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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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    It rather depends on the additional correction factors for grouping, routing and burial and so forth - the switch gear may be well ventilated and the cores of the wire well separated so at 70C or lower, while  the cable rating is set by part of the cable further along that is grouped, or buried, or in some other way not optimally cooled. Or indeed in reverse you may step up a cable size for the last metre of cable in the switch room if the cooling there is especially awful due to grouping etc.
    On a 200m run however, I'd want to check that volt drop may restrict  the cable size rather than heating. (or leave no allowance for VD in the later wiring.)
    Mike.

    edit sorry composed this at the same time so cross-posted/

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  • 0

    It rather depends on the additional correction factors for grouping, routing and burial and so forth - the switch gear may be well ventilated and the cores of the wire well separated so at 70C or lower, while  the cable rating is set by part of the cable further along that is grouped, or buried, or in some other way not optimally cooled. Or indeed in reverse you may step up a cable size for the last metre of cable in the switch room if the cooling there is especially awful due to grouping etc.
    On a 200m run however, I'd want to check that volt drop may restrict  the cable size rather than heating. (or leave no allowance for VD in the later wiring.)
    Mike.

    edit sorry composed this at the same time so cross-posted/

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