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What affects the operating temperature within LV switchgear
Maximum ambient condition
BS EN 60439 states a maximum indoor ambient temperature of 40ºC, a maximum daily average of 35ºC and a minimum ambient of -5ºC.
As a general guidance rule, the temperature within the low voltage switchgear should not exceed 50/55ºC. If Switchroom/Plant room ambients are typically considered to be up to 25°C this relates to a 25/30K rise above ambient. In the maximum ambient condition of 40ºC, this relates to a 10/15K rise above ambient.
Natural ventilation facilities will be required in the design of the switchboard to ensure the maximum internal temperature is not exceeded.
The sources of heat within the low voltage switchgear will be:
Heat liberated by the copperwork and cabling.
Heat liberated by the devices.
Heat liberated by eddy currents and magnetic losses.
A LV switchgear accommodates a number of devices in a configuration that relates to the scheme requirements. The enclosure and compartments within it provide the operating environment for each device.
Most devices e.g. circuit breakers, fuse switches, contactors etc. have been Type Tested in free air or “other enclosures”.
When enclosed within an LV switchgear compartment the heat liberated may adequately dissipate by convection and radiation from the “walls” of the enclosure and by heat sink via the conductors. It may however be necessary to assist the liberation to atmosphere by forced ventilation
