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CIRCUIT PROTECTIVE DEVICES
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CIRCUIT PROTECTIVE DEVICES
A circuit protective device is designed to provide protection against the various types of overcurrent, such as overload, short circuit and earth fault.
TYPES OF CIRCUIT PROTECTIVE DEVICES INCLUDE:
1
FUSES: A. High Rupturing Capacity (HRC) or High Breaking
Capacity (HBC) fuses: These are designed to handle very high fault currents, as they have a high breaking capacity, and are manufactured in a range of nominal ratings from 3A to 500A.
B. Plug-Top Fuses: Found in every 13A plug-top or fused connection unit, ranging from 1A to 13A.
C. Semi-Enclosed Fuses: Often called rewireable fuses, these are now often replaced by circuit-breakers.
D. Cartridge Fuses:
Similar to HRC fuses and often found in consumer units, these are intended for use by ordinary persons so are common in residential installations.
2CIRCUIT-BREAKERS:
Circuit-breakers are probably the most frequently used protective devices and they are available in one of the following formats:
Cartridge fuse for household 10A MCBs
A. Miniature Circuit-Breakers (MCBs):
These devices are often used as protection for final circuits and come with nominal ratings between 3A and 125A.
B. Moulded Case Circuit-Breakers (MCCBs):
These are larger circuit-breakers, generally used in the large panel boards that protect distribution circuits.
3CIRCUIT-BREAKERS HAVE TWO FORMS OF OPERATION:
● Via a magnetic trip: A solenoid within the circuit-breaker where a pre-set value of overcurrent creates a magnetic field strong enough to instantly disconnect the device.
● Via a thermal trip: A slightly longer process, where an overcurrent heats up a thermal device, such as bi-metallic strip, causing disconnection.
THERE ARE 3 TYPES OF MINIATURE CIRCUIT-BREAKER:
● Type B: These would typically be used to protect lighting and socket circuits where sudden over-currents do not occur during switching.
● Type C: These would typically be used in commercial and industrial environments, to protect loads that surge on starting, such as discharge lighting or motors.
● Type D: These should only be used on very specialist loads, where high inrush currents may be expected, such as transformers, x-rays and welding sets.
RESIDUAL CURRENT DEVICES (RCDS):
RCDs are different from circuit-breakers as they do not provide short-circuit or overload protection. They are often built into wiring accessories, such as socket outlets and fused connection units, and are incorporated into consumer units as an RCCB or RCBO.
RCDs monitor the current passing through the device into the circuit (live) and the value coming back (neutral). If these values are different, some current must be escaping to earth. If the difference between the values on either side, i.e. live and neutral, is bigger than the residual operating current setting, the device will trip.
RCD Residual Current Device
4RESIDUAL CURRENT CIRCUIT-BREAKERS WITH INTEGRAL OVERCURRENT PROTECTION (RCBOS):
An RCBO is a circuit-breaker that also has an RCD built into it, giving it overload, short-circuit and residual earth current protection. RCBOs fitted for circuit protection require a neutral connection as well as the live, because they need to monitor the individual circuit current for imbalances.
WHAT IS AN ARC FAULT?
Where the electrical current jumps between two conductive materials.
PARALLEL ARC FAULT SERIES ARC FAULT
The most common causes of arcs include worn contacts in electrical equipment, damage to insulation, break in a cable and loose connections.
HOW DO ARC FAULTS OCCUR?
Kink/break in the cable Cable wear due to frequent use
Incorrect bending radii Loose scewed connections
HOW DOES AN ARC FAULT DETECTION DEVICE (AFDD) WORK?
They use microprocessor technology to analyse the waveform of the electricity being used to detect any unusual signatures which would signify an arc on the circuit. This will cut off power to the affected circuit and could prevent a fire. They are far more sensitive to arcs than conventional circuit protective devices.
Line damage resulting from drilling or construction work Incorrect wire stripping
Defective plugs Rodent bites
AFDDs use an algorithm to identify Arc Faults. New advanced electrical items which are introduced to the market may demonstrate different electrical signatures from devices today.
THE LAUNCH OF AFDD WITH PROTOOLS
Changing the Game with the launch of AFDD with ProTools diagnostics software.
Equipped with built-in advanced diagnostics software, once the Hager RCBO/AFDD or MCB/ AFDD device has tripped, installers can quickly identify the cause for the disconnected circuit at the push of a button on the front of the device.
The multicoloured LED display will flash in a different sequence of colours to identify the fault. With the ability to identify 8 statuses, the device will instantly detect if a Series Arc, Parallel Arc, Overvoltage, Residual Current Fault, Overload, Short Circuit, AFDD failure or manual trip has occurred, saving time and improving diagnostic ability.
Whilst the extensive testing program provides a stable platform for today, it is possible that an electrical goods manufacturer of tomorrow may create an electrical device with a different waveform signature, thus creating a new signature for the Arc Fault Device and causing the device to trip.
With ProTools and in-situ software upgrades, Hager is able to modify the algorithm to accommodate new product signatures. These updates can be sent directly to installers’ mobile devices, via the Hager Pilot app, allowing them to connect to the AFDD through Bluetooth technology and perform a software upgrade.
Neutral in (flying lead)
D/RCD function
HAGER AFDD WHAT’S INSIDE
Rogowski coil (AFD function)
Arc Chamber
Differential toroid (RCD function) Magnetic coil
LED Indicator
Bimetal blade (thermal function)
For more information, visit www.hager.com
