MINIMUM ACCEPTABLE LEVELS OF SAFETY

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MINIMUM ACCEPTABLE LEVELS OF SAFETY RELIABILITY

• THE WIRING CODE OF TRINIDAD AND TOBAGO
• TTS 171 PART ONE

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PRESENTED BY

• HAYDEN BATSON
• ELECTRICAL INSPECTOR 1 GOVERNMENT ELECTRICAL
  INSPECTORATE

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Annex C

• Provides Sub-Circuit rating and requirements.
• C.1 Gives the maximum sub-circuit ratings for
  domestic, commercial and industrial premises.
• C.2 Gives the sub-circuit requirements.

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Table C-1
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Section B gives those that are not shown before
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C.2.1

• Ground-fault Circuit Interrupter protection shall
  be provided for personnel (ref sec 210-8 NEC
  1999) in
• a) Bathrooms
• b) Outdoor receptacles
• c) Garages
• d) Counter tops
• e) Other required locations.

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C.2.2Additional requirements for conformity.

• Receptacle outlets shall be spaced approx. 4M
  along walls in rooms.
• Receptacle outlet and lighting circuits shall be
  separated except by special permission of the
  CEI.

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• The rating for a general purpose domestic
  receptacle is 180 VA.
• The minimum height of the service entrance
  connection shall be 4M, observing the minimum
  clearance of 6M over road ways.
• We will maintain the IEE color code.

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INSTALLATION METHODS

• The exact current carrying capacity of
  conductors is affected by a number of factors
  besides CSA, one of which is the way they are
  installed.
• Two examples are are shown using table D.5.D.1

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Example 1

• Installing a run of 10 mm2 XLPE insulated
  multi-core armored cable
• Using Method 1, a 3 or 4 core cable connected to
  a 3-ph ac supply will carry 73A.
• Using Method 11, a 3 or 4 core cable connected as
  above will carry 78A.

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Example 2

• Installing a run of 95mm2 XLPE insulated
  multi-core armoured cable.
• Using Method 1, a 3 or 4 core cable connected to
  a 3-ph ac supply will carry 289A.
• Using Method 11, a 3 or 4 core cable connected to
  a 3-ph ac supply will carry 304A.

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• When using cards with current rating tables the
  method of installation for those values must be
  observed.

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VOLTAGE DROP CONSIDERATIONS

• Apart from voltage drop and installation methods,
  factors such as
• ambient temperature
• grouping
• thermal insulation
• operating temperature
• of the cable also weigh in cable selection.

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• Emphasis however must be placed on voltage drop.
• WHY?
• This value should not exceed 3 in the circuit of
  which that cable forms apart.

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• Not more than 6.90 V for a 230V 1-ph circuit
• Not more than 14.4V for a 480V 3-ph circuit.

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• Note also that the maximum allowable drop from
  the POE to fixed current using equipment must not
  exceed 4.

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VOLTAGE DROP TABLES

• These are tabulated for a current of 1 Amp and a
  length of 1 Metre along the route taken.

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• For a balanced 3-ph system the tables relate to
  line voltage.

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• Therefore the total voltage drop per run
• Vd mV x I x L
• 1000
• Where I current in amps
• L length in metres
• mV approx voltdrop/amp/metre.

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Example

• Consider a run of 200M to be installed in air
  (ref method 13) to carry a current of 100A from a
  supply of 415V 3-ph ac, the cable being of copper
  conductor, XLPE insulated, armoured and PVC
  sheathed.

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• Let mV be voltage drop in millivolts
• Then Vd mV x I x L
• 1000
• Transposing mV Vd x 1000
• I x L

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• Max permissible voltage drop 3 of 415V
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  12.45V
• Inserting values for I, L and max permissible
  voltage drop
• Then mV 12.45 x 1000 0.62 mV
• 100 x 200
• Referring to the following table.

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Select value to or just less than 0.62mV i.e.
60mV.
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Apply current carrying capacity table.
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• This shows that we may have used a 25 mm2 cable
  without voltage drop consideration.

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• THE END