TTS 171 : PART 1: 2002

ANNEX E

PRESENTER

WINSTON THOMAS

ELECTRICALELECTRICAL INSPECTOR 1INSPECTOR 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

• Surroundings

• Ambient temperature

• Level of mechanical

protection

APPLICATION

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 900 bends

• Additional 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.

Follow same steps.

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

• New addition to code.

• Covers maximum capacities.

• All types of conduits.

Cont’d

• PVC insulated cables of different cross-sectional areas

• Conduit factor

• Conductor factor

.

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.

Example

Cont’d.

Conduit factor shall be equal

to or greater than total

conductor factor.

4 x 4.0mm2 factor = 4 x 39 = 156

2 x 6.0mm2 factor = 2 x 50 = 100

Total 376

Conduit factor - 486

Conduit 27mm ( 1 in. )

4 x 2.5mm 2 factor = 4 x 30 = 120

CAPACITIES OF BOXES

Table E 3

• New addition to code.

• Maximum capacities.

• Outlet and junction boxes

Sixteen 4.0mm2 cables to be

spliced in a box.

Determine size of box.

First go to column for 4.0mm

cables.

Example

Cont’d.

Then to row where value is equal to or greater than sixteen.

Then to box in correspondingrow. (4 11/16 x 2 1/8)

THE END