A 100-amp outdoor panel wired as a subpanel needs a dedicated 100-amp feeder breaker, correctly sized conductors, and neutral and ground kept separate.
A 100-amp outdoor panel is normally fed as a subpanel: power leaves a 100-amp double-pole breaker in the main panel, travels through conductors sized to the run, and lands in an enclosure built to shrug off decades of weather. Get the wire size, the neutral-ground bond, or the seals wrong and the result is a failed inspection or a real fire hazard. The practical question of how to wire a 100 amp outdoor panel comes down to five decisions: the feeder breaker, the conductor size, the wiring method, the bonding rule, and the weather seal.
Core Wiring Rules For A 100-Amp Outdoor Panel
An outdoor 100-amp enclosure is wired as a feeder-fed load center: it draws from a dedicated 100-amp double-pole breaker in whatever panel supplies it, and every connection follows the wiring diagram printed inside the enclosure plus the local electrical code. Start with a panel listed for outdoor use, with a gasket-sealed cover and enough spaces for the circuits you plan to feed. If hardware is still undecided, our best 100 amp outdoor panel options list the enclosures that carry the ratings this job needs.
Two configurations change the grounding step. When the outdoor panel is a subpanel fed from the main house panel, neutral and ground stay separated: neutrals land on an isolated bar, equipment grounds land on the enclosure’s ground bar, and no bonding jumper links them. When the outdoor panel is service equipment — the first disconnect after the meter — bonding follows the main-panel rules printed on its label. Reversing these is the most common red flag an inspector catches.
What Wire Size Feeds A 100-Amp Outdoor Panel?
Most 100-amp subpanel feeders use #4 AWG copper or #2 AWG aluminum, the sizes listed in the load-center guidance Square D and Schneider Electric publish; other wiring references cite #3 AWG copper or #1 AWG aluminum instead. The enclosure’s rating label and your local inspector settle which one applies, and long runs may need larger conductors to limit voltage drop.
| Feeder Conductors | What The Sources Say | Notes |
|---|---|---|
| #4 AWG copper | Listed in Square D/Schneider load-center guidance for 100-amp feeders | Common copper choice for a 100A subpanel |
| #2 AWG aluminum | Listed in the same guidance as the aluminum equivalent | Lighter on cost; lugs must be rated for aluminum |
| #3 AWG copper | Cited by other wire-sizing references for 100 amps | Confirm against the panel label before buying |
| #1 AWG aluminum | Cited by the same references as an alternative | Usually appears when voltage drop is a factor |
| Long feeder runs | No universal long-run size published | Up-size based on actual run length and connected load |
Aluminum is perfectly workable at this size, but it needs connectors rated for aluminum and careful torque. Copper costs more and pulls easier through conduit. Either way, the panel’s label — not a chart you found online — is the final word on the conductors it accepts, and the ampacity of the wire must meet or beat the 100-amp breaker protecting it.
Step-By-Step Installation And Sealing
Square D’s QO outdoor load center instructions anchor the sequence below: rough in the wiring, mount the enclosure, land the conductors, torque everything to the label values, then seal and lock the box so moisture never finds a way in. Most jurisdictions also require an electrical permit and an inspection before a subpanel is energized, so pull the permit before any wire is pulled.
- Plan the wiring method and route per local code, using approved conduit, cable clamps, and fittings rated for the enclosure.
- Mount the panel with its sealing gasket and hardware in place, and remove only the knockouts you actually need.
- Pull the feeder conductors into the box, secure them with approved clamps or bushings, and leave enough length to reach the terminals without strain.
- Land the two hot legs and the neutral exactly as the wiring diagram inside the enclosure shows, then connect the equipment grounding conductor to the ground bar.
- Torque every terminal to the value printed on the wiring diagram or rating label, and verify the neutral and ground bars are isolated in a subpanel installation.
- Install knockout plugs in every unused opening, seat the cover against its gasket, caulk around the box top and sides, and lock the latch.
Schneider Electric’s own QO and Homeline load center installation documentation is blunt on this point: wire each unit to its diagram and rating label, never to a generic rule. When the work is done, the cover seats flat against the gasket, every unused knockout is plugged, and each terminal holds firm at its labeled torque — that is what a passing inspection looks like before the inspector even arrives.
FAQs
Do I Need A Permit To Install A 100-Amp Outdoor Panel?
Most jurisdictions require an electrical permit and an inspection before a new subpanel is energized, and feeder work of this size rarely qualifies as a homeowner exemption. Check with your local building department before starting; failing to pull a permit can mean redoing the work, a fine, or trouble when the property is sold.
Can Neutral And Ground Share A Bar In An Outdoor Subpanel?
No. In a subpanel, keep the neutral and ground bars fully separated — no bonding screw, jumper, or shared terminal connects them. Neutrals belong on the isolated neutral bar, equipment grounds on the grounding bar bonded to the enclosure. The only exception is service equipment, where the panel is the first disconnect and bonding is required by code.
Is Aluminum Wire Okay For A 100-Amp Feeder?
Yes, when it is installed correctly. #2 AWG aluminum appears in manufacturer guidance as a listed 100-amp feeder size, and it is a common, lower-cost choice for long outdoor runs. Use connectors and lugs rated for aluminum, apply any anti-oxidant compound the manufacturer requires, and torque each termination to the label value.
References & Sources
- Schneider Electric. QO and Homeline load center installation documentation. Source for wiring-diagram, torque, and rating-label guidance.
- Square D (Schneider Electric). QO Outdoor Load Centers instruction manual. Covers gasket mounting, knockout selection, and enclosure sealing steps.
- Electrical Technology. Wire size for 100 amp service. Reference for alternative copper and aluminum conductor sizes and voltage-drop up-sizing.
