Variable Rate HELOC question

[Alex Lloyd]

When using a HELOC with a variable rate, when you take out a loan against your credit line, are you "locked in" to that rate for the entire amount you have to pay back on the amount of money you took out, OR do fluctuations in the prime rate also apply to money you've already taken out?

To help illustrate my question with a couple scenarios:

1. - You take out a HELOC with a $120,000 limit and borrow $50,000 for a down payment, closing costs etc. on an investment property. Will your interest rate:
   1. be fixed at the rate of whatever the prime rate was whenever you took out the $50,000 for however long it takes you to repay the $50,000 OR
   2. will the $50,000 you withdrew be subject to prime rate fluctuations (or is it just the remaining $70,000 of the $120,000 limit that is subject to prime rate fluctuations, since you already withdrew the $50,000 and are "locked in to the interest rate of whatever the prime rate was when you withdrew the $50,000)?

I'm sure there was a much easier way to ask this - just want to be clear on the ask, and appreciate any help here!