How do I safely test and diagnose a suspected dead circuit breaker?

Direct answer

To safely test and diagnose a suspected dead circuit breaker, first reset it properly, then verify whether power is reaching the circuit using a non-contact voltage tester and a multimeter at downstream outlets or fixtures. If the circuit still appears dead and you’re comfortable working around live equipment, you can remove the panel cover (deadfront) with proper safety precautions and measure voltage at the breaker’s load terminal. A healthy single-pole breaker should deliver about 120 V to neutral/ground when ON; a double-pole breaker should show about 240 V between poles and 120 V from each pole to neutral. If there’s no output voltage while the handle is ON and other circuits are live, the breaker or the bus stab may be faulty and the breaker should be replaced. If you’re not comfortable opening a panel or you find signs of heat damage, call a licensed electrician.

What you’ll need

• Non-contact voltage tester (NCVT), rated CAT III 600 V
• Multimeter with AC voltage function (CAT III 600 V minimum)
• Insulated screwdriver set
• Flashlight or headlamp
• PPE: safety glasses, insulated gloves, and dry footwear
• Labels or masking tape for circuit identification
• Optional: clamp meter (for load checks)

Approximate costs: NCVT $15–$35, multimeter $25–$80, replacement standard breaker $8–$20, AFCI/GFCI breaker $35–$60.

Safety first

• Panels contain live parts even with individual breakers OFF. If you remove the panel cover, the hot bus remains energized unless you turn off the main breaker. If you’re unsure, stop and call a pro.
• Work with one hand when possible to reduce shock risk; keep the other away from the panel.
• Stand on a dry, insulated surface and keep the area well-lit. Never work if the panel is wet or corroded.

Quick checks before opening the panel

1. Verify a real load is connected. Plug a known-good lamp or tool into the affected receptacle or turn on a fixture on that circuit.
2. Look for a tripped handle. Some breakers show a middle position or a red indicator. To reset: firmly switch the handle fully OFF, then back ON. If it immediately trips, there may be a short.
3. Check all GFCI and AFCI devices and breakers. Press RESET on any GFCI receptacles that might be upstream. Dual-function/AFCI breakers have a TEST/RESET button—try resetting.
4. Test outlets on the circuit. Use an NCVT or a plug-in outlet tester at multiple locations to see if any are live. If some work and some don’t, you may have a loose connection (open neutral/hot) in a device box, not a bad breaker.

Panel testing (advanced)

Only proceed if you’re comfortable and equipped with proper PPE.

1. Prepare the workspace

   • Turn off sensitive electronics on the circuit. Clear the area and ensure good lighting.
   • If desired and safe, turn OFF the main breaker to remove power from the bus. Be aware: in some panels, line lugs are still live even with main OFF. Many voltage checks require the bus to be energized; if you’re not sure, stop here and call a pro.

2. Remove the deadfront

   • Use an insulated screwdriver. Keep screws in a pocketed tray. Do not touch internal metal parts.

3. Identify the suspect breaker

   • Confirm which conductor is landed on its load terminal. Verify the handle is ON.

4. Measure voltage with a multimeter (AC volts, 600 V range)

   • For a single-pole (typical 120 V) breaker: place one probe on the breaker’s load screw and the other on the neutral bar or equipment grounding bar.
   • For a double-pole (240 V) breaker: measure between the two load screws (expect ~240 V), and also from each load screw to neutral/ground (expect ~120 V each).

Expected readings:
Single-pole 120 V circuit: ~120 V (hot-to-neutral or hot-to-ground)
Double-pole 240 V circuit: ~240 V (hot-to-hot), ~120 V each (hot-to-neutral)
0 V with handle ON: suspect bad breaker, dead bus stab, or upstream issue
Trips instantly on reset: likely short to neutral/ground or a device fault

1. Compare with nearby breakers

   • If neighboring breakers show normal voltage but the suspect shows 0 V while ON, the breaker is likely bad.
   • If multiple breakers on the same side/row are dead, you may have a lost leg from the main or a damaged bus—call a pro.

2. Optional isolation (intermediate skill)

   • With the main OFF, you can loosen the load wire from the suspect breaker and cap it. Re-energize, turn the breaker ON, and re-test voltage at the breaker load screw.
   • If voltage now appears at the breaker, the branch circuit has a fault. If still 0 V, the breaker/bus is bad. Only do this if you’re confident and can do so safely.

Interpreting results

• Breaker won’t reset and trips immediately: likely a short circuit on the branch. Unplug all loads, turn off switches, and try again. If it holds then trips when a device is used, that device or a junction may be at fault.
• Breaker resets and stays ON, but no power at outlets: look for a tripped upstream GFCI or an open neutral/hot at the first device box. Check backstabbed connections and wirenuts.
• No voltage at breaker output with handle ON (others are fine): replace the breaker and inspect the bus stab for pitting or discoloration. Do not reuse a burned stab.
• 240 V breaker shows only 120 V hot-to-hot: lost leg or bad two-pole handle tie—call a pro.

Tips for best results

• Label circuits as you test; it saves time later.
• Use a known-good extension cord and lamp to verify power quickly at multiple points.
• Photograph the panel before moving any conductors.
• For AFCI/GFCI breakers, use the TEST button monthly. Nuisance trips can signal an arc or a failing breaker.

Common mistakes

• Not switching a tripped breaker fully OFF before ON.
• Relying only on a non-contact tester; always confirm with a multimeter.
• Replacing a breaker with a higher amp rating. Match the original rating and wire size.
• Working in a panel without PPE or with wet hands/feet.
• Ignoring MWBCs: shared neutrals require a 2-pole breaker or handle tie.

When to call a professional

• Burnt smell, scorching, or melted insulation in the panel.
• Corrosion, water intrusion, or aluminum branch wiring.
• Main breaker, meter, or service issues; multiple dead breakers on one leg.
• You’re not comfortable opening the panel or measuring live circuits.

Time estimate: 15–30 minutes for basic checks; 30–60 minutes for panel testing. An electrician’s diagnostic visit typically runs $150–$300, plus parts.