Feeder circuits are the backbone of any electrical system. They carry power from the service entrance to distribution panels, from transformers to switchgear, from main panels to sub-panels. When a feeder fails, a large section of the building goes dark.
That is why contractors take feeder wiring seriously. The wire choice matters more here than in branch circuits. And increasingly, the wire of choice is XHHW-2.
This article explains why contractors prefer XHHW-2 for feeder circuit wiring, what makes it different from other wire types, and how to select the right size for your feeders.
1. What Is a Feeder Circuit?
Before looking at wire selection, it helps to understand what a feeder circuit is.
A feeder circuit carries power from the service equipment (the main panel or switchgear) to a downstream distribution point. It does not directly supply branch circuits. Instead, it supplies sub-panels, distribution panels, or large equipment.
Feeder circuits are different from branch circuits in several ways:
- Higher current. Feeders carry the sum of all downstream loads. A feeder to a distribution panel may carry hundreds of amps.
- Longer runs. Feeders often run long distances through buildings, from the service entrance to distant panels.
- Criticality. A feeder failure affects everything downstream. Reliability is paramount.
- Voltage drop. With longer runs and higher currents, voltage drop is a significant consideration.
Because of these differences, feeder wiring requires wire that can handle sustained high currents, long distances, and critical reliability requirements.
Feeder circuit wire types are selected with these factors in mind. XHHW-2 is a leading choice for these demanding applications.
2. Why XHHW-2 Wire Is Preferred for Feeder Circuits
Several characteristics make XHHW-2 particularly suited for feeder circuits.
90°C wet/dry rating. Feeders often run through a mix of environments. Underground conduits collect moisture. Rooftop conduits see temperature extremes. Mechanical rooms may be damp. XHHW-2 maintains its full 90°C ampacity in wet and dry locations. This means the wire can carry its rated current even in damp conditions-critical for feeders that may run through wet areas.
- XLPE thermoset insulation. The cross-linked polyethylene insulation is more durable than thermoplastic alternatives. It resists heat, moisture, chemicals, and abrasion. For feeders that carry continuous loads, the insulation holds up over decades of service without degrading.
- Excellent pulling characteristics. The smooth XLPE surface reduces friction during installation. Contractors pulling XHHW-2 through long conduit runs report less effort and fewer installation problems compared to other wire types. A 3/0 AWG XHHW-2 wire, for example, pulls through conduit with less friction than THHN of the same size, saving time and labor.
- UL 44 certification. XHHW-2 is certified under UL 44, the standard for thermoset-insulated wires. This certification ensures the wire meets rigorous requirements for insulation thickness, voltage withstand, and temperature performance. Contractors and inspectors trust the UL mark.
- Wide size range. XHHW-2 is available from 14 AWG to 1000 kcmil, covering everything from small feeders to massive service entrance conductors. For XHHW-2 feeder installation, this means one wire type can serve multiple feeder applications.
XHHW-2 wire for feeders has become the standard specification in many commercial and industrial projects because it delivers reliable performance where it matters most.
3. Three XHHW-2 Sizes for Feeder Applications
Different feeders require different wire sizes. Here are three common XHHW-2 specifications used in feeder circuits.
1/0 AWG XHHW-2 Wire – Medium Feeders
The 1/0 AWG size is used for feeders in smaller commercial buildings, sub-panels in retail spaces, and equipment feeders. It provides sufficient ampacity for loads up to approximately 150A, depending on conditions. The size is manageable for installation crews while delivering reliable power to downstream panels. Contractors specify 1/0 AWG XHHW-2 when the load exceeds 2 AWG capacity but does not require larger feeders.
3/0 AWG XHHW-2 Wire – Large Feeders
The 3/0 AWG size steps up to 200A feeders. This is common for main feeders in mid-sized commercial buildings, feeders to large distribution panels, and industrial equipment power supplies. The 3/0 AWG conductor carries substantial current with acceptable voltage drop over typical feeder distances. For XHHW-2 feeder installation in medium commercial projects, 3/0 AWG is often the main feeder size.
600 kcmil XHHW-2 Wire – Heavy Feeders and Service Entrances
At the upper end, 600 kcmil XHHW-2 is used for the heaviest feeders and service entrances. This size handles the loads of large commercial buildings, industrial plants, and major distribution equipment. The 600 kcmil conductor minimizes voltage drop over long distances while providing the ampacity needed for substantial loads. Feeder circuit wire types like 600 kcmil XHHW-2 are specified where reliability and performance are critical.
4. Feeder Circuit Sizing Considerations
Selecting the right feeder wire size involves more than just looking at ampacity tables. Here are key considerations for feeder circuits.
- Continuous load. Feeders must be sized for the continuous load plus a safety margin. The NEC requires feeders to be sized at 125% of the continuous load.
- Voltage drop. Feeders often run long distances. Voltage drop can be significant. The NEC suggests limiting voltage drop to 3% for feeders and branch circuits combined, or 5% for feeders alone in some applications. Long runs may require upsizing the conductor.
- Termination temperature. Most lugs and terminals are rated 60°C or 75°C, not 90°C. Even though XHHW-2 is rated 90°C, the ampacity is often limited by the termination temperature rating. This is a common oversight in feeder sizing.
- Ambient temperature. If the feeder runs through high-temperature areas (boiler rooms, rooftops, industrial heat zones), the ampacity must be derated. The 90°C rating of XHHW-2 provides more margin for derating than 75°C rated wire.
- Conduit fill. Multiple conductors in a conduit reduce ampacity. Feeder circuits often have multiple conductors in the same conduit. Derating factors apply when more than three current-carrying conductors are in a conduit.
5. Installation Considerations for Feeder Circuits
Installing feeder circuits requires attention to detail. Here are practical tips for contractors.
- Plan the pull. Feeder runs are often long with multiple bends. Plan the pull route, use proper pulling equipment, and apply lubricant to reduce friction. XHHW-2's smooth insulation helps, but planning still matters.
- Support the cable. Heavy feeders require proper support. Use cable supports at regular intervals to prevent stress on the conductors and terminations.
- Leave service loops. At both ends, leave extra cable length. This allows for future modifications or re-terminations without replacing the entire run.
- Label clearly. Feeder circuits are critical. Clear labeling at both ends makes future maintenance and troubleshooting easier.
- Document the installation. For future reference, document the wire size, length, route, and termination details. This is helpful for maintenance and future upgrades.
XHHW-2 feeder installation is straightforward when these practices are followed. The wire's characteristics make the job easier than with many alternatives.
FAQ
Q1: What is the difference between a feeder and a branch circuit?
A feeder carries power from the service equipment to a downstream distribution point (sub-panel, distribution panel). A branch circuit carries power from the final overcurrent device to the outlets or equipment.
Q2: Why is XHHW-2 better than THHN for feeder circuits?
XHHW-2 is rated 90°C wet and dry, while THHN is 90°C dry and only 75°C wet unless dual-rated. Feeders often run through damp or wet locations, making XHHW-2 the more reliable choice.
Q3: How do I size a feeder circuit?
Determine the continuous load, multiply by 1.25, check voltage drop for the run length, and verify termination temperature ratings. Use the code tables to find the wire size that meets all requirements.
Q4: Can I use aluminum XHHW-2 for feeders?
Yes. Aluminum XHHW-2 is commonly used for large feeders, especially in commercial and industrial projects. It costs less than copper but requires larger conductor sizes and proper termination practices.
Q5: Does Greater provide UL 44 certified XHHW-2 wire for feeders?
Yes. Dongguan Greater Wire & Cable Co., Ltd. offers UL 44 certified XHHW/XHHW-2 copper building wire in sizes suitable for feeder circuits. We can provide the certificate and file number upon request.
Need XHHW-2 Wire for Your Feeder Circuit Project?
Tell us about your project-feeder size, distance, and load requirements. We will recommend the right XHHW/XHHW-2 wire size and send a quick quote.
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Dongguan Greater Wire & Cable Co., Ltd.
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