· by Michael Blair, Nashville's Electrician
A breaker that trips has done exactly what it exists to do. OSHA’s electrical definitions describe a circuit breaker as a device that opens the circuit on its own when current passes a set level, and they name overload, short circuit and ground fault as the causes of that overcurrent. Swapping in a larger breaker removes the protection without removing the problem, and leaves the wire behind it exposed to more current than it was sized for, which can overheat it. The useful question is which of four conditions it is reporting.
What is a circuit overload?
Too much current on one circuit. The worked example in Square D’s bulletin on what causes AFCI trips is a bedroom circuit that shut off about 30 seconds after a hair dryer went on, with a 1,300 watt space heater, a TV, lamps and a coffee maker in another room already running: 3,600 watts on a 20 amp circuit good for 2,400. The delay is the giveaway. Overload trips are the only slow ones, taking seconds or tens of seconds by Square D’s account, and the bigger the overload, the sooner the breaker lets go.
Square D’s fix for that bedroom was to leave the heater off while the hair dryer runs. The U.S. Fire Administration’s heating safety page adds turning space heaters off when you leave the room or go to bed, and its electrical safety page says not to overload outlets or power strips. When a circuit runs out of room every winter, we move loads around or add a circuit. In the older houses we work in, one circuit often feeds more rooms than suits how people live now, so a repeat overload can be a wiring-age problem as much as a habit, and our post on space heaters and warm outlets goes further into the heater side of it.
What is a short circuit?
Hot touching neutral or ground. Square D describes a short as appearing between line and neutral or between line and ground, and says the breaker opens almost instantaneously, typically in under a tenth of a second, so the wires between the panel and the fault are not damaged. The bulletin calls old, damaged cords a common place for shorts. A failed appliance is the other usual source: if the breaker holds once that device is unplugged, the short is probably in the device.
If a breaker trips the instant it is reset with nothing plugged in, stop resetting it. Square D reads a trip with no load connected as a fault in the circuit’s own hot conductor, to neutral or to ground, and holds that the cause of a trip has to be found before the circuit goes back into service. Finding it means testing the wiring with an ohmmeter at the panel, which is where our troubleshooting and repair calls start.
Ground fault and arc fault
A GFCI trips on a small current leaking to ground. The same OSHA definitions call it a device for protecting people, one that cuts power when current to ground passes a level lower than what would trip the circuit breaker. Square D lists kitchens, bathrooms, utility rooms and outdoors as the usual places to find them, and names gradually deteriorating insulation and moisture as the most frequent causes of ground faults. A GFCI tripping in a bathroom or outside after rain is often moisture, though worn insulation or a faulty appliance will do the same, and in each case it is working. Where code calls for one is covered in our post on GFCI and AFCI requirements.
AFCI breakers watch for the signature of arcing. Square D wrote its bulletin to the 2002 National Electrical Code, which required AFCIs in residences, and it says to suspect an arc fault only after overload, short and ground fault have been examined and dismissed, because arc, short and ground-fault trips all look instantaneous. Some appliances and electronics can cause nuisance trips. Square D notes that the normal leakage from motors and power converters usually sits well under an AFCI’s trip level, and unplugging everything and adding loads back one at a time shows whether the appliance or the wiring is at fault. A repeat trip on a bedroom circuit in an older house deserves an electrician instead of a workaround.
- Trips after seconds or minutes under load: overload
- Trips instantly whenever one appliance goes on: a short in that appliance or its cord
- GFCI trips near water or outdoors after rain: ground fault, often moisture
- AFCI trips with the other causes ruled out: possible arc fault in the wiring or a cord
When it is the breaker itself
Square D’s list of causes ends with the breaker. Once everything else has been dismissed, the bulletin says, the AFCI has either been damaged or was installed improperly, and it walks an electrician through disconnecting the circuit wires from the breaker to see whether it still trips. We work the same way, from the cords back to the panel, and on a panel in a damp garage or crawl space we also look for corrosion where the breakers seat on the bus.
We get asked about older panel brands by name. We would rather open the panel and test it than repeat what is said about a brand, and if yours is original to a house built in the sixties or seventies, it is worth having us look at it while we are there for anything else. Our panel upgrade page covers what replacing one involves, and you can ask us for a free estimate on either.
Sources
- Schneider Electric (Square D), Data Bulletin 0760DB0204, Determining the Cause of AFCI Tripping (2002) — Five trip causes including the breaker itself; overload example (3,600 W on a 20 A circuit, 30 s trip) and fix; only overloads trip slowly; short paths and sub-0.1 s trip; damaged cords; no-load trip means a wiring fault; ground-fault causes and GFI locations; motor leakage below trip level; arc fault suspected last; damaged or improperly installed AFCI
- OSHA, 29 CFR 1910.399, Definitions applicable to this subpart — Definitions of circuit breaker, overcurrent (overload, short circuit, ground fault) and ground-fault circuit interrupter
- U.S. Fire Administration, Heating — Turn space heaters off when leaving the room or going to bed
- U.S. Fire Administration, Appliance and electrical — Do not overload outlets or power strips
FAQ
What a Breaker That Keeps Tripping Is Telling You — questions
Can I just install a bigger breaker?
No. The breaker is sized to protect the wire behind it, and overcurrent means any current beyond what that wire is rated to carry. Put in a breaker larger than the wire allows and the wire can overheat inside a wall without the breaker ever tripping. If a circuit keeps tripping at its proper size, the answer is less load on it or another circuit.
Why does my GFCI trip when it rains?
Most often because water is reaching an outdoor receptacle, a fixture or a cover that does not seal, and the GFCI is picking up the leakage to ground it was built to detect. Moisture and aging insulation are the two most frequent causes of ground faults. We fix where the water gets in, usually with a weather-resistant receptacle under an in-use cover and sealed penetrations, and we keep the GFCI protection in place.
Is a warm breaker panel normal?
A panel under load can feel slightly warm, and that alone is not what worries us. Hot to the touch, a burning smell, buzzing or discolored breakers are different. We tell callers who notice any of those to shut off the main if they can reach it safely and call an electrician the same day, and we treat it as a loose or failing connection until we have found otherwise.
How fast does a circuit breaker trip?
That depends on the fault. Square D’s bulletin says overloads are the only slow trips, taking seconds or tens of seconds and coming sooner the larger the overload. A short circuit opens the breaker almost at once, typically in under a tenth of a second, and ground-fault and arc-fault trips look instantaneous as well.