Download INTRODUCTION TO T&T WIRING CODE

INTRODUCTION TO T&T
ELECTRICAL WIRING CODE
TTS 171: PART 1: 2002
By GEORGE SAMPSON
ELECTRICAL INSPECTOR III
GOVERNMENT ELECTRICAL INSPECTORATE
What is the T&T Wiring
Code?
• Revised edition of TTS: 26 20 5051978
• REQUIREMENTS FOR THE ELECTRICAL
WIRING OF BUILDINGS AND
EQUIPMENT
• More Comprehensive
• Additional technical information.
WHO BENEFITS?
• Electrical Fraternity members
and clients
AREAS
• Designing
• Planning
• The actual installation of a wiring
system
SCOPE
• COVERS:
Installations up to 600 volts
• NOT COVERED:
Installations operated by Authorities
for
the Generation & Distribution of
electrical power such as:
 Powergen
 InnCogen
 T&TEC
ENFORCEMENT
HOW?
• The CEI is the authority with
jurisdiction
• Interpretation
• Enforcement of this standard
CONFLICT
• If ever, any conflict arises between
TTS 171 and any other standard,
the CEI shall be the sole arbitrator
and his decision shall be final
WHAT’S NEW?
The terminologies are in harmony with
international standards
Examples
2002
1978
•Ground
•Earth
•Grounding Conductor •Earth Continuity
Conductor
•Grounding Electrode •Earthing Lead (MEC)
Conductor
•Receptacle Outlet
•Socket Outlet
WHAT’S NEW ? ( Cont’d )
• Ground Fault Circuit Interrupter &
Ground Fault Protection of
equipment are also new to the list
of definitions.
ANNEX C
• Revision of TTS 1978 ( Table 21 )
• Guidelines on sub-circuit
requirements for:
• Residential
• Commercial
• Industrial Installations
• Simple Formulae and Worked
Example for voltage drop calculation (
section D.1.7.3)
• New
• It
to this standard
was included to assist with the
application of the Voltage Drop
Tables
ANNEX E
Maximum conductor fill for Conduits
& Boxes
Consider a practical case:
Install the following conductors
within a common raceway:
• 6 x 1.5mm sq.
• 8 x 2.5mm sq.
• 4 x 6.0mm sq.
• 6 x 4.0mm sq.
Comply with section 6.2.7
• A space factor of 40% is not to be
exceeded.
• The cables are not to be damaged.
• No more than two ( 2 ) 90 degrees
bends are allowed along the
conduit work.
DISTRIBUTION AND
PROTECTION
(Section 4.1.1)
• Every consumer’s installation shall
be adequately controlled by a
service disconnect. i.e. Main Switch
or Circuit Breaker
• Does this requirement apply to
systems utilizing standby power
from a Generator?
• The CEI requires that all wiring
systems are to comply with
section 4.1.1 whether they utilize
a standby Generator or not.
• In addition, those with standby
power must incorporate suitable
Transfer Equipment.
Why Transfer Equipment?
• This is to prevent the inadvertent
or accidental interconnection of
the normal (T&TEC) and the
standby ( Generator) sources of
power.
HIGHLIGHTS FROM
OTHER SECTIONS
OF THE CODE
MARKINGS
• Section 3.10.1 requires each piece
of electrical apparatus and material
to bear such markings to identify it
• To ensure its suitability for the
particular application
Examples of Markings
• Manufacturers’ name, trademark, or
other recognized symbols of
identification
• Rated load in amperes
• Rated frequency or frequency ranges
in hertz
• Whether for continuous load or
intermittent
Consequences of failure to
conform to technical data
• Persons could receive a severe electric
shock
• Explosion or fire may occur
• Serious injury may occur from a fall or
flying objects
• Electrocution is also a very, very real
possibility
The foregoing are
sufficient reasons to be
meticulous when selecting
equipment and materials.
GROUNDING ELECTRODE
CONDUCTOR &
GROUNDING CONDUCTOR
Why should we give the
Grounding Electrode
Conductor and the Grounding
Conductor the respect they
deserve?
Three basic reasons for grounding
• Limits the voltage caused by lightning, or by
accidental contact with conductors of higher
voltages.
• Stabilizes the voltage under normal operating
conditions - to maintain the voltage at one level
relative to ground so equipment connected to the
system is subjected only to that potential
difference.
• Facilitates the operation of over current devices
such as fuses, circuit breakers or relays under
ground fault conditions.
Selection and application of:
• The Grounding Electrode
Conductor and the Grounding
Conductor deserves our keenness
attention
• Sizes of grounding conductors
( Sec 9.5 )
See Current Ed. Of NFPA 70 Tables
250-66 and 250-122
APPARATUS IN GARAGES
(Section 8.5)
Where motor-driven vehicles are:
• Stored
• Serviced
• Repaired
• All apparatus shall, unless of a totally
enclosed or flameproof type, be installed
at a minimum height of 1200mm ( 4ft )
above the general floor level.
SEGREGATION OF CIRCUITS
(Section 5.23 )
• Lighting and power cables operating at voltages
above extra-low ( i.e.exceeding 50 V a.c. or
120 V d.c. whether between conductor or to
ground).
• Shall not be drawn into the same conduit or duct
as cables of extra-low voltage or of radio systems.
• Unless the latter are insulated for the higher
voltage present.
Note:
Failure to observe these
guidelines
may result in Electromagnetic
Induction (EMI ) and disruption of
the extra-low voltage equipment.
RACEWAY INSTALLATIONS
(section 6.1.1)
• Conduit works shall be completed before
any cables are drawn in.
• Ends shall be reamed and bushed to avoid
abrasion.
• Inspection boxes shall remain accessible
throughout the life of the installation.
TESTING AND INSPECTION
(Section 10 )
• To determine what malfunctions are
possible
• To determine what protection is
necessary and sufficient
• To minimize the ill-effects of such
malfunctions
Section 10.1.1
• Requires that every new installation
and
any alteration to an existing installation
shall be inspected and tested to ensure
compliance with TTS 171
Inspection and Testing
Involves:
•
•
•
•
•
Visual examination of workmanship
Verification of polarity (I.R.test)
Effectiveness of grounding
Continuity
A verification of polarity shall be made
to ensure that all fuses, circuit
breakers and single pole control
devices, are connected to live
conductors only.
Since ground fault protection relies on
operation of fuses or circuit breakers,
the resistance or impedance between the
electrode and the remote end of every
grounding conductor, shall not exceed 1
ohm.
• Where metal conduit forms part or
whole of the grounding conductor, the
above shall also apply.
Electrical Metallic Tubing ( EMT )
• Shall be protected against any risk of
mechanical damage.
• Not to be exposed to rain, dripping water,
condensation, oil, corrosive substances
and hazardous location.
• Not bend, as to damage the tubing or to
effectively reduce its internal diameter.
• Not be buried directly in the ground.
CONTROL OF MOTORS
(Section 8.12.2)
•
Each motor and its control equipment shall
have a disconnecting means.
For remote disconnecting means:
• an additional means of isolation adjacent to the
motor shall be installed OR
• a lockout device shall be installed adjacent to
the motor
•
The remote means of isolation shall be able to
be locked in the off-position.
Conclusion
Section 3.1.2 reads in part:
• This standard contains minimum
provision considered necessary
for safety, but is not to be regarded
as a design specification or an
instruction manual for untrained
persons.
THE END