Cable amount

CALCULATING THE AMOUNT OF CABLE

Cable length

Pipe length (Llength) = m
Type of valve =
Number of valves = pcs
Flanges = pcs
Number of pipe supports = pcs

The total length of the cable needed is obtained by add the pipe length and the components.

L = Lpipe x coiling + Lsupplement
Lr = The length A is known from above
Lsupplement = (Qpipe x number of valves + factor for the type / Qcable)
+ (Number of pipe supports x 2 x pipe diameter (m) + (Number of flanges x 2 x pipe diameter (m)))

The factor for the heat loss in valves, see table on page 19.

Be sure that the cable length not exceeds the maximum recommended length, which is shown in table 3 below.

Table 3. Max. connection lengths

Cable symbol Max. connection lengths (m) at 240 V
SELF-LIMITING
RSL3
RSL5
RSL8
RSL10
RSM3
RSM5
RSM8
RSM10
RSM15
RSM20
211
166
127
109
237
228
185
149
128
106
PARALLEL RESISTIVE
CWM12-4 (10/30 W/m)
CWM8-2 (24 W/m)
CWM12-2 (36 W/m)
300/180
160
120

Series resistive teflon- and mineral insulated cables, see data sheets.

Calculate maximum circuit lengths

Fusing – self-limiting cable

Calculate the starting current with help of the formula below to determine supply cable and fusing.

Formula:

I(A) = L x Istart
L(m) = Length of cable
Istart(A) = Start current/m, see table below

Table starting current self-limiting cable

Starting currents (A/m) – Start temperature °C

Type of cable Operating temperature
-20°C 0°C +10°C +20°C
RSL-3 0,162 0,137 0,125 0,112
RSL-5 0,333 0,25 0,206 0,162
RSL-8 0,526 0,4 0,323 0,27
RSL-10 0,625 0,54 0,488 0,465
RSM-3 0,161 0,137 0,125 0,112
RSM-5 0,25 0,217 0,206 0,192
RSM-8 0,339 0,297 0,287 0,272
RSM-10 0,37 0,345 0,333 0,313
RSM-15 0,41 0,382 0,369 0,355
RSM-20 0,5 0,457 0,432 0,41

Example

Length A = 100
Type of valve = 1 claw valve
Flanges = 8
Pipe support = 8

We calculate the total length of cable.

LTot = 100 +14 = 114 meter

Lsupplement = (8,6 x 1,3/10) + (8 x 3 x 0,3) + (8x2x0,3) m= 13,11 m

We obtain a total length of 114 meter of the chosen cable SRL-5 2CR. The cable thermostat switch on the current at +40°C

The cable can be connected in one end but is then requiring a 25A time fuse due to the starting current of the cable (see table above). You can instead divide the cable in two parts in the same size and carry out the connection on the middle to 2 x 16A. This also gives a more even load of the fuses.