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Under what conditions can you use Table 4E4 for cable calculations?

EVDesigner

Most LV switchgear such as Schneider Acti9, appears to be have a operating temperature of 70C . 4D4 states that I need to use 240mm2 for my submain cable run 200m through ducting to a 250A main switch. 4E4 would allow us to install 185mm2 instead at a large costing saving. We use ProDesign for verifying our cable calculations and using the BICC data sets mean that we could get a much smaller sub main size.

Does any LV switchgear have any operating temperature of 90C. I am finding this information very difficult to find on datasheets for any manufacturers.

Am I misunderstanding how the cable temperature rating relates to the switchgear operating temperature? Any help would be greatly appreciated.

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    If you have multiple installation conditions, it may be that the terminations are running at 70°C but the cable reaches 90°C elsewhere, which might relieve a constraining condition. For example, if the cables are buried in the ground, but there is sufficient exposed length in air to cool before the terminals.

    (Of course in other factors such as sheath temperature also need to be considered)

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    If you have multiple installation conditions, it may be that the terminations are running at 70°C but the cable reaches 90°C elsewhere, which might relieve a constraining condition. For example, if the cables are buried in the ground, but there is sufficient exposed length in air to cool before the terminals.

    (Of course in other factors such as sheath temperature also need to be considered)

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