### TTS 171 : PART 1: 2002 - Faculty of Engineering

```TTS 171 : PART 1: 2002
ANNEX E
PRESENTER
WINSTON THOMAS
ELECTRICAL INSPECTOR 1
MAXIMUM CONDUCTORS IN
CONDUIT AND BOXES
• Objective
• Simple guide
• Calculation
Cont’d.
• Maximum number of cables
• Conduits
• Boxes
CONDUITS
• Electrical Metallic Tubing or
E.M.T
• Steel heavy gauge conduit
• PVC conduit
APPLICATION
• Surroundings
• Ambient temperature
• Level of mechanical
protection
CAPACITIES
• For the maximum capacities
• Reference to Annex E
• Relevant table
TABLES IN ANNEX E
•
Four tables
• Maximum PVC insulated
non sheathed cables
• Space factor of 40 %
Cont’d.
• Two
0
90
bends
• Cables reduced
USE OF TABLES
•
Calculate number of cables
for circuit
Choose cable size in column
 Use maximum number of
cables column
Cont’d.
 Choose value equal to or
greater than number of
cables
 Go to corresponding column
for conduit size
TABLE E 2a
 Covers maximum capacities
 Steel conduit and E.M.T
• PVC insulated non-sheathed
single core cables
Cont’d.
• Same cross-sectional area
• Imperial, AWG or MCM
and Metric sizes
Example
A 115/230V single phase a.c
circuit requiring 16mm2 single
core cables is to be run in an
E.M.T conduit .
To determine conduit size.
Calculate Number of cables. (3)
Cable size column. (16mm2)
Maximum number cables
column. (4)
Corresponding conduit size
of 27 mm or (1 in).
Table E 2b
• Covers maximum capacities.
 Steel heavy gauge conduits.
 PVC insulated cables of
same cross-sectional area.
Example
Using three 16mm2 cables as in
the previous example.
Conduit size approximately the
same.(25mm)
Table E 2c
• Covers maximum capacities.
 PVC conduits
 PVC insulated cables of same
cross-sectional area
Example
Same circuit to be run in PVC
conduit.
A grounding conductor is now
required.
Number of cables. ( 4 )
Cont’d
Maximum number of cables
column. (5)
Conduit size - 32mm
Table E1
• Covers maximum capacities.
• All types of conduits.
Cont’d
• PVC insulated cables of
different cross-sectional
areas
• Conduit factor
• Conductor factor
Example
Four 2.5mm 2 , four 4.0mm 2 and
two 6.0mm 2 cables, are to be
drawn into a conduit.
Total conductor factor = Sum of
cable conductor factors.
Cont’d.
Conduit factor shall be equal
to or greater than total
conductor factor.
4 x 2.5mm 2 factor = 4 x 30 = 120
4 x 4.0mm2 factor = 4 x 39 = 156
2 x 6.0mm2 factor = 2 x 50 =
100
Total
376
Conduit factor - 486
CAPACITIES OF BOXES
Table E 3
• Maximum capacities.
• Outlet and junction boxes
Example
2
4.0mm cables
Sixteen
spliced in a box.
to be
Determine size of box.
First go to column for 4.0mm
Cont’d.
Then to row where value is
equal to or greater than
sixteen.
Then to box in corresponding
row. (4 11/16 x 2 1/8)
THE END
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