Then, its main busbar circuit requirement current is 1620 A (2700 A * 0. The IEC 61439-1 sets the thermal limit in busbars working at the maximum working load. Here, 140°C (which is 105K over the ambient temperature of 35°C) is the upper safe temperature limit. To find the busbar current, multiply the width & thickness together, then multiply by the material carry capacity factor. With the aid of a correction factor (k2), the continuous currents specified in the follow-ing table may be adjusted to alternative oper-ating temperatures. Unlike cables, a busbar has a defined rectangular or tubular.