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What is a short circuit, and what are the signs?
What a short circuit is, how the breaker cuts it, what sets it apart from an overload, the signs to watch for and what to do at home.
In short
This guide covers a short circuit in a home: what it is, how the breaker cuts it, and what to do.
- A short circuit is a rapid and intense overcurrent; in a home, it’s a fault in the wiring or in an appliance.
- The breaker cuts it with its magnetic trip unit; for its current-limiting breakers, ABB states that the contacts open in half a millisecond.
- An overload, on the other hand, trips the thermal unit, with a delay.
- A burning smell, an outlet heating up, sparks: in an emergency, switch off the main breaker if you can do so safely, move away and call us.
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What a short circuit is
The manufacturer ABB describes a short circuit as a rapid and intense overcurrent: the current on the circuit jumps all at once, and the breaker’s magnetic trip unit interrupts it.
Its example: the wire between a light fixture and the breaker is cut and touches ground, creating a short circuit.
In a home, a short circuit is a fault in the wiring or in an appliance.
According to the Régie du bâtiment du Québec, the breakers and fuses in a dwelling protect the conductors against excessive heat and short circuits by opening the circuit.
Short circuit, overload, ground fault
These words don’t describe the same thing.
| Problem | What happens | What cuts the power |
|---|---|---|
| Short circuit | A fault in the wiring or in an appliance: a rapid and intense overcurrent | The breaker’s magnetic trip unit |
| Overload | The circuit draws more than it is rated for | The breaker’s thermal trip unit, with a delay |
| Ground fault | Current is leaking to ground | A GFCI, outlet or breaker |
An overload is, for example, a space heater added to what is already running on the same circuit. How much a circuit can take is in our guide How many outlets on a 15 amp circuit?.
A ground fault is an unintended path between the power source and a grounded surface; GFCI outlets and breakers cut the power on this kind of leak. See our guide GFCI: what it protects, and where you need one.
How the breaker reacts
The thermal-magnetic breaker that ABB describes has two units that act independently: a thermal unit, sensitive to temperature, and a magnetic unit, sensitive to current.
On an overload, the bimetal in the thermal unit heats up and bends; the stronger the current, the faster it trips.
For its current-limiting breakers, ABB states that on a short circuit, the magnetic unit opens the contacts in half a millisecond.
A breaker that trips again as soon as you reset it, even with everything unplugged, is one of the cases where you call an electrician right away.
A breaker that keeps tripping?
We find the cause before replacing anything. The price of the diagnostic is in the written quote, at no charge.
Send my quote requestThe signs
What the Corporation des maîtres électriciens du Québec asks you to watch for on an outlet: plastic that is blackened, melted, yellowed or warped, a bubble, a burning smell.
Breakers that trip often also deserve a check by a master electrician.
The risk, according to the Régie du bâtiment du Québec: deteriorated insulation or damaged conductors can produce electrical arcs, and so a fire risk.
What to do
In an emergency, switch off the main breaker if you can do so safely, move away and call us at 438-542-7304, 24 hours a day. Our emergency electrician page explains how we respond.
If the smell comes from an appliance, unplug it or switch off its breaker.
To find the source of a short circuit, our master electricians use measuring and detection equipment.
Finding and fixing a short circuit in the wiring is an electrician’s job in Québec, even in your own home.
Frequently asked questions
What is a short circuit?
A rapid and intense overcurrent, which the breaker’s magnetic unit cuts. In a home, it’s a fault in the wiring or in an appliance.
How is it different from an overload?
An overload is a circuit drawing more than it is rated for; the breaker’s thermal unit cuts it with a delay. A short circuit is cut by the magnetic unit.
My breaker trips as soon as I reset it: what should I do?
If it trips again, even with everything unplugged, don’t keep resetting it: call an electrician.
Can a short circuit cause a fire?
The breaker opens the circuit to protect the conductors. But according to the Régie du bâtiment du Québec, deteriorated insulation or damaged conductors can produce electrical arcs, with a fire risk.
Who finds a short circuit?
A master electrician: our electricians use measuring and detection equipment to locate its source.
A breaker that keeps tripping, an outlet that gets hot?
The price is in the written quote, at no charge. For an emergency, call 438-542-7304, 24 hours a day.
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Sources
Consulted on October 30, 2026.