How to choose a circuit breaker for power, current for home

Now the presence of circuit breakers in the electrical network of any home is already a common practice.

If earlier such a switch was available on the network, then only at the entrance of the wiring to the house.

Now they are installed on different branches of the house network, which supply electrical energy to certain consumers.

Circuit breaker functions

Usually, the knowledge of the owner of the house about these switches comes down to the fact that they protect devices connected to the network or one of its branches from overload.

And this is true, but this is only a consequence of the operation of this device.

The main purpose is to protect the wiring from exceeding current values, primarily critical ones.

In short, when the current is exceeded, the switch will de-energize that part of the wiring that is attached to its output terminals. It’s just how it works can be different.

With a slight increase in current, it will de-energize the network after a certain period of time.

But with a sharp jump, which usually occurs during a short circuit, the switch will work almost instantly, which will protect the wiring from melting and possible ignition.

If we consider the circuit breaker externally, then it is not particularly complex in design – just a plastic box with terminals for connecting wiring and a small toggle switch for turning it on and off.

But this is only outwardly.

Circuit breaker design

Its internal structure is not so simple.

The body contains:

• cocking mechanism;
• Thermal installation screw;
• Bimetallic thermal release;
• Electromagnetic coil release;
• arc chute;
• Power contacts;
• Channel for the removal of hot gases.

Each of these elements does a specific job. Read on the topic – what is a difavtomat, how to connect it.

The cocking mechanism is connected to a toggle switch, and power contacts are installed at its ends. They also transfer electric current from the incoming terminals to the outgoing ones.

The bimetallic (thermal) release is a plate that bends when heated, separating the power contacts.

This release is intended to stop the supply of current if its strength does not have a peak value.

With a slight excess of current, over time, the plate will heat up and the contacts will open. That is, this release is triggered after a certain time.

The screw adjusts the gap between the plate and the contact. This screw is adjusted at the factory.

The electromagnetic release is designed for instant de-energization of the network. It works only when exposed to high currents that occur during a short circuit.

When one of the releases is triggered, an electric arc will inevitably occur between the contacts, and the greater the current, the stronger it is.

So that this arc does not lead to damage to the elements of the switch, its design includes an arc chute, which extinguishes the arc that has arisen inside itself.

With all this, gases with an elevated temperature are formed inside, which are discharged through a special channel.

Structurally, all circuit breakers are almost the same, but their operating parameters differ.

There are certain criteria for selecting circuit breakers, which take into account their parameters.

Main characteristics of circuit breakers

Short circuit current

The first of the criteria that is taken into account when choosing a machine is the short-circuit current, which is also the breaking capacity of the circuit breaker.

This criterion characterizes the maximum value of the current strength at which the machine will work without getting damaged.

This indicator is measured in Amperes, but since during a short circuit the current strength can reach significant levels, this criterion for the machine is indicated in thousands of Amperes.

Current value

The second criterion when choosing is the nominal value of the current strength with which the circuit breaker will operate.

This criterion indicates the strength of the current, above which the machine will operate and a power outage will occur.

This indicator is influenced by many factors – the cross section of the wire, the material of its manufacture, the length of the wiring to the machine, the load that will be created in the wiring when connecting electrical appliances.

Operate current

This indicator indicates what maximum current strength the circuit breaker can withstand without tripping the electromagnetic release.

The fact is that when the devices are turned on, starting currents can occur, which are often several times higher than the nominal value, but they are not a short circuit current. For example, when you turn on your computer.

These inrush currents are short-lived and therefore do not trip the thermal breaker because they take time and are not strong enough to trip the magnetic breaker.

The criterion is divided into classes that indicate how many times the inrush current can exceed the rated current without the machine tripping.

Selectivity

Based on the first three criteria, it is conditionally possible to divide all machines for use into:

1. Lightly loaded networks;
2. Medium loaded;
3. Highly loaded networks.

At the same time, using, for example, a highly loaded machine for a network branch that provides power to light bulbs is not only impractical, but also dangerous.

Its characteristics are much higher than required for such a network, so even if a short circuit occurs, it may simply not work.

Conversely, an automaton for low-load networks, when used on networks with a large load, will work even with small overloads.

The number of poles of the machine indicates which type of networks it can work with.

A two-pole switch is suitable for a conventional single-phase home network.

To provide a separate section of this network, a single-pole machine is suitable.

But if there is a three-phase network in the house, then you need a four-pole switch.

But these are only criteria indicating the main characteristics. It should be noted that all of them are applied in the form of markings on the body of the circuit breaker.

Now, using an example, we will explain what each of the elements of this marking is responsible for.

Switch marking designation

All machines have large alphanumeric markings (B10, C16, C10, D50).

This marking includes two parameters of the circuit breaker: the operating current class and the rated voltage current.

There are three classes in total – B, C and D. Each of them has its own multiplicity of current strength in relation to the nominal value.

So, a class “B” machine is able to accept a current strength 3-5 times greater than the nominal value, before it disconnects the contacts. Such machines are suitable for lightly loaded networks.

In class “C”, the current strength before the machine trips can reach a 5-10-fold increase compared to the nominal value. An automaton with this class is already designed for medium-loaded networks.

Class D is intended for high-load networks, where a short-term significant increase in current strength is possible. Such an automaton can withstand, until triggered, a current with a force exceeding the nominal value by 10-20 times.

The second value of this marking indicates just the nominal value of the current with which the switch will operate.

The main parameter when choosing according to this value is the cross section of the wire.

The cross section of the wire determines how much current can pass through it.

So, a copper two-core wire with a cross section of 1,5 mm. sq., laid in a closed way (in a strobe or pipe) can pass a current of 18A through itself without causing damage to the wire itself.

If this value is exceeded, the wire will start to heat up, which can lead to melting of the insulation, and without it, a short circuit will occur between the wires.

For a wire with a section of 2,5 mm. sq. this value already reaches 25 A. As a result, the larger the cross section, the greater the throughput of the wire.

Below in the table you can see all the current values.

Now let’s tie this marking together.

For example, there is a switch with the designation B10. This means that the nominal current that the machine will pass through itself without turning on the thermal release is 10 A.

The switch has a class B, therefore, before the electromagnetic release is activated, it is able to pass a short-term current of up to 30-50 A.

But there is a small catch in this, which should be considered when choosing a machine.

For example, the current passing through it exceeds the nominal only 1,5 times. This is clearly not enough to operate the electromagnetic release.

But at the same time, if the throughput of the wire exactly corresponds to the nominal current of the machine, then the increased current value will have a destructive effect on the wire itself.

The design has a thermal release, which in the end will still work, but this takes time for the bimetallic plate to warm up and open the contacts.

And this period can be quite long, while the increased current value all this time will negatively affect the wiring.

Therefore, when choosing a machine, you should select it with a nominal value lower than the wire capacity.

So, for a wire of 1,5 mm. sq., capable of passing through itself a current of 18A, the best would be a circuit breaker with a nominal value of 10 A.

In this case, even with an increase in current strength above the rated current, the wire will pass it without possible damage.

And for a wire with a cross section of 2,5 mm. sq. and a throughput current of 25A, a circuit breaker with a rated current of 16A is suitable.

Let’s move on to the second marking – the breaking capacity of the machine. On the case, it is applied in the form of a digital designation – 4500, 6000, 10000, etc.

As already mentioned, this is the maximum current at which the machine will work without damage.

Let’s look at an example, a short circuit occurred in the network, as a result of which the current strength increased to 5000A.

The magnetic release has tripped, but an electric arc has occurred.

If the machine has a breaking capacity of 4500A, its arc chute will not be able to completely extinguish the arc of such power, and the machine itself will be damaged.

But if an automatic machine is installed, whose breaking capacity is 6000A, then its chamber will extinguish the arc, without damaging it.

In fact, this indicator is a characteristic of the security of the machine itself.

And the third marking applied to the case, and which is also important, is the current limiting class.

This marking is digital, located next to the breaking capacity marking, it consists of the number 2 or 3.

This marking indicates the speed of the machine during a short circuit. When a short circuit occurs, the current does not increase instantly, but increases.

And the sooner the machine trips, the less harm the short-circuit current will cause.

Now there are practically no automatic machines with class “2”, since they are somewhat slower than class “3” switches.

Selection errors to consider

Finally, consider the most common mistakes that are made when choosing a circuit breaker.

1 Error.

When choosing a machine, they are guided by the total power of consumers, which is one of the worst mistakes.

The machine only protects the wiring from overloads, it is unable to change its characteristics.

If you put a powerful machine on weak wiring and connect a strong consumer of energy to it, this will inevitably lead to damage to the wiring, while the machine will not be able to do its job.

Therefore, you should always be guided by the cross section of the wire and its bandwidth, and not by the power of consumers.

2 Error.

Often, all branches of the network are equipped with the same automata, and then they try to use one of the branches as a heavily loaded one.

Even at the stage of installation of the electrical network, it is advisable to make sure that at least one of the branches has increased parameters and is equipped with an automatic machine designed for significant loads.

For example, in the garage of a private house, it is possible to use devices that create a significant load.

It is better to strengthen this branch in advance than to redo it later or hope that the machine or wiring will “hold up”.

3 Error.

When purchasing circuit breakers, buyers try to minimize costs. It is better not to save on safety.

You should buy such devices only from well-established companies in specialized stores, and even better from an official distributor.

We hope that the above tips will help you choose the right circuit breaker for your home.