Handbook of Electrical Engineering

CABLES, WIRES AND CABLE INSTALLATION PRACTICES 239

Vrun=

√

365. 82 ( 0. 2960 × 0. 85 + 0. 0268 × 0. 5268 ) 100

415

= 7 .299%.

From (9.3) for ‘starting’ conditions,

cos Ø= 0 .45 and sin Ø= 0. 8930

Vstart=

√

3460. 74 ( 0. 2960 × 0. 45 + 0. 0268 × 0. 8930 ) 100

415

= 30 .216%.

Table 9.33 shows the volt-drop results for all the available cables.

g) Check if the earth loop impedance of the motor circuit is greater than that allowed by the fuses.

The motor circuit is shown in Figure 9.9.

Where

Vph=

415

Zloopc

Zsec= 0. 00308 +j 0 .0308 ohms/phase

Table 9.33. Volt-drop in the motor feeder cable for the

worked example

Nominal

conductor

area (mm^2 )

Running

volt-drop

(%)

Starting

volt-drop

(%)

Accept

or reject

16 7.299 30.216 Reject

25 4.733 20.492 Reject

35 3.498 15.820 Reject

50 2.672 12.792 Accept

70 1.9306 9.800 Accept

Figure 9.9 Circuit diagram for the earth loop impedance.