Do you need to install or replace a circuit breaker but are unsure which curve to choose? One-Elec helps you understand the different trip curves for circuit breakers so you can make the right choice.
What Exactly Is a Trip Curve?
A trip curve is like the personality of your circuit breaker. It determines how it will react to electrical overloads. Each curve corresponds to a different tolerance level before the power is cut off.
All electrical appliances have different protection requirements. A motor requires a lot of energy when starting up but then stabilizes. In contrast, a standard lamp or outlet maintains stable consumption from start to finish. This is why each circuit requires a specific circuit breaker curve.
The Different Curves: Each Has Its Own Use
The B curve is the most sensitive and is used for long cable runs. It is suitable for electronic devices, outlets, and public lighting. It cuts off power very quickly as soon as the current exceeds 3 to 5 times the normal intensity.
The C curve is more tolerant than the B curve. It is suitable for household appliances and small motors. It can handle current spikes of up to 5 to 10 times the nominal intensity. This type of curve is commonly used for residential installations.
The D curve is the most tolerant. It can handle spikes of up to 10 to 20 times the normal current, making it the ideal curve for large motors or industrial machinery, as they require substantial power when starting up.
The K curve is very similar to the D curve but offers more sensitive thermal protection. It provides excellent protection for cables supplying appliances with high inrush currents.
The MA curve is specially designed for motor starters. It tolerates high starting currents with a trip threshold of 12 times the rated current, without overload protection.
The Z curve is designed for controlling and protecting electronic circuits. It features a magnetic trip device that operates between 2.4 and 3.6 In. It provides very precise protection for sensitive electronic components.
How to Make the Right Choice?
The first question to ask yourself is: what appliances will I be connecting to this circuit? The answer will naturally guide you to the right trip curve for your circuit breaker.
For a standard residential installation, the C curve offers the best compromise. It protects appliances while avoiding nuisance tripping.
The choice of curve also depends on the length of your cables. As mentioned above, for circuits with long cable runs in TN systems, the B curve is more suitable.
For appliances that require substantial power (heat pumps, machinery with large motors, etc.), you should choose curve D. On the other hand, for sensitive appliances (in IT or security systems), curve B is the best choice. Its responsiveness will effectively protect your delicate equipment.
The magnetic trip threshold plays a crucial role in protecting your electrical installation. The higher you go up the curves (from B to D), the higher this threshold becomes. This feature allows you to tailor the protection to the specific needs of each circuit.
Safety First
It is very important not to overlook curves in electrical work: an incorrect trip curve can lead to unwanted and untimely power outages and, more importantly, it can be dangerous as your appliances will not be adequately protected.
Discover the selection of circuit breakers from Schneider Electric, Legrand, and ABB at One-Elec now and choose the curve that suits your needs. The important thing is to choose one that is perfectly suited to your installation! At One-Elec, a technician is available Monday through Friday to advise you if needed.
Rated Current: The Other Essential Criterion
For a well-protected electrical panel, also consider the rated current of the circuit breaker. This determines the maximum current allowed on your circuit. A 16A circuit breaker will effectively protect your appliances as long as their consumption remains below this limit. If this current rating is too low, your circuit breaker will trip continuously. If it is too high, it will no longer protect your equipment properly against overloads.
The trip curve and rated current together provide complete and effective protection.
Our One-Elec advisors are available to guide you in choosing your electrical equipment, so don't hesitate to contact them!
