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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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    Actually there is a simple way to overcome this problem, and that is to splice a short length of the bigger cable onto you 90C rated smaller size, you need enough length say 1m so that the thermal conductivity does not transfer some of the heat, and that the joint is adequately ventilated. However in this case I suspect that you are volt drop limited anyway, and the larger cable size will save its cost difference in saved electricity quite quickly. Typically such joins may be crimped or bolted crimp terminations on each cable.

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    Actually there is a simple way to overcome this problem, and that is to splice a short length of the bigger cable onto you 90C rated smaller size, you need enough length say 1m so that the thermal conductivity does not transfer some of the heat, and that the joint is adequately ventilated. However in this case I suspect that you are volt drop limited anyway, and the larger cable size will save its cost difference in saved electricity quite quickly. Typically such joins may be crimped or bolted crimp terminations on each cable.

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