1. Sir, in terms of coverage under the ESI Act, 1948, and the rules/regulations framed thereunder, there is no concept of "salary" or "CTC". Only the term "wages" is relevant and important, which is defined under section 2(22) of the said Act.
2. Furthermore, the wage limit under the said Act is Rs. 15,000 per month, not below Rs. 15,000 as mentioned in your thread. (Please refer to Rule 50)