A circuit breaker is not there to "get in the way" of the installation when several appliances are switched on. Its task is to interrupt the circuit when the current becomes greater than the one the conductors and the installation may safely carry.
When a breaker trips often, that is the consequence of some condition in the circuit.
Replacing the breaker with a stronger one without establishing the cause can remove the symptom, but at the same time it removes the protection of the conductor against overheating.
What does a circuit breaker actually protect?
A circuit breaker primarily protects the electrical line.
A conductor can safely carry only a certain current, which depends on:
- the cross section of the conductor;
- the material;
- the type of insulation;
- the way it is laid;
- the ambient temperature;
- the number of loaded conductors;
- other conditions of the installation.
If too high a current passes through a conductor for too long, it heats up.
That is why the breaker has to cut off the supply before the temperature of the conductor and of its insulation reaches a dangerous value.
So the rated current of a breaker is not chosen arbitrarily according to "how much current we need", but according to the characteristics of the line it protects.
Two basic reasons why a breaker reacts
A circuit breaker has two basic protective functions:
- protection against overload;
- protection against a short circuit.
Although the breaker cuts off the supply in both cases, the physical conditions can be very different.
Overload
An overload arises when too many appliances are working at the same time on a sound circuit.
An example:
on one circuit the following are switched on at the same time:
- a heater;
- a water kettle;
- another powerful appliance.
Each of them individually can be perfectly sound.
However, their currents add up.
If the total current exceeds the permitted value of the circuit for a longer time, the breaker will cut off the supply.
With an overload the breaker often does not react at that very instant. How much time it will need depends on the size of the current and on the characteristic of the particular protective device.
The greater the overload, the faster the reaction.
Short circuit
A short circuit is a considerably different phenomenon.
It arises when an electrical connection of very low resistance is created between conductors of different potential.
The current can then rise abruptly to values much greater than the normal working current.
In such a situation the circuit breaker should interrupt the circuit very quickly.
A short circuit can arise, for example, from:
- damage to the insulation;
- a faulty appliance;
- incorrect connection;
- mechanical damage to a cable;
- contact between conductors in a damaged socket;
- other faults in the installation.
If the breaker trips instantly every time a particular appliance or part of the installation is switched on, that is important information for the diagnosis.
Why does a conductor heat up?
Every conductor has an electrical resistance.
When a current flows through it, heat is released in it.
The basic relation is:
P = I² × R
where:
- P, the power that is converted into heat;
- I, the current;
- R, the electrical resistance.
It is important that the current in the formula is squared.
If we pass twice the current through the same conductor, the heat losses become roughly four times greater.
So increasing the permitted current is not a harmless change.
What happens if we replace a 16 A breaker with a 25 A one?
At first glance the problem can disappear.
We switch on more appliances and the new breaker no longer trips.
But by doing that we have not increased the cross section of the conductor in the wall.
We have not changed its insulation.
We have not improved the way it is laid.
We have only allowed a greater current to flow through the same line before the protection reacts.
If the conductor is not sized for that load, it can heat up excessively.
The consequences can be:
- accelerated ageing of the insulation;
- softening and deformation of the material;
- damage to the connections;
- charring of the insulation;
- an increased risk of fire.
The breaker is then no longer properly matched to the line it is supposed to protect.
A breaker is not chosen according to the appliance we want to switch on
This is one of the most important things.
If we have an appliance that requires a greater current than the existing circuit can safely provide, the solution is not automatically a stronger breaker.
The whole circuit has to be checked:
the supply source → the protective device → the conductors → the joints → the sockets or the connection point → the load.
Only when the conductor cross section, the way it is laid, the permitted current and the other parameters are known can it be determined which protection is correct.
Sometimes a new circuit of a suitable cross section has to be run.
Why does a breaker sometimes trip only after a few minutes?
That is typical of an overload.
A circuit breaker has a thermal mechanism that reacts to heating caused by the increased current.
If the current is only slightly above the permitted value, a certain time is needed for the mechanism to heat up and interrupt the circuit.
So the situation can look like this:
we switch on the heater → everything works → after ten or twenty minutes the breaker trips.
After it cools down the breaker can be switched on again.
That does not mean that "the breaker has been damaged by the heat".
It may be reacting entirely correctly to a prolonged overload.
And why does it sometimes trip immediately?
When the current suddenly becomes very large, the faster, electromagnetic function of the circuit breaker is activated.
That typically happens with a short circuit or with very large current surges.
If the breaker trips instantly when a circuit is switched on, it should not be raised again and again in the hope that "this time it will hold".
The cause has to be established.
Is every 16 A breaker the same?
No.
Besides the rated current, circuit breakers also have different tripping characteristics.
The markings most often encountered are B, C and D.
Among other things, they determine at what multiple of the rated current the electromagnetic protection will react.
That matters with loads that briefly draw a higher current when switched on, such as:
- motors;
- compressors;
- transformers;
- certain other appliances.
But changing the characteristic of a breaker is not something to be done just because the existing one "trips often".
It has to be checked whether such a change suits the whole circuit and the conditions of protection.
Sometimes the breaker itself is faulty
A protective device is not eternal either.
It is possible for a circuit breaker to become faulty over time, to have a poor connection or to react in a way that does not match its characteristic.
But that is not established by assumption.
Before replacing it, the load has to be measured and the circuit inspected.
If the current is correct, the installation is in order and the protective device still reacts improperly, only then is there a reason to suspect it.
A breaker does not protect against every electrical fault
It is also important to understand what a circuit breaker cannot do.
It is not a universal protection against:
- electric shock;
- every poor contact;
- every local overheating;
- damage that does not cause a large enough current;
- all faults of electrical appliances.
For example, a poor contact in a socket can heat up strongly at a current that is still lower than the rated current of the breaker.
So the safety of an electrical installation cannot be reduced to the single question:
"Is the breaker tripping?"
What should be done if a breaker trips often?
First the pattern has to be established.
It is important to know:
- which breaker trips;
- which appliances were switched on at that moment;
- whether it reacts immediately or after some time;
- whether the problem occurs only with one appliance;
- whether there is a smell of burning, heating or other signs of a fault.
If the problem repeats itself without an obvious reason, the installation has to be inspected and the appropriate measurements carried out.
The solution should be to remove the cause, not to prevent the protection from reacting.
The essential point
When a circuit breaker cuts off the supply, it is telling us that a condition has arisen in the circuit because of which the protection reacted.
The cause can be:
an overload, a short circuit, a faulty appliance, a problem in the installation or, more rarely, a fault of the protective device itself.
So the question should not be:
"How much stronger a breaker should we fit so that it stops tripping?"
but:
"Why is a current passing through this circuit that makes the breaker react?"
A stronger breaker does not repair a faulty or undersized installation.
It can only allow it to overheat for longer before the protection cuts off the supply.
