# Choose the cable type

##### CHOOSE THE CABLE TYPE

Series resistive heating cables are a good alternative for longer pipe systems except for Ex-rated zones.

For frost protection can for example TCPR be used if the environment allows PVC-sheaths.

For heating-up to 180°C, use TCT/TCTR which is teflon sheathed and therefore works excellent in the most aggressive environments.

Mineral insulated heating cables are a good alternative for long pipings or when high outputs or temperatures up to 500°C shall be maintained or are obtained in a pipe system.

Take out the values according to the points below:

*Heat loss in Watt per meter, Q (W/m)
Use values calculated according to the formula

*Length of cable, L (m)
The length is made double at single wire.
Use lengths calculated.

*Supply voltage U
Find out which supply voltages are available.

*Calculate requisite cable resistance per meter
R/m = U2 /(LxQ) / L

*Choose the correct resistance value
Choose a cable, which have the calculated resistance value or the cable closest below the calculated value from the table for required type of cable.

*Sheath temperature
Always check that your calculated heating loop not exceeds the maximum sheath temperature for the cable type in question, see diagram on the data sheets.

*Calculate the current consumption of the loop
I (A) = Qtot / U (V)

*Choose cold-lead-in cable area and length.
Cold-lead-in cable is chosen in the same way as the installation cable with consideration to fusing.

*Divergent resistance as a result of high temperatures
In heating cables with high copper-bear in the heating conductor, the resistance is influenced proportionally to the temperature.

For these cables a a-value often is stated which can be put in the formula below.

 Recalculate the cable resistance with help of the formula at the required maintenance temperature R/m = R20°C a(1+(T-20))

Calculate the output, which the cable obtains at operating temperature and see if this fall below your required power. If so, choose the closest lower resistance and check calculate this.

Example:

 Q = 8,60 W/m L = 114 m U = 230 Volt P/m = 8,6 W/m Ptot = 114 x 8,6 = 980 W Tmax = 50°C R/m = 230² / 980 / 114 = 0,473 W/m

Choice of cable

Bearing the low output in mind and the relatively low operating temperature can all type of cables be used, for example series resistive PVC and teflon-cables or SRL self-limiting.

We choose TCTR 0,42 from the data sheets.

Check calculation:
P = 230² / 114 / 0,42 = 1105W
P/m = 1105 / 114 = 9,7 W/m

Leave as much information and so good description as possible when ordering.

Choosing type of cable

Projecting with parallel resistive heating cable

To be able to determine the consumption of material in an application with parallel resistive heating cable you should take out following data:

• Number of metre pipe
• Required power for the different pipes (formulas)
• Decide which cable power giving the best economy. If a piping has several different dimensions, this can be compensated of increased insulation thickness, multiple cable runs or *coiling of the cable.
• Number of valves, flanges, pumps etc.

The coiling rate is stated according to below*:

 S (Coiling factor) = Q (The required power of the pipe) P (The output/m of the cable)

Parallel resistive heating cable is used at piping systems where you require relatively low connection lengths, but not in advance can determine the exact sizes of the pipe length. At installations where the pipe has a T-branching these are carried out with a box on the exterior side of the insulation where the heating cables are connected in parallel.

VÄRMEKABELTEKNIK:s EST/CWM-cables has a layer of insulation and sheath of teflon and is available with three outputs:

 Type of cable CWM Output (W/m) Voltage (V) Max.-length (m) 12-4 CT 10/30 230/400 300/180 8-2 CT 26 230 160 12-2 CT 36 230 120

The above max. connection lengths are established on max. 10% voltage drop in the conductors. This to maintain a max. 20% power drop in the final end of the cable. (Max. connection length includes the length which can be connected from one place of connection).

The EST/CWM-cables can easily be spiralised or be installed in several cable runs to obtain required power.

Maximum process temperature, see data sheet EST/CWM.

The cables are bought in running metre and is easily completed with our connection/end termination kits on the site with help of some tongs and a hot air pistol or bottled gas burner.

Example:

 Q = 14 W/m L = 114 m U = 230 Volt P/m = 14 W/m Ptot = 114 x 14 = 1596 W Tmax = 50°C Miljö = Leakage of acid can occur

Cable choice

Bearing the low output in mind and the relatively low operating temperature can all type of cables be used, for example series resistive PVC and teflon-cables or SRL self-limiting.

We choose CWM-12 from the table above. The cable is designed in teflon, which makes it resistant in most chemical environments.

Since the heating cable emit 12 W/m we must spiralize according to the formula:

S = Q / (P/m) = 14 / 12= 1,17 m cable / meter pipe

Our cable need is then: 1,17 x 114m = 134 meter + 1 meter to connection- & end termination end.