Overcurrent, short circuit and earth fault protection
251
as 1.5mm2
where mechanical protection provided
or 4.
k 115 (from Table 54.3.10 mm2
found calculation.3. The characteristics the protective device are given IEE
Regulation Table 3.
a
ation 543.4s. From Fig.
∴ I
t
k
S
I t
k
90
0 4
115 3
2
2
A
s
(from Table )
(mm (from Regul
.5mm CPC meets the requirements Regulation 543.5 mm2
CPC.2.3)
( s
mm
S
90 4
115
0 49
2
2
.
From Table 3.
.2.
.1.49mm2
and therefore suitable.1. Verify that the 1.
.2A.
S
I t
k
S
2
2
2
2
200 4
115
1 10
(mm )
( s
mm
.4s.5 mm2
CPC acceptable since this the nearest standard-size conductor above the
minimum cross-sectional area 1.2 the IEE Regulations gives the value the
prospective fault current required operate the device within the various disconnection
times given.3 when the
protective device 30A semi-enclosed fuse.
The CPC the cable greater than 0.3).1. The
small insert Table the top right Table 3.
t Maximum operating time the protective device for circuit not exceeding 32A 0.
A 1.
So, this case the table states that 90A will trip 15A semi-enclosed fuse 0. the protective
conductor separate conductor, that is, does not form part cable this example
and not enclosed wiring system Example the cross-section the protective
conductor must not less than 2.2A can seen that current about 90A will trip the 15A fuse 0. The circuit correctly protected with 15A semi-enclosed
fuse 3036.4s
from Regulation 411.5(b) you can see that the time taken clear fault of
200A about 0.4s.4s.
.15Ω.
Example 2
A supply feeds domestic immersion heater wired 2.
For final circuits less than 32A the maximum operating time the protective device 0. Establish calculation that the CPC adequate size meet the
requirements Regulation 543. 12.
I
V
Z
Maximum fault current (A)
A
s
∴
230
1 15
200
.5mm2
PVC insulated copper cable
and incorporates 1.2.0 mm2
where mechanical protection not provided order comply with Regulation
544.3
