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Circuit Breaker FAQs

Circuit Breaker for Equipment (CBE)

YES, absolutely it cannot be restrained from tripping if required as a safety measure!

Even with the handle held in the ON position, the breaker will trip if an overcurrent / overload trip occurs, safely disconnecting the load.

This feature is called “trip free” and is contained in all relevant product specifications.

There would be no point in preventing a circuit breaker from full function. It is therefore very important 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!

The handle of the circuit breaker is able to visually indicate whether it was tripped by an electrical fault. The handle stops in an intermediate position, between on and off when it was tripped by an electrical fault.

  1. An auxiliary switch generates a signal that indicates whether the circuit breaker is on or off, but cannot distinguish between whether it has been manually switched off or tripped by an electrical fault.
  2. 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.

A circuit breaker transforms a change in an electric current to 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. This means that a hydraulic-magnetic circuit breaker is always tripped by rated current, regardless of the ambient temperature. Other benefits include smaller module size and lower critical resistance.

An isolator and a switch disconnnector is exactly the same thing and has the same functionality, this is simply a case of two different names for the same product.

Moulded Case Circuit Breaker (MCCB)

  • Low ambient temperatures below -5ºC
  • High ambient temperatures above +40ºC
  • Average ambient temperature per 24 hour period of  less than 35ºC
  • Relative Humidity above 85%
  • Altitude over 1000m
  •  Corrosive environments with excessive steam, oil steam, dust, salt and chemical gases.

The Under Voltage Release automatically opens a circuit breaker when voltage drops to a value ranging between 20% to 70% of the line Voltage.The operation is instantaneous, and after tripping, the circuit breaker cannot be re-closed again until the voltage returns to 85% of line voltage.

Continuously energized, the Under Voltage Release must be functioning before the circuit breaker can be closed. A CBI moulded case circuit breaker (MCCB) has the following characteristics.

  • Range of tripping voltage: 0.2 ~ 0.7 Vn
  • Reset and closing of a breaker is possible when the Control Voltage is over 0.85 Vn
  • Frequency (only AC): 45 Hz ~ 65 Hz

When a short circuit happens, the circuit breaker experiences high temperatures and high pressures. Safety clearances between the breaker, the panels, bars and other protection devices installed nearby, allow the pressure to be distributed and to prevent fire and arcing.

When installing a circuit breaker, safety clearances must be maintained. These safety clearances depend on the ultimate breaking capacity and are defined by tests carried out in accordance with standard IEC 60947-2.

Moulded Case Circuit Breakers are influenced by the external environment.  The power rating will have to be adjusted when the Circuit Breaker is used outside these standard tolerances.

  1. Ambient temperature: between -5ºC ~ +40ºC
  2. Average ambient temperature per 24 hour period:  less than 35ºC
  3. Relative Humidity: between 45 ~ 85%
  4. Altitude:  less than 2000 m. 
  5. Excessive steam, oil steam, dust, salt and other corrosive environments.

Corrections for non-standard conditions

Refer to the attached catalogue

  • High Temperatures exceeding 40ºC: refer the current correction for each level of ambient temperature in the catalogue.
  • High humidity:  the electric strength or electric performance may be degraded. Use an anti-humidty agent. Long term humidity may corrode metal parts and prevent operation.
  • Low Temperatures: Conduction, switch, trip or short circuit isolation function normally at -20ºC.
  • Extreme cold: approximately -40ºC. Refer to derating curve/s: holds more load.
  • Dust: use a dust cover.
  • Excessive vibration: may cause a nuisance trip.
  • Periods of non-use: manually switch the load current on a regular basis.
  • Corrosive gas: use sealed protection.

Low Voltage Drives

The earth leakage will sense over the 3 phases as a combined Leakage sensitivity.

The wiring standard indicates that earth leakage units should trip strictly between 15 - 30 mA. As a quality manufacturer, CBI maintains a stringent safety margin from these limits i.e. it will be a few milliamps less than 30 mA. 

Under normal circumstances, a leakage current is already present in most systems. Therefore when testing an installation and it trips well below 30 mA on your tester, that indicates that there could already be some leakage in the system.

Order Products

Use our Product Catalogue to identify an existing part by the Reorder number or "Long Code".

  • Search by product parameter, and identify the closest standard part. Then provide the Reorder number or Long code, together with any customizations.
  • The long code is a 14-28 digit number marked on the part. If you have the long code, we will have the exact product specification on file!

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