Busbar It and operating temeratures

[thood.bsec]

I have noticed that bus bar actual operating temperatures are showing as exceeding 70 degrees when design currents are less than half the bus bar rating Iz.  The software also applies a 0.86 Ct correction factor to the bus bar for 70 degree operating.

Q1: Why would the bus bar exceed its rated operating temperature before its rated It is reached when no correction factors need be applied?
Q2. Why would the software de-rate the bus bar to operate at 70?

There is lots of information on design in the Schneider catalogue including specific de-rating factors for ambient temperature and CPD type but there is no de-rating when installed in ambient of 35 or less and protected by an MCCB (my install).

[admin]

Hi,

The Ct factor only applies to the voltage drop calculations in Appendix 4 in BS767.

The software checks based on the limit specified by the user. In your case 70oC. Please see the image below too