Relation between Current Carrying Capacity of Bus Bar Trunking (BBT) and Ambient Temperature

Ambient Temperature

Ambient Temperature is basically known as the room temperature of any environment.

Relation Between Current Carrying Capacity and Ambient Temperature

In one sentence, the current carrying capacity of BBT is inversely proportional to the ambient temperature.

So that, A correction factor has to be applied for temperature higher than 35 °C. The correction factor application is provided by the Busway manufacturer.

Example

For Schneider electric medium and high power range (Up to 4000A) the correction factor is given in the below table:

°C	35°C	40°C	45°C	50°C	55°C
Correction factor	1	0.97	0.93	0.90	0.86

Reff: Product Catalog of Schneider Electric BBT 

That means;

In-room temperature (35°C), A 400A BBT will carry 400 A in full load.

In increased temperature (40°C), A 400A BBT will carry 400A X 0.97 = 388A in full load.

In increased temperature (45°C), A 400A BBT will carry 400A X 0.93 = 372A in full load.

And So On.