NZQA registered unit standard
15855 version 5
Page 1 of 5
Title
Demonstrate knowledge of circuit protection
Level
3
Purpose
Credits
3
This unit standard is for electricians and related trades who
need to understand and select devices for the protection of
electrical circuits.
People credited with this unit standard are able to:
–
demonstrate knowledge of circuit protection terms and
principles;
–
demonstrate knowledge of circuit protection devices;
–
demonstrate knowledge of residual current devices
(RCDs); and
–
select circuit protection devices for electrical applications.
Classification
Electrical Engineering > Electrical Installation and Maintenance
Available grade
Achieved
Explanatory notes
1
This unit standard has been developed for learning and assessment off-job.
2
References
Electricity (Safety) Regulations 2010;
Health and Safety in Employment Act 1992;
AS/NZS 3000:2007, Electrical installations (known as the Australian/New Zealand
Wiring Rules), including Amendment 1;
AS 60269.3.1-2005, Low-voltage fuses - Supplementary requirements for fuses for
use by unskilled persons (fuses mainly for household and similar applications) Sections I to IV: Examples of types of standardized fuses;
and all subsequent amendments and replacements.
3
The term current regulations and standards is used in this unit standard to refer to
the requirements of the above references.
Outcomes and evidence requirements
Outcome 1
Demonstrate knowledge of circuit protection terms and principles.
The Skills Organisation
SSB Code 100401
 New Zealand Qualifications Authority 2016
NZQA registered unit standard
15855 version 5
Page 2 of 5
Evidence requirements
1.1
The meanings of circuit protection terms are explained in accordance with
industry practice.
Range
rated current, voltage rating, fusing current (fusing factor, tripping
factor), utilisation category, classes of fuses and circuit breakers,
cut-off characteristic, time vs current characteristic, category of
duty, discrimination, back-up protection, rupturing capacity
(breaking capacity), prospective short-circuit current (PSC), coarse
excess-current protection, close excess-current protection,
sensitivity.
1.2
Relationship between fusing or tripping current, current rating, and fusing or
tripping factor for a protective device is stated.
1.3
Merits of providing close excess-current protection are explained according to
current regulations and standards.
1.4
The effects of electrical faults are described in terms of the danger to people
and property.
Range
1.5
faults – leakage current, over current, short circuit;
effects – electromechanical energy, heat energy, damaged cables
and equipment, fire, explosion, electric shock.
The need for rapid disconnection of faulty circuits is explained.
Outcome 2
Demonstrate knowledge of circuit protection devices.
Evidence requirements
2.1
Protection devices are described with the aid of diagrams and reference to
construction and operating principles.
Range
2.2
Fuse cartridge type and size are identified from physical or graphical
representations of cartridge markings.
Range
2.3
devices – rewirable, cartridge and high rupturing capacity (HRC)
fuses, miniature circuit-breaker (mcb), magnetic and thermal
overload relays, fuses (including miniature glass cartridge type),
fusible links.
at least three different fuse cartridges.
Protection devices are classified according to their ability to provide either
coarse or close excess-current protection.
Range
The Skills Organisation
SSB Code 100401
rewirable fuse, HRC fuse, miniature circuit breaker.
 New Zealand Qualifications Authority 2016
NZQA registered unit standard
15855 version 5
Page 3 of 5
2.4
Time versus current curves of rewirable fuses, HRC fuses, and miniature circuit
breakers are compared in terms of speed of operation and accuracy of
calibration.
2.5
The effects of poor selection of protective devices are described for different
fault conditions.
Range
poor selection – underrated, overrated, incorrect utilisation
category, classes of fuses and circuit breakers, fusing or tripping
factor, rupturing capacity;
fault conditions – overload, short-circuit, earth leakage fault,
mechanical overload, loss of one phase in a motor, excessive
earth leakage.
2.6
A three-phase protective device is described with reference to construction,
operating principle, and protection afforded additional to that of a single-phase
circuit.
2.7
Practical demonstrations are given of resetting or reloading protective devices,
in accordance with industry practice and safety procedures.
Range
HRC fuse, rewirable fuse, mcb, thermal overload.
Outcome 3
Demonstrate knowledge of residual current devices (RCDs).
Evidence requirements
3.1
RCD terms are explained according to current regulations and standards and
industry practice.
Range
earth-leakage circuit-breaker (ELCB), residual current-operated
circuit breaker (RCCB), residual current-operated circuit breaker
with overcurrent protection (RCBO), ground-fault interrupter (GFI).
3.2
An RCD is described with reference to construction and principle of operation.
3.3
Procedures for testing the operation of RCDs are described according to current
regulations and standards.
Range
3.4
Precautions to be taken when testing circuits containing RCDs are described.
Range
3.5
operating time, residual current.
warning labels, disconnection of RCD when using a high voltage
tester, accidental tripping of RCD when testing other parts of the
circuit.
Situations requiring RCD protection are stated according to current regulations
and standards.
The Skills Organisation
SSB Code 100401
 New Zealand Qualifications Authority 2016
NZQA registered unit standard
15855 version 5
Page 4 of 5
Outcome 4
Select circuit protection devices for electrical applications.
Range
three-phase motor applications – overload, short circuit, locked rotor, phase
failure, phase reversal;
general applications – submain, subcircuit wiring, electrical accessories, singlephase appliance, outdoor appliance.
Evidence requirements
4.1
Protection device is selected to meet the application requirements in terms of
electrical protection characteristic, speed of operation, reset method, and
current regulations and standards.
4.2
Relative merits of devices are stated and compared where more than one
device meets the application requirements.
Replacement information
This unit standard replaced unit standard 755, unit standard
1207, and unit standard 1708.
Planned review date
31 December 2014
Status information and last date for assessment for superseded versions
Process
Version Date
Last Date for Assessment
Registration
1
10 February 1999
31 December 2013
Revision
2
3 April 2001
31 December 2013
Review
3
26 May 2005
N/A
Rollover and
Revision
4
15 March 2012
N/A
Revision
5
15 January 2014
N/A
Consent and Moderation Requirements (CMR) reference
0003
This CMR can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.
Please note
Providers must be granted consent to assess against standards (accredited) by NZQA,
before they can report credits from assessment against unit standards or deliver courses
of study leading to that assessment.
Industry Training Organisations must be granted consent to assess against standards by
NZQA before they can register credits from assessment against unit standards.
The Skills Organisation
SSB Code 100401
 New Zealand Qualifications Authority 2016
NZQA registered unit standard
15855 version 5
Page 5 of 5
Providers and Industry Training Organisations, which have been granted consent and
which are assessing against unit standards must engage with the moderation system that
applies to those standards.
Requirements for consent to assess and an outline of the moderation system that applies
to this standard are outlined in the Consent and Moderation Requirements (CMR). The
CMR also includes useful information about special requirements for organisations wishing
to develop education and training programmes, such as minimum qualifications for tutors
and assessors, and special resource requirements.
Comments on this unit standard
Please contact The Skills Organisation reviewcomments@skills.org.nz if you wish to
suggest changes to the content of this unit standard.
The Skills Organisation
SSB Code 100401
 New Zealand Qualifications Authority 2016