Quick answer
An electrical busbar is a solid metal strip inside a breaker panel that carries current from the incoming service to every breaker clipped onto it, so many circuits can share one power source.
Home panels have hot busbars for the breakers plus neutral and ground bars for the white and bare wires. The bus has its own amp rating, printed on the panel label, which caps the main breaker and any solar feed.
Quick facts
The key facts about Electrical Busbar, with sources:
- Made of
- Copper or aluminum; Square D QO uses copper bus, Homeline aluminum bus 2
- Solar "120% rule"
- 125% of inverter current + main breaker ≤ 120% of bus rating (NEC 2023 705.12(B)(2)) 4
- 200 A bus, 200 A main
- Max back-fed solar current 32 A (40 A breaker) 4
- Neutral bar recall
- 1.4 million Square D QO plug-on-neutral load centers, 2022 5
- Kinds in a home panel
- Hot (line) bus, neutral bar, ground bar
Key takeaways
- The busbar is the metal backbone of a panel; every breaker gets its power from it.
- The bus has an amp rating, and the main breaker may never be larger than that rating 3.
- Copper and aluminum buses are both listed and safe when the panel is used as designed 2.
- Solar that feeds a panel is limited by the bus rating through the 120% rule 4.
- Burn marks, pitting or a breaker that will not stay seated point to a damaged bus; call an electrician.
What a busbar is
Behind the row of breakers in your electrical panel sit two long metal strips. These are the hot busbars. The service wires feed them through the main breaker. Each branch breaker grips a tab, or stab, on one of them.
In a standard 120/240-volt home panel, the two hot buses carry the two legs of the service. The tabs alternate between them down the panel. That is why a single-pole breaker gives 120 volts and a two-pole breaker, which grabs both legs, gives 240 volts.
Panels also have a neutral bar for white wires and a ground bar for bare or green wires. Many newer panels use a plug-on neutral rail, so the breaker clips onto the neutral as well as the hot bus 5.
How a busbar carries current
A busbar is a short, thick conductor. Thick metal has low resistance, so it carries a lot of current with little heat. Current enters at the main lugs or main breaker and spreads out to each breaker that is turned on.
Heat is the limit. Every connection, at the lugs and at each breaker stab, has a little resistance. If a joint is loose or corroded, it heats up. Heat makes metal oxidize, which raises resistance more. That loop is how bus damage starts.
This is why the bus has a rating. The maker tests the panel and lists the most current its bus can carry. The main breaker protects the bus from going past that number.
- Dead front coverThe metal cover with breaker openings
- BreakersEach one snaps onto a bus stab
- Hot busbarsTwo legs, alternating tabs, fed by the main
- Neutral and ground barsTerminals for white and bare wires
- EnclosureThe metal box mounted to the wall
Types of busbars in a home
| Bus | Carries | What lands on it |
|---|---|---|
| Hot (line) bus | Current from the service to the breakers | Breakers, through stabs |
| Neutral bar | Return current from 120 V loads | White neutral wires |
| Plug-on neutral rail | Neutral path for plug-on AFCI and GFCI breakers | The breaker's neutral clip |
| Ground bar | Fault current only, not normal current | Equipment grounding conductors |
| Split bus (older panels) | Two separate sections, each with its own shutoffs | Several large breakers that act as mains |
Worked example: the bus limits rooftop solar
A solar inverter that back-feeds a breaker at the far end of the bus from the main adds current to that bus. IAEI Magazine works the 2023 NEC 705.12(B)(2) "120% rule" for two common panels 4.
| Step | 100 A bus, 100 A main | 200 A bus, 200 A main |
|---|---|---|
| 120% of the bus rating | 120 A | 240 A |
| Minus the main breaker | 120 − 100 = 20 A | 240 − 200 = 40 A |
| Largest solar breaker allowed | 20 A | 40 A |
| Divide by 1.25 for inverter current | 16 A | 32 A |
Many larger systems do not fit under that limit. Common answers include a smaller main breaker after a load calculation, a panel with a higher bus rating, or a supply-side connection. Each one needs a design and permit.
Where you find busbars
Every breaker panel has them, and so does each subpanel fed from it. So do meter-main combos, generator panels and the critical-loads panels used with batteries. The panel label lists the bus rating, often next to the wiring diagram.
Busbars also run inside switchgear in large buildings, where they can be many feet long. In a house, you never see the bus with the cover on, and you should not try to.
Why panels use busbars
- Compact. One bar feeds dozens of breakers without a nest of wires.
- Low heat. A thick strip carries heavy current with little loss.
- Fast changes. An electrician can add or move a breaker without rewiring the panel.
- Tested as a unit. The panel and its listed breakers are rated together.
- Clear limit. One printed rating tells you the most the panel can carry.
Copper bus vs aluminum bus
What drives the cost of bus problems
We do not quote prices. Bus bars are generally not sold as loose parts.
Square D, for example, says bus bars in its I-Line panelboards are not replaceable and the whole interior must be replaced 1.
So ask your electrician whether a matching interior exists for your model; if not, bus damage becomes a panel replacement decision.
The cost then depends on panel size, whether the service size changes, the age of the wiring that must be reconnected, permits and utility coordination. A new panel comes with a new manufacturer warranty. See what a panel replacement costs or try the cost estimator.
How an electrician checks a busbar
Checking a busbar means working with the cover off and the power controlled, so it is a job for a licensed electrician only. The five steps below show what to expect.
- They read the panel label for the bus rating and listed breakers.
- They check for heat marks, pitting, melted plastic and loose stabs.
- Some use a thermal camera with the panel loaded to find hot joints.
- They check the model against recall lists and known problem brands.
- If the bus is damaged, they plan an interior or panel replacement, with a permit and inspection where required.
What owners can do
- Keep the panel door closed and the area dry.
- Note any breaker that is hot to the touch through the door, or that buzzes.
- Find your panel model on the label and check it against the 2022 CPSC recall of Square D QO plug-on-neutral load centers 5.
- Use a free tool like our home electrical safety check.
- Book an inspection when you buy a home or before adding solar or an EV charger.
Bus damage is a fire risk
Safety and risk
A damaged or loose busbar connection gets hot, and the heat feeds itself. Signs include a burning smell, buzzing, scorch marks and breakers that trip or feel loose.
Do not open the panel or push breakers back in. Switch off the main if it is safe to reach, leave the area if there is smoke, and call an electrician or 911.
What damages a busbar
Loose connections are the most common cause. A breaker that does not grip its stab firmly arcs a little each time current flows. Over months, that pits and burns both the stab and the breaker.
Other causes: breakers that are not listed for the panel, moisture and rust, long overloads and old panel designs with known problems. Our guides on Zinsco panels and Federal Pacific replacement cover two well-known cases.
In 2022, CPSC announced a recall of about 1.4 million Square D QO plug-on-neutral load centers in the US because a loose neutral screw could overheat 5. Owners were told to contact Schneider Electric for a free inspection 5.
Rules and standards
Panels and their buses are built to UL standards and installed under the National Electrical Code, as adopted by each state. As of September 2026, 19 states had adopted the 2023 NEC in some form and six the 2026 edition 7.
Rating. Equipment must not be loaded past its listed rating; makers put it plainly: do not exceed the panel's maximum ampere rating 3. Solar.
The 2023 NEC 705.12(B) sets the limits for back-feeding a bus, including the 120% rule 4. Listed parts.
Breakers must be the types the panel label lists, which also controls where tandem breakers may go 6.
Busbar vs nearby parts
| Part | What it is | Rated in |
|---|---|---|
| Busbar | Metal strip that feeds the breakers | Amps (bus rating) |
| Main breaker | Switch and guard for the whole bus | Amps, never above the bus rating |
| Branch breaker | Guard for one circuit, clips to the bus | Amps |
| Service entrance conductors | Wires from the meter to the panel | Amps by size and type |
| Bonding jumper or screw | Ties neutral bar to the box at the service only | Sized to the service |
Busbar myths
- Myth An aluminum bus is unsafe.
- Reality Aluminum buses are listed and widely used, for example in Square D Homeline 2. The bigger risk is loose or unlisted breakers.
- Myth Any breaker that fits the bus is fine.
- Reality Only breakers listed on the panel label are approved, even if another brand clips on.
- Myth The bus rating equals the service size.
- Reality Often, but not always. A 225 A bus may carry a 200 A main. The smaller of the two sets the limit.
- Myth A burned stab can just be cleaned.
- Reality Pitted or burned bus metal usually means the panel needs replacing.
What changes by state
The solar back-feed limits come from NEC 705.12, so the exact wording you face depends on which edition your state or city has adopted. Some utilities also set their own interconnection rules. Check your edition and who is licensed to do panel work.
When the bus matters to you
You care about the bus rating at three points: adding solar, upsizing the main and spotting damage. For a plan, read the label and then run the load calculator.
- If Adding solar that back-feeds the panel
- Then Check the 120% rule against your bus and main
- If Want a bigger main breaker
- Then Confirm the bus rating first; it is the ceiling
- If Scorch marks, buzzing or loose breakers
- Then Call an electrician; expect interior or panel replacement
- If Panel model on a recall list
- Then Contact the maker for the recall remedy
Bus rating vs main rating
The bus rating is what the panel can carry. The main breaker rating is what it is allowed to carry today. The main can be smaller than the bus, never larger.
Questions about Electrical Busbar
What is a busbar in an electrical panel?
A busbar is a solid metal strip inside the panel that carries power from the main breaker to every branch breaker. Breakers clip onto tabs along it. A home panel has two hot buses for the two 120-volt legs, plus a neutral bar and a ground bar for the white and bare wires.
What does the busbar rating mean?
The busbar rating is the most current the panel's bus is listed to carry, printed on the panel label. The main breaker must not be larger than it.
If you want a bigger main or plan to add solar, the bus rating is the limit an electrician checks first.
A panel with a 225-amp bus and a 200-amp main, for example, can never take a main above 225 amps without replacing the panel 3.
Is a copper busbar better than aluminum?
Both are listed and safe when used as designed. Square D, for example, uses copper bus in its QO line and aluminum bus in Homeline. Copper resists oxidation better and is smaller for the same rating. Aluminum is lighter and lower cost. Loose or unlisted breakers matter more than bus metal.
Can a damaged busbar be repaired?
Not as a loose part, in most cases. Square D, for one, says its I-Line bus bars are not replaceable and the interior must be replaced 1. Ask an electrician whether a replacement interior exists for your exact model; if not, the fix is a new panel, with a permit and inspection where required.
What is the 120% rule for solar?
The 120% rule limits how much solar can back-feed a panel bus. Under the 2023 NEC 705.12(B)(2), 125% of the inverter current plus the main breaker rating must not exceed 120% of the bus rating. On a 200 A panel with a 200 A main, that allows 32 A of inverter current.
What causes busbar burning?
Most busbar burning starts with a loose connection, often a breaker that does not grip its stab firmly. The joint heats, oxidizes and arcs. Moisture, long overloads, unlisted breakers and known problem panels add to the risk.
Burning smells, buzzing or scorch marks need an electrician right away. Do not push a loose breaker back onto the bus yourself; the damage behind it is what needs checking.
What is the difference between a neutral bar and a ground bar?
A neutral bar carries normal return current from 120-volt loads on the white wires. A ground bar carries current only during a fault, on bare or green wires.
In the main service panel they are bonded together. In a subpanel they are kept separate, and Schneider Electric's instructions say to discard the bonding screw when a load center is used that way 3.
What is a plug-on neutral panel?
A plug-on neutral panel has a neutral rail beside the hot bus, so AFCI and GFCI breakers clip onto the neutral without a coiled pigtail wire. It makes for a neater panel.
Square D's QO plug-on-neutral line was recalled in 2022 over a loose neutral screw, so check your model. CPSC counted about 1.4 million recalled units in the US, and owners were told to contact Schneider Electric for a free inspection 5.
Sources
- Schneider Electric FAQ FA87360, replacement bus bars for damaged I-Line interiors, retrieved .
- Schneider Electric FAQ FA293376, selecting a QO (copper bus) or Homeline (aluminum bus) load center, retrieved .
- Schneider Electric FAQ FA118284, main breaker kit (maximum ampere rating, bonding screw), retrieved .
- IAEI Magazine, John Wiles, "Connecting Photovoltaic Power Systems to the Utility: Two Options" (Winter 2024, 2023 NEC), retrieved .
- U.S. CPSC, Recall 22-159: Square D QO Plug-on-Neutral Load Centers (16 June 2022), retrieved .
- Eaton Technical Data TD003004EN, Type CHT thermal-magnetic circuit breaker (data sheet, July 2014), retrieved .
- EC&M, "Wisconsin Adopts 2023 National Electrical Code" (9 September 2026), retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Bus material and rating rules from Schneider Electric; 120% rule and worked figures from IAEI (2023 NEC); recall facts from CPSC. No prices published (G-COST).
Suggest a correction. We fix errors and say what changed.