Derate XLPE cables to run to a maximum of 70 deg instead of 90 deg

Question

Hi, 
 Please can anyone tell me the best way to derate XLPE cables to run to a maximum of 70 degrees instead of 90? Thanks

Duncan Brown · Answer

Hi Martin - I'm copying your PM into here as that may assist any other users who have this same query: 
 "I'm using XLPE cable which is rated to run at a maximum temperature of 90 deg. The XLPE tables in Hevacomp state the current at the maximum running temperature of 90 deg. The equipment the cable will connect to is rated at a temperature of 70 deg therefore, I need to limit the temperature of the cable to 70deg which means it will not pass as much current; derating the cable to run at a maximum of 70deg. I can't see a setting in Hevacomp to reduce the operating/running temperature of the cable and hence the current capacity of the cable." 
 The standard cable data (that is non-manufacturer specific) is taken straight from the regulations and they only provide information for XLPE cables at 90 degrees - modifying the cable data to state 70 degrees would not change the characteristics of the cable. 
 There are two things to consider when sizing your schematic. From BS 7671:2008 : "Where cables in this table are connected to equipment or accessories designed to operate at a temperature not exceeding 70 degrees, the current rating given in the equivalent table for 70 degree thermoplastic insulated cables must be used" 
 From BS 7671:2008 amendment 3 (2015) - regulation 512.1.5 (compatibility): Switchgear, protective devices, accessories and other types of equipment shall not be connected to conductors intended to operate at a temperature exceeding 70 degree. at the equipment in normal service unless the equipment manufacturer has confirmed that the equipment is suitable for such a conditions, or the conductor size shall be chosen based on the current ratings for 70 degree cables of a similar construction. 
 Essentially this is telling us that you can consider thermoplastic cables instead, as these are rated to 70 degree. 
 This will cause an issue in that all of your reports will reference PVC instead or XLPE cables. 
 You can either provide notes to this end with your ultimate submission of the project, or you can consider the methods below to create a new cable file with XLPE descriptions, but PVC cable characteristics. Note that Bentley Systems cannot accept any responsibility for these methods or interpretation of the regulations. 
 1] Examine the PVC cables (17th Edition Menu, Cables program) and decide which cable is the equivalent to your XLPE cable. As rule of thumb, XLPE SWA M would equate to PVC/SWA/PVC, XLPE Multi to PVC Multi, XLPE Single to PVC Single. 
 2] Use the Change Cable File program

and make note of the Cable Name - do note edit anything, just note down the Cable name and click Cancel. 
 3] Now Click on the "Add new cable file" program 
 
 4] And create your new cable file with appropriate data. An example is shown here. 
 Click Ok for the next page, and provide appropriate data for this page. 
 Click ok and on the next page click on Finish. 
 5] This will have created a new cable file called (in our instance) XLPESing70 with a short name of XLPE Single 70. 
 
 Even though the cable file is created, we will have to populate it with the chosen PVC data. 
 6] Exit Hevacomp Software and use Windows Explorer to navigate into: 
 C:\ProgramData\Bentley\Hevacomp V8i\Hevacomp\IEE\Cables 
 in this folder you should be able to see our newly created "XLPESing70" file. 
 
 You should make sure you have noted down the file name, and then delete this file. 
 7] Going back to step 2, take the PVC file name that we noted down there, find this file in the folder and make a copy of this file in the same location. You should end up with something like this: 
 
 8] Rename the copied file so it reflects the filename from our new cable data file, so in this case XLPESing70 
 Once this is done, you will have a new file that has XLPE headers, but contains 70deg data, so you can use this to size your schematice in accordance the regulations. 
 I would strongly recommend making a backup of your IEE folder before starting any of this process. Best regards,