Janeyu

[Subrahmanian, Sundararaman V [IT]]

> It is yajna + upavita.  It signifies the adhikara for
> performing Shrauta
> and Smarta karmas.  Upavita means it worn draped over the
> left shoulder
> which is the position it is in when doing Devakaryas.  For
> Pitrkaryas such
> as Shraddha it is worn over the right shoulder and called
> prachinavita.

The northern direction is considered the path towards devaas and the
southern path is the path towards pitrs.  When you face east and perform
rituals, the yajnopavita is on the left shoulder and pointing towards the
north.  Since most karmas as directed towards devaas, it is normally on the
left shoulder.  When karmas are performed for pitrs, they are shifted to the
right shoulder thereby pointing to south.

- Paraphrased from "Hindu dharma"