MINIMUM ACCEPTABLE LEVELS OF SAFETY & RELIABILITY THE WIRING CODE OF TRINIDAD AND TOBAGO TTS 171...
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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
=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