220v hot tub breaker to 110v

We have an old farm house , old electric box. Got a 50amp hot tub box, well it’s not being used… can I drop a 110v off it - 12-2 wire & run a line off for a treadmill? Wire neutral, white, off bar, & black off breaker side feeding hot tub? Guess I’d have 50a 110v but treadmill needs dedicated 20a. Will it be safe? Thanks for any help , guidance

Yes, if you replace the breaker.
You don’t want a 50A breaker protecting 12ga. wire - it will melt before the breaker trips.

So pull 50a & cap off other half of 220v wires & then run the one leg into a 110v 20a breaker & run from there?

It wouldn’t surprise me if the treadmill was internally fused. The OP made mention of “old farmhouse” “old electric box” and “50 amp hot tub box”. If these are all nearby, it would make the most sense to just run a new circuit, but that’s not always the easiest thing to do. What might be easiest is to turn the 50amp hot tub box in to a 20 amp fused disconnect and put two outlets next to it (one from each leg).
IOW, you probably have something like 6 or 8 gauge wire. That you want to be able to run the rest of the way with 12g, so you really should stick a 15 or 20 amp breaker in there.

Now for the tricky part, you’d be turning this into a multi-wire circuit (aka shared neutral) AND creating a sub-panel. Both of which require special considerations. If you abandon one of the hot lines, you’d get rid of the multi wire circuit part of it.

You could do what you’re suggesting, that is, replace the breaker with the proper size, abandon one wire at both ends and use the remaining hot, white and ground at the other end. I, personally, wouldn’t go that route, only because if anyone ever looks at the work, they may wonder what’s going on when they see 6awg wire spliced to 12awg wire or 6awg wire in a 20amp breaker.

Having said all that, I’ll still say, if it’s possible, just run a new circuit and don’t mess with this, you’re making it more complicated than it needs to be. If it’s in conduit and sized properly, you may even just be able to fish the wires through the existing pipe to get them over there, or at least close.

First Thanks for you input & yes starting over sounds like best route, really need updated panel, believe I’ll split out of HotTub box for now, if or when I get the opportunity to upgrade panel I can straighten it out . Thanks Again Keith B

If your hot tub box has it’s own breakers, you may be able to repurpose it. But, I’ve never looked at one very closely so I can’t say for sure. Doing so would probably make it a subpanel (I suppose it probably already is, but again, I’ve never really looked at one), so it would have to follow rules for a disconnect (namely, don’t bond the ground and neutral, but that’s probably not an issue here). You could swap out the DPST 50 amp breaker for 20amp DPST and use one hot and the neutral and ground and leave everything upstream alone. Doing that would make it easier to bring it back to the way it was should the need ever arise.

I was just going to suggest this. These days a “hot tub box” is generally a small subpanel containing a 50A GFCI breaker. If this is the case, you may (depending on the brand) just be able to replace the 50A GFCI with two separate 20A breakers (they do not need to be double-pole since they are no longer running to the same circuit). If the treadmill is in unfinished space or outdoors then you either need a GFCI breaker or a GFCI outlet. The grounds and neutral in the hot tub box should already be separated (assuming the box was installed properly).

The only reason, in my scenario, I suggested keeping the 2 breakers as a single DPST breaker was because of the potential of setting up a shared neutral situation which requires both breakers on the multi-wire circuit to be tied together so they both get shut off at the same time.

Look at it this way. The OP is, essentially, borrowing all the conduit and wires, for the sake of convenience, from the breaker box to this sub panel. If he decides to do the same from here to where the hot tub was, and put the outlets there, he’d have two hots (on different legs) and one neutral which comes with a certain set of dangers. I was just trying to mitigate some of that (it also brings it up to (2011) code).
I still suggest running a new circuit or if the hot tub wiring is in EMT, pulling it out and pushing/fishing the correct wires though it and using the right breaker and outlet (and outlet box). Then it’ll be correct and not look like it was hacked together.