The purpose for the limit on HELOC loans is because of the money used for other purposes, rather than to buy, build or improve your main home. Since your debt is fully invested in your home you can deduct the full amount of the mortgage interest paid in 2017.
If you took out a loan for reasons other than to
buy, build, or substantially improve your home,
it may qualify as home equity debt. In addition,
debt you incurred to buy, build, or substantially
improve your home, to the extent it is more than
the home acquisition debt limit ($1M for 2017),
may qualify as home equity debt.
Any money from the HELOC that is not used on the home, but for other personal purposes such as a vehicle purchase or educational tuition, would be limited to $100,00 of debt. This type of use will be limited or will eliminate deduction for 2018.
