that require less ampacity. So it’s important use proper wire sizing calculations based on the load’s amperage demand, desired voltage drop levels across the wire length, ambient temperature, and other factors. Oversized wires are more expensive and waste space in conduit. Undersized wires present serious fire and equipment hazards. Do not size wires based solely on the size of the overcurrent device (circuit breaker or fuse). A thorough review of the NEC guides proper wire sizing.
Proper Installation Techniques
Being large and stiff, 4/0 copper can be challenging to install properly. Avoid kinking or excessively bending the wire – use wide, sweeping bends where needed. Use wire lubricant when pulling through conduit. Support the wire regularly with cable ties or bridle rings to prevent strain on connections. Make sure terminals are rated for the wire size and make tight crimps or connections. Follow manufacturer specifications for lugs – do not cut strands or reduce the conductor size. Use insulated tape at connections. Follow the NEC for required ampacity derating when bundling multiple conductors in one conduit.
Terminal and Connection Considerations
The large diameter of 4/0 copper wire requires proper terminals, connectors, and lugs rated for the size. Compression style connectors generally provide the most reliable connections for large copper wire versus screw terminals. Ensure electrical boxes and equipment enclosures allow room for making solid connections without sharply bending the wire. Use torque wrenches or drivers where specified to achieve proper tightening per manufacturer recommendations. Under-torqued connections can overheat, while over-torquing can damage the conductor or lug.
Overcurrent Protection Requirements
Protection against overloads and short circuits prevents 4/0 copper wire from overheating to unsafe levels. Fuses or circuit breakers used must not exceed the ampacity rating andAny #4 copper in a branch circuit requires overcurrent protection devices rated at 200 amps or below. The wire’s insulation can be damaged long before the 4/0 conductor actually melts from overcurrent. Proper protection also facilitates selective tripping, where the overcurrent device closest to the fault will trip first. Coordinate protection with downstream devices.
As a premium solid conductor, 4/0 copper costs more than smaller copper wires or aluminum wire. Expect to spend $5-10+ per foot for common THHN 4/0 cable, depending on factors like:
- Rising copper commodity prices
- Cable jacket type – THHN, THWN, XHHW
- Single conductors vs. multi-conductor cables
- Supply chain issues and shortages
Prices for breakers, disconnects, lugs, and connectors sized for 4/0 wire are also substantially more than those for smaller wiring. Planning carefully to use efficient wire routing and lengths helps control project costs when using 4/0 conductors.
Copper vs. Aluminum Conductors
Aluminum wire is a cheaper alternative to copper, but there are some downsides:
- Higher resistance means less ampacity than copper of the same size
- More prone to oxidative corrosion compared to copper
- More difficult to properly terminate due to hardness and coefficient of expansion
- Special terminations and connections required
These factors make aluminum less ideal for feeders over 200 amps, though it can be used if properly sized and installed. Use aluminum wire where allowed by code and equipment specs, but copper is generally preferred for large conductors like 4/0 AWG.
Important Safety Guidelines
Always exercise caution and follow best practices when working with large wires like 4/0 copper:
- De-energize circuits and use proper PPE – glasses, gloves, sturdy shoes.
- Ensure ladders or lifts are properly rated and avoid working alone.
- Use extreme care stripping insulation – nicked conductors can overheat.
- Keep hands dry when pulling wires to avoid electrocution risk.
- Carefully inspect wiring insulation for any cuts, abrasions or damage before energizing.
- Double check connections to be sure they are tight and corrosion free.
- Clearly label all circuits and disconnects.
Sample Applications and Circuit Breaker Pairings
Here are some typical 4/0 copper wire uses with associated circuit breaker sizes:
- 200 amp main electrical service panel – 4/0 copper feeder, 200A main breaker
- 60kW commercial HVAC unit – 4/0 copper branch circuit, 225A breaker
- 150A subpanel feed – 4/0 copper wire, 150A feeder breaker + 150A subpanel main breaker
- Irrigation pump motor – 4/0 copper branch circuit, 175A breaker
- Arc welding outlet – 4/0 copper wire, 200A disconnect
Note conductors are sized based on ampacity ratings, while circuit breakers used follow different sizing rules per NEC guidelines. Breakers for 4/0 copper are typically rated 150A to 250A.
4/0 copper building wire provides a flexible, reliable conductor material for feeding large electrical loads 200 amps and above. But care must be taken to properly select, size, install, and protect 4/0 copper circuits based on NEC requirements. Working safely and choosing compatible overcurrent devices, terminations, and wiring methods are also critical to realize optimal performance. While using 4/0 copper wire has higher upfront costs compared to smaller gauges, it enables infrastructure for high power applications while providing margin against overheating hazards. With good planning and electrical design, 4/0 copper wire installations achieve safety, efficiency and long-term reliability.