By David Wren
A question that is often asked is “If I have a mixture of 70°C PVC and 90°C LSF/XLPE cables in the same installation, how can I check the operational temperature of the cables to ensure the 90°C cables are not exceeding the 70°C rating of the PVC cables?”. This is quite straightforward and can be easily checked in Wiring’s Schedules for both Sub Mains and Final Circuits, which is selected from the Display ribbon in both Sub Mains and Final Circuit modes.
In the example of a board’s Final Circuit Schedule shown below, the information relating to the cables’ temperature is in the column, Ca/Ct/Cable Op/Max Temp. Here, the last two sets of figures show, the Operational Temperature of the cable under its design conditions and the cable’s Maximum Temperature Rating.
You can use the ‘Operation Temp’ box to enter a maximum operational temperature for the cables. In this case, because of the 70°C rated PVC cables being used on Ways 1L3 & 2L3, we could set a maximum Operation Temperature of 70°C. If any cables have a maximum Operational Temperature greater than the entered value, their results in the 'Ca/Ct/Cable Temp/Max Temp' column will be shown in Red. As illustrated below.
Looking at the data for Ways 9L3 & 10L3, the cable type used here is a 90°C rated LSF. Under its design conditions it can be seen that the calculated Operational Temperature is only 75.37°C, which is well within the performance specification for this cable type, but it is also greater than the maximum temperature rating of the 70°C PVC cables also in this final board.
By reviewing the cable data here in the Schedules, you can easily see that you need to increase the size of the LSF cables on the last two Ways, to reduce their operational temperature to be less than that of the 70°C rated PVC cables.
After making the necessary size changes, you can now see the Operational Temperature of those circuits has dropped to 54.97°C. i.e. less than 70°C.
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