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.