Does anyone know if osha policy states that you have to lockout tagout for 50 volts or less? I can't really find it anywhere.

Well.....
I think OSHA has included NFPA 70E by reference, in 70E under 50 volts is classified as non-hazardous. In my opinion it all depends on the situation. Good safety precautions, require a lot of good old common sense. If you are working on a 24VDC transmitter, probably no tag. If you are working on a mechanical device with 24VDC solenoids, then maybe.

Again.....it all depends.

I believe the OSHA standard says you have to isolate from the hazard, they leave it up to you to determine what the hazards are.

It is only exempt from electrical hazards such as arc flash. You still must do a risk assessment. Like Ken said, if controls any type of energy such as hydraulics or pneumatics, then it would require a lockout/tagout procedure

OSHA does NOT even mention 70E by reference. There are a few cases where they spell things out. But in general, they rely on two things:

1. OSHA requires that employers provide a safe working environment (the general duty clause).
2. Providing that the company hasn't written their own procedures to do this, they will use any and all available consensus safety standards that may be applicable.

The procedure according to NFPA 70E & OSHA standards is as follows:
1. Determine the shock hazard. Result: None (NFPA 70E).
2. Determine the arc flash hazard. Result: Probably none (NFPA 70E or IEEE 1584). Hazard class zero means wear cotton only and there's no issue. You must do the calculations to verify that this is the case.
3. Are there any other hazards? If so, lock it out (OSHA lockout/tagout procedure).
4. Are you doing troubleshooting, testing, startup, taking measurements, etc., which make it impossible to complete these tasks in any way without working on the equipment live? If so, have at it (NFPA 70E) if you are wearing the appropriate PPE (items 1 & 2 on this list).
5. Anything else? Either develop a written procedure, or lock it out (NFPA 70E).

You can't just carte blanche ignore lockout/tagout because of items #3-5.

If you are disabling some function by pulling the relay, even though you might have ZERO hazards involved (items 1 & 2), and the machine is stopped and you have complete control over the operator panel (item 3), and even though it might not introduce any other hazards and you're not disabling a safety function, since it is not "troubleshooting" but actually modifying the equipment, even for this simple task that takes all of 1 second to do, item 5 kicks in and you must either go write a procedure, have briefings, etc., or lock it out, verify that the power is dead, pull the relay, and then take your lock off.

99% of what a controls/plant/electrical engineer does falls under item #4. You just get so used to working on stuff live that the tendency is to get a little cavalier about working on stuff live because that's the SOP most of the time. My example of pulling a relay is why we all tend to forget about lockout/tagout.