In article ,
Greg D. wrote:

I get a reading of 0V between the 2 hots.

That's a bad sign.

Here's my setup. I have a subpanel of 60Amps (4 x 15AMps breakers) in
my workshop. This subpanel get its current from the main panel via a
30Amps / 10-3 wire. The red and the black wires are on 2 different
15Amps breaker (in the main panel)

This sounds pretty strange too. I don't know if it's strictly against
code, but it's certainly unusual to have a subpanel fed by a 15A breaker.
Consider this scenario:

You've got a 15A breaker in the main panel, and downstream of that, you've
got several additional 15A breakers. You overload the circuit. Which 15A
breaker blows? Maybe the one in the subpanel, maybe the one in the main
panel, taking out everything in the subpanel at the same time. Like maybe
the lights?

It's also strange that somebody would run #10 wire protected by a 15A
breaker. You typically see #10 on a 30A breaker (assuming it's not a very
long run).

If everything you say is correct, I'm guessing whoever wired this stuff up
didn't really know what they were doing. I'd get a real electrician in
there to make sure things are kosher.