Frequently Asked Questions
Circuit Breakers
A circuit breaker transforms a change in an electric current into a mechanical movement that interrupts the circuit. A thermal circuit breaker does this through a bimetal element that heats up and bends; therefore, heat trips the circuit breaker.
In a hydraulic-magnetic circuit breaker, the current travels through a coil that generates a magnetic field that trips the circuit breaker. Therefore, heat is not a factor in tripping a hydraulic-magnetic circuit breaker, and this means that a hydraulic-magnetic circuit breaker is always tripped by rated current, regardless of the ambient temperature. Other benefits include smaller module sizes and lower critical resistance.
CBI has a wide variety of circuit breakers. The QF/SFM, NK and CBE products utilise the Hydraulic Magnetic technology, whereas the SFR and MCCB* ranges utilise the Thermal Magnetic technology.
* MCCB range offers a mix of Thermal Magnetic and Electronic trip units.
Yes, all CBI miniature circuit breakers (MCBs) can be reverse-fed unless they have Line/Load or +/- markings on the products.
Yes. A breaker cannot be restrained from tripping if required as a safety measure!
Even with the handle held in the ON position, the breaker will trip during an overcurrent/overload condition, safely disconnecting the load.
This feature is termed “trip free” and is contained in all relevant product specifications.
There would be no point in preventing a circuit breaker from fully functioning. It is, therefore, imperative to purchase circuit breakers from a good quality supplier known to produce a quality product.
Circuit breakers form part of essential equipment employed to keep electrical equipment safe for use!
It is per Phase.
Several factors determine the life of a circuit breaker.
For example:
- The number of normal switch operations (ON/OFF)
- Whether an electrical load current is present at the time of tripping
- Tripping on a short circuit and the level or intensity of that short circuit
- Lastly, the actual site conditions (excessive contamination dust/fumes, moisture etc.) can also significantly affect the service life of a circuit breaker.
It is important to remember that just because the circuit breaker is ON and the power is being supplied, there is no guarantee it will stay like that and, even more importantly, whether it will effectively trip when required.
Always make sure you purchase the best quality you can afford from a trusted supplier.
They are certainly not expensive if one gets a good life from them, and you can be confident they will trip when needed!
The circuit breaker’s handle can visually indicate whether an electrical fault tripped it. The handle stops in an intermediate position, between on and off, when an electrical fault tripped it.
An auxiliary switch generates a signal that indicates whether the circuit breaker is on or off but cannot distinguish whether it has been manually switched off or tripped by an electrical fault. An alarm switch generates a signal that indicates whether the circuit breaker was tripped by an electrical fault but not whether the breaker is off or turned on manually.
All units will get hot under 100% rated current. The operating temperatures could be affected depending on the cable size and the ambient temperature.
All breakers are expected to operate at 40 degree Celsius. Thermal Breakers de-rate after 40 degree Celsius, but CBI hydraulic-magnetic circuit breakers do not de-rate until 85 degree Celsius.
No, a Curve 1 breaker should always trip last in a discriminated system as it has a slower tripping curve than curve 2. Curve 1, indicated by the orange toggle on the breaker, is a slow tripping circuit breaker with a 10-20x inrush current, whereas Curve 2 has a 5-10x inrush current rating.
CBI QF/SFM products use Curve 1, Curve 2 and Curve 3 instead of D Curve, C Curve etc. The tripping curve characteristics between the curves are similar.
- A Curve 1 tripping curve will be similar to a D Curve (long time delay)
- A Curve 2 will be similar to a C Curve (medium time delay)
- A Curve 3 will be similar to a B Curve (short time delay)
