Electrical Panel Parts: Complete Guide for Homeowners

Most homeowners can name a circuit breaker and that is about as far as the electrical panel vocabulary goes. But when something stops working, or you are planning a kitchen remodel, or you want to install a 240V dryer, knowing the actual electrical panel parts is the difference between making sense of an electrician’s quote and just nodding along. The panel is not complicated – it has maybe a dozen distinct components, each with a clear job. Here is a homeowner-friendly walkthrough of everything inside that gray metal box on your basement wall.

Safety First

Before opening any panel, two safety notes. First, even with the main breaker off, the line side of the main breaker remains live. Never touch the lugs at the top of the panel. Second, removing the dead-front cover (the inner metal panel that exposes the breakers’ sides and wiring) is something most homeowners should leave to licensed electricians. The face cover with just the breaker switches visible is safe to open. The interior dead-front is not.

With that out of the way, here is what is inside.

The Service Panel Itself

The metal enclosure is the panel. Common brands in US homes:

• Square D (Schneider Electric): The QO and Homeline lines are the most common new-build panels.
• Eaton (formerly Cutler-Hammer): CH and BR series. Very common in homes built 1990 onward.
• Siemens: Q series, also widely used.
• GE: THQ and THQL series, found in many 1980s-2000s homes.
• Federal Pacific Electric (FPE) Stab-Lok: Found in 1950s-1980s homes. Notorious for failing to trip during faults. Should be replaced.
• Zinsco / Sylvania: Similar safety concerns to FPE. Replace if found.

Panels are rated for total amperage, typically 100, 150, 200, or 400 amps. The rating is printed on the panel label and limits how much electrical capacity the home can draw.

The Main Breaker (or Main Disconnect)

The largest breaker at the top (or bottom) of the panel is the main breaker. It shuts off all power to the house when switched off. The amp rating on the main breaker matches the panel’s service rating – a 200 amp service has a 200 amp main breaker.

On older homes, you may have a main disconnect outside near the meter instead of inside the panel. This is called a “split bus” or “service disconnect” arrangement.

Bus Bars (Hot Bus and Neutral Bus)

Bus bars are the metal strips that distribute power throughout the panel. A typical residential panel has:

• Two hot bus bars: Each carries 120V relative to neutral, and 240V relative to each other. Breakers clip onto these. Single-pole breakers clip to one bus. Double-pole breakers clip across both, giving 240V to the load.
• One neutral bus: A long aluminum or copper bar with screw terminals for white (neutral) wires. The neutral bus is bonded to the ground bus only at the main service panel, not at subpanels.
• One ground bus (sometimes integrated with neutral): A separate bar for bare or green ground wires. Required in subpanels and best practice in main panels.

Circuit Breakers

The switches that protect each circuit. Several types exist:

• Standard single-pole: 15 or 20 amp, 120V. Used for lighting circuits, receptacles, and small appliances.
• Double-pole: 20, 30, 40, 50, or 60 amp, 240V. Used for dryers, ranges, water heaters, EV chargers, and central AC.
• GFCI breaker: Has a small Test button. Protects against ground faults. Required for bathroom, kitchen counter, outdoor, and garage circuits if not provided at the outlet.
• AFCI breaker: Has a different Test button (often blue). Protects against arc faults. Required by current NEC for most living-space circuits in new construction.
• Combination AFCI/GFCI (Dual Function): Both protections in one. Used for kitchens and laundry under current code.
• Tandem (or duplex) breakers: Two single-pole breakers in one slot. Used when panel space is limited, but only if the panel is rated to accept them (look for a tandem-allowed marking on the label).

Service Entrance Conductors

The thick wires entering the top of the panel are the service entrance conductors. They come from the meter outside. On a 200 amp service, these are typically 4/0 aluminum or 2/0 copper – thick enough to handle the full current draw.

The service neutral typically attaches to a large lug on the neutral bus. The two hots attach to the main breaker lugs.

The Bonding Jumper

A piece of green or bare wire (or a metal screw) that bonds the neutral bus to the panel enclosure at the main service. This connection makes sure that during a fault, the panel itself does not become electrified.

Bonding is done only at the main service entrance, not at any downstream subpanel.

The Grounding Electrode Conductor

A heavy bare or green wire that runs from the neutral/ground bus to the home’s grounding electrode system – typically a ground rod driven into the earth outside or the water service pipe (or both). This provides a path for electrical faults to clear safely to earth.

Most homes have at least one 8-foot ground rod and may also bond to metal water pipes if present.

The Dead Front Cover

The metal interior cover that exposes only the breaker handles. Behind it sits the live bus bars and breaker connections. Replace this cover before powering the panel back on – it is a critical safety component, not optional.

Holes left by removed breakers must be filled with a knockout filler (about $1 each from any hardware store) to prevent finger or tool access to live bus bars.

Knockouts

The pre-cut circles in the side, top, and bottom of the panel are knockouts. They are removed (with a hammer and screwdriver, or knockout punch) to allow cable connectors and conduits to enter the panel. Each cable must enter through a connector or clamp – never raw through the metal edge.

Surge Protective Device (SPD)

A modern addition (and now required by code in new construction). A SPD is a small unit that mounts in two breaker slots and clamps voltage spikes from the utility line or lightning. Quality whole-house SPDs from Eaton, Square D, or Siemens cost $80-$250 and protect every device in the home.

Subpanels

Some homes have a separate subpanel – typically in a garage, addition, or detached structure. A subpanel looks the same as a main panel but has a few key differences:

• The main breaker (if present) does not have to match the upstream feeder rating
• Neutral and ground buses must be separated, not bonded together
• The feeder cable includes both neutral and ground conductors (4-wire feed)

How Many Circuits Can a Panel Hold?

Panel size is measured in “spaces” – how many full-size breakers can fit. Common sizes:

• 20-space panel (older homes)
• 30 or 40-space (most current 200A panels)
• 42-space (typical maximum without going to a larger panel)

Each space holds one single-pole breaker, or two slots hold one double-pole. Tandem breakers double the count where allowed.

Reading the Panel Schedule

Every panel has a panel directory inside the door listing which breaker controls which circuit. Update this any time you add or change a circuit. A well-labeled panel saves hours when troubleshooting.

Common Problems with Panels

• Double-tapped breakers (two wires under one breaker terminal that is rated for only one) – violates code and creates loose connections
• Aluminum branch circuit wiring at the panel – requires special connectors (Alumiconn or COPALUM) to prevent overheating
• Federal Pacific or Zinsco brand panels – widely considered unsafe due to high failure-to-trip rates
• Crowded or overfilled panels – heat builds up and shortens breaker life
• Rust or moisture inside the panel – sign of water intrusion that must be fixed

When to Call an Electrician

Any work behind the dead-front cover – replacing breakers, adding circuits, working on the bus bars – should be done by a licensed electrician. Panel upgrades from 100A to 200A run $1,800-$3,500. Adding a single new circuit runs $200-$500 depending on routing. Installing a whole-house surge protector runs $250-$500 installed.

Understanding electrical panel parts gives you the vocabulary to make informed decisions about your home’s electrical system. You can read a quote, plan a remodel, and spot warning signs – all without ever touching a live wire yourself.