@Lynn Maher --yes, $50k is the max, but not per year. That $50k is an absolute maximum.
The actual IRS calculation is the lesser of: 1) 50% of your total vested balance, or 2) $50,000 minus the highest outstanding loan balance over the past twelve months. So....
If your vested balance is $80,000, you can take a loan out for $40,000 (assuming your employer or the plan doesn't restrict any sources of money). If your vested balance is $200,000, you can still only take a loan out for $50,000. And if you take out a $50k loan on Oct. 20, 2014, and have a $48,000 balance on Jan. 1, 2015, you can't take another $50,000 out.
Also, to emphasize another point I made above, the second half of that IRS calculation can be tricky. Let's say you take out a loan for $50,000 to buy a flip, you do the rehab and sell it in four months, then pay back the $50,000 loan. You won't be able to take another loan out for another eight months because the IRS calculation is seeing that "highest outstanding loan balance over the past 12 months" as $50,000, and according to the calculation, $50,000 minus $50,000 equals zero. Or say you take a loan out for $35,000 and pay it back in six months; over the next six months your maximum loan amount might be $15,000.
And again, to kick a dead horse another time or two, THIS IS ALL EMPLOYER SPECIFIC. I have seen one employer that only allowed you to borrow 25% of your vested balance.