Safety Reliability

8/18/2019 Safety Reliability

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MINIMUM ACCEPTABLE LEVELS

OF SAFETY & RELIABILITY

THE WIRING CODE OF TRINIDAD

AND TOBAGO

TTS 171 PART ONE

PRESENTED BY

• HAYDEN BATSON

• ELECTRICAL INSPECTOR 1

GOVERNMENT ELECTRICAL

INSPECTORATE


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Annex C

• Provides Sub-Circuit rating andrequirements.

• C.1 Gives the maximum sub-circuitratings for domestic, commercial andindustrial premises.

• C.2 Gives the sub-circuitrequirements.

Table C-1


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Section B gives those that are not

shown before

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.2.2

Additional 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.

• 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 of6M over road ways.

• We will maintain the IEE color code.


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INSTALLATION METHODS

The exact current carrying

capacity of conductors isaffected by a number of factors

besides CSA, one of which is the

way they are installed.

Two examples are are shownusing table D.5.D.1


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Example 1

Installing a run of 10 mm2 XLPEinsulated multi-core armored cable:

Using Method 1, a 3 or 4 core cableconnected to a 3-ph ac supply will carry

73A.

Using Method 11, a 3 or 4 core cableconnected as above will carry 78A.

Example 2

Installing a run of 95mm2 XLPEinsulated mult i-core armoured cable.

Using Method 1, a 3 or 4 core cable

connected to a 3-ph ac supply willcarry 289A.

Using Method 11, a 3 or 4 core cableconnected 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 valuesmust be observed.

VOLTAGE DROPCONSIDERATIONS

Apart from voltage drop andinstallation methods, factors such as

– ambient temperature

– grouping – thermal insulation

– operating temperature

of the cable also weigh in cableselection.


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Emphasis however must be placedon voltage drop.

WHY?

This value should not exceed 3% inthe circuit of which that cable forms

apart.

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 maximumallowable drop from the POE to

fixed current using equipmentmust not exceed 4%.

VOLTAGE DROP TABLES

These are tabulated for a

current of 1 Amp and alength of 1 Metre along the

route taken.


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For a balanced 3-ph system the

tables relate to line voltage.

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) tocarry a current of 100A from a supplyof 415V 3-ph ac, the cable being ofcopper conductor, XLPE insulated,

armoured and PVC sheathed.

Let mV be voltage drop inmillivolts

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 maxpermissible voltage drop

Then mV= 12.45 x 1000 =0.62 mV

100 x 200

Referring to the following table.

Select value = to or just less than 0.62mVi.e. 60mV.


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Apply current carrying capacity

table.

This shows that we may

have used a 25 mm2

cable without voltage

drop consideration.

THE END

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