4s.1.
For final circuits less than 32A the maximum operating time the protective device 0.3 when the
protective device 30A semi-enclosed fuse.2 the IEE Regulations gives the value the
prospective fault current required operate the device within the various disconnection
times given. 12.5mm2
PVC insulated copper cable
and incorporates 1.
∴ I
t
k
S
I t
k
90
0 4
115 3
2
2
A
s
(from Table )
(mm (from Regul
.
The CPC the cable greater than 0.2A.1.
S
I t
k
S
2
2
2
2
200 4
115
1 10
(mm )
( s
mm
.
Example 2
A supply feeds domestic immersion heater wired 2.
So, this case the table states that 90A will trip 15A semi-enclosed fuse 0.
a
ation 543. Verify that the 1. The
small insert Table the top right Table 3. 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 2.5(b) you can see that the time taken clear fault of
200A about 0.2.
I
V
Z
Maximum fault current (A)
A
s
∴
230
1 15
200
.3.4s.0 mm2
where mechanical protection not provided order comply with Regulation
544.
. The characteristics the protective device are given IEE
Regulation Table 3. The circuit correctly protected with 15A semi-enclosed
fuse 3036.4s.2A can seen that current about 90A will trip the 15A fuse 0.15Ω.10 mm2
found calculation.5 mm2
CPC.4s.2.49mm2
and therefore suitable.4s
from Regulation 411.
t Maximum operating time the protective device for circuit not exceeding 32A 0.
.
k 115 (from Table 54.3)
( s
mm
S
90 4
115
0 49
2
2
.3.
.Overcurrent, short circuit and earth fault protection
251
as 1.
.5mm CPC meets the requirements Regulation 543.
A 1.3. Establish calculation that the CPC adequate size meet the
requirements Regulation 543.5 mm2
CPC acceptable since this the nearest standard-size conductor above the
minimum cross-sectional area 1.2.1.5mm2
where mechanical protection provided
or 4.3).
From Table 3. From Fig
