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Inter Terminals Ltd. - Tyne Terminal
Tank 24 Road Loading Overspill System – I.S. Calculation
P & I Design Ltd
DOCUMENT NO: 16115CAL001
2 Reed Street, Thornaby, UK, TS17 7AF
ISSUE: A
Tel: + 44 (0) 1642 617444
DATE: 02/02/17
Fax: + 44 (0) 1642 616447
PAGE: Page 8 of 8
www.pidesign.co.uk3.4
Cabling
The following cable descriptions, obtained from SI347100.SCH and SI347001_DWG were
used to select the cable’s electronical data:
A 10-pair individually screened cable with an area of 1.5mm
2
, connecting the
isolator and the junction box.
A 2-pair collectively screened cable with an area of 1.5mm
2
, connecting the
junction box and the sensor.
The standard approach to performing the intrinsically safe circuit calculation is to use cable
data from BS 5308 based on the number of cable pairs, the type of screening and the
conductor size. The data has been summarised below:
Conductor
Size
L/R Ratio
(maximum)
Maximum mutual capacitance
Resistance
Cables
without
screens
Cables with
only
collective
screens
(except one
pair and two
pair)
One pair and
two pair
cables
collectively
screened and
all cables with
individually
screened pairs
0.5 mm
2
25 µH/Ω
75 pF/m
75 pF/m
115 pF/m
13.7 Ω/km
1.0 mm
2
25 µH/Ω
75 pF/m
75 pF/m
115 pF/m
18.4 Ω/km
1.5 mm
2
40 µH/Ω
85 pF/m
85 pF/m
115 pF/m
12.3 Ω/km
Table 2: A Summary Table from BS 5308. Yellow highlighting shows data used.
Note that:
The same data is suitable for both cables.
The inductance value used in 16115CAL002 and 16115CAL003 is the product of
the L/R Ratio and the Resistance.