Scribd
Upload
129 views3 pages

Exercises of Sizing Cable

An industrial process heater rated at 16kW and fed at 400V 50Hz requires a three-phase four-wire cable installation run for 25m clipped directly to a wall in a factory with a maximum ambient temperature of 35°C. Originally to be protected by BS 3036 fuses, the question considers what would be the effect on cable current rating if these fuses were replaced by BS 88 (Gg) fuses. Calculating the cable current rating using correction factors for ambient temperature and fuse protection type, a 10mm2 cable with a rating of 57A is required using BS 3036 fuses. If replaced with BS 88 fuses, the cable current rating factor would increase and a 4mm2

Uploaded by

Smida Chahinez
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOC, PDF, TXT or read online on Scribd
129 views3 pages

Exercises of Sizing Cable

An industrial process heater rated at 16kW and fed at 400V 50Hz requires a three-phase four-wire cable installation run for 25m clipped directly to a wall in a factory with a maximum ambient temperature of 35°C. Originally to be protected by BS 3036 fuses, the question considers what would be the effect on cable current rating if these fuses were replaced by BS 88 (Gg) fuses. Calculating the cable current rating using correction factors for ambient temperature and fuse protection type, a 10mm2 cable with a rating of 57A is required using BS 3036 fuses. If replaced with BS 88 fuses, the cable current rating factor would increase and a 4mm2

Uploaded by

Smida Chahinez
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOC, PDF, TXT or read online on Scribd
You are on page 1/ 3

Example

A house extension has a total load of 6 kW installed some 18 m away from the mains
consumer unit for lighting. A PVC insulated and sheathed twin and earth cable will provide a
sub-main to this load and be clipped to the side of the ceiling joists over much of its length
in a roof space which is anticipated to reach 35°C in the summer and where insulation is
installed up to the top of the joists. Calculate the minimum cable size if the circuit is to be
protected by a Type B MCB to BS EN 60878. Assume a TN-S supply, that is, a supply having a
separate neutral and protective conductor throughout.
Let us solve this question using only the tables given in the On Site Guide . The tables in the
Regulations will give the same values, but this will simplify the problem because we can refer
to Tables 7.4–7.6 in this book.

.
From column 2 of the Table 4D1A shown in Table 7.6, a 10 mm cable, having a rating of 46 A, is

required to carry this current.


(a) An industrial process heater of rating 16kW is fed at 400V
50Hz. Three-phase four-wire is to be installed in a factory using a
p.v.c.-insulated, non-armoured, copper conductors multicore
cable. Length of run is 25m clipped direct to a wall; assume a
maximum ambient temperature of 35◦C and protection by
BS 3036 fuses.
(b) If the BS 3036 fuses were replaced by BS 88 (Gg) fuses what
would be the effect on cable current rating?
Circuit details:
As it is a heater p.f. is unity.
Ambient temperature 35◦C so Ca is 0.94.
Using BS 3036 fuses so Cr is 0.725.

Using BS 7671 Table 4D2A or IEE On-Site Guide Table 6E1, from
column 7 select 10mm2 cables (57A) and using BS 7671
Table 4D2B or IEE On-Site Guide Table 6E2, column 4, read
mV/A/m value for 10mm2 cables as 3.8mV/A/m.

Using BS 7671 Table 4D2A or IEE On-Site Guide Table 6E1, from
column 7 select 4mm2 cables (32A) and using BS 7671
Table 4D2B or IEEE On-Site Guide Table 6E2, column 4, read
mV/A/m value for 4mm2 cables as 9.5mV/A/m.

You might also like