by David Wren
Although the cables types XLPE, LSF, LSZH etc are 90°C rated, the terminals of switchgear and distribution boards they are connected to are quite often only rated at 70°C. Or, if an older existing electrical distribution network is being upgraded and the old in-situ cables pass Inspection and Test, you could well be installing newer XLPE or LSF single or armoured cables alongside older 70°C rated PVC cables.
For compatibility in compliance with Regulation 512.1.5, the newer 90°C rated cables should be so designed that at their maximum design load, their operational temperature does not exceed 70°C. This can already be checked in the Sub Mains and Final Circuit Schedules. In this extract from the schedules, you can see the two circuits using LSF 90°C cables are running too hot for the adjacent circuit using older PVC 70°C rated cable.
There is now new a new function in MEPworx 2023 to allow this to be set globally for the whole project.
In the MEPworx Defaults Editor which is accessed via the Utilities tab on the front screen, select the Wiring program at the bottom of the pull-down list. Next scroll down to the line for MaxTempFactor. You will see here that the default is set to 0.7777.
This is derived from 70/90 to take account of 70°C rated equipment being used in the project. If you would like to set your projects up for 90°C operation, simply change this value to 1.00.
Or, if for example, you are designing the distribution for a Petrochemical plant and want to limit the maximum operational temperature of the cables and switchgear to say 50°C. Take 50/90 = 0.5555.
If this value is then entered into the MaxTempFactor entry of the Defaults Editor (remembering to Save the changes), any cables in your Wiring project that exceed the 50°C maximum operational temperature, will display a new warning message.
Please note. When this value for different temperatures is edited, it will apply to all wiring projects visited and should be reviewed for each project as required.