Design rule says that the overlap distance should be as follows:

5mm copper busbars- 5 times the thickness of secondary busbars

10mm copper busbars- 3 times the thickness of secondary busbars

Please see the images below:

However, IEC 61439 does not suggest that what should be overlap dimension. Temperature Rise test is the ultimate proof of joint resistance. All the joints are validated by Temperature Rise Test as per IEC 61439-1&2 in PrismaSeT I.

Released for: Schneider Electric Macedonia