INTRODUCTION TO T

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INTRODUCTION TO TT ELECTRICAL WIRING CODETTS
171 PART 1 2002

• By GEORGE SAMPSON
• ELECTRICAL INSPECTOR III
• GOVERNMENT ELECTRICAL INSPECTORATE

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What is the TT Wiring Code?

• Revised edition of TTS 26 20 505-1978
• REQUIREMENTS FOR THE ELECTRICAL WIRING OF
  BUILDINGS AND EQUIPMENT
• More Comprehensive
• Additional technical information.

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WHO BENEFITS?

• Electrical Fraternity members and clients
• AREAS
• Designing
• Planning
• The actual installation of a wiring system

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SCOPE

• COVERS
• Installations up to 600 volts
• NOT COVERED
• Installations operated by Authorities for
• the Generation Distribution of
• electrical power such as
• Powergen
• InnCogen
• TTEC

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ENFORCEMENT

• HOW?
• The CEI is the authority with jurisdiction
• Interpretation
• Enforcement of this standard

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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

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WHATS NEW?The terminologies are in harmony
with international standards Examples
2002 1978
Ground Earth
Grounding Conductor Earth Continuity Conductor
Grounding Electrode Conductor Earthing Lead (MEC)
Receptacle Outlet Socket Outlet

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WHATS NEW ? ( Contd )

• Ground Fault Circuit Interrupter Ground Fault
  Protection of equipment are also new to the list
  of definitions.

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ANNEX C

• Revision of TTS 1978 ( Table 21 )
• Guidelines on sub-circuit requirements for
• Residential
• Commercial
• Industrial Installations

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• Simple Formulae and Worked Example for voltage
  drop calculation ( section D.1.7.3)
• New to this standard
• It was included to assist with the application of
  the Voltage Drop Tables

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ANNEX EMaximum 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.

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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.

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DISTRIBUTION AND PROTECTION (Section 4.1.1)

• Every consumers 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?

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• 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.

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Why Transfer Equipment?

• This is to prevent the inadvertent or accidental
  interconnection of the normal (TTEC) and the
  standby ( Generator) sources of power.

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• HIGHLIGHTS FROM OTHER SECTIONS OF THE CODE

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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

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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

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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

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• The foregoing are sufficient reasons to be
  meticulous when selecting equipment and materials.

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GROUNDING ELECTRODE CONDUCTOR GROUNDING
CONDUCTOR
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• Why should we give the Grounding Electrode
  Conductor and the Grounding Conductor the respect
  they deserve?

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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.

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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

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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.

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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.

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Note

• Failure to observe these guidelines
• may result in Electromagnetic
• Induction (EMI ) and disruption of
• the extra-low voltage equipment.

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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.

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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

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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

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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.

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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.

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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.

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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.

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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.

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• THE END