The question is, are belts allowed in “Raw” powerlifting meets - the answer to which is a resounding yes. While not all lifters have to necessarily wear a belt during their powerlifting meets most federations (if not all) allow lifters to have some sort of powerlifting belt at their meets. To understand why you won’t see a federation (yet) that doesn’t allow powerlifting belts (*here's how to choose a proper powerlifting belt) during meets, you must understand the purpose that powerlifting belts serve.
What are powerlifting belts used for
For starters, we need to clear up a few myths regarding powerlifting belts. First, they are not going to add 100 lbs. to any movement. Powerlifting belts are supportive but just not in the way that you think. Powerlifting belts/Braces basically help lifters stay tight and increased core and spine stability. So, yes it helps you keep your spine neutral during the squat and deadlift (as well as during other movements like the Overhead Press) and keep your spine from rounding during heavy deadlifts (if you're wondering how often you should perform heavy deadlift this article will help) - which can be the difference between a herniated disc and a healthy spine.
What exactly is happening when you use a powerlifting belt?
Another myth that lifters tend to attach to the name of powerlifting belts is that take the place of your abdominal strength and are all you need to lift heavy-weight. That’s not true whatsoever. Your powerlifting belt acts as backup to your core (by giving you something to brace against). When you use a powerlifting belt you’re pushing against it so that you’re able to stabilize your spine and core muscles. The biggest thing to remember here is that the function of breathing in and pushing against the belt is what’s keeping you healthy during loaded movements. It also helps you keep from leaking energy during any of your lifts which is great for lifting weight efficiently.
*leaked energy comes from not being able to hold your form during your lifts. Also, keep in mind that belts don't store any elastic energy - it just helps you stay tight
So, why are they allowed at Raw competitions?
Unlike the primary function that supportive bench shirts, wraps, and other things serve, powerlifting belts help lifters keep a healthy spine during all weighted movements and, they don’t really add much weight to your lifts. The most I’ve seen a belt add to a lift like the squat or deadlift is 30 lbs (a decent number but, not enough to really be considered equipped lifting). In fact, there are actually some people who say that powerlifting belts don’t add anything (or takes away from) their numbers on certain lifts - take this with a grain of salt as they probably just haven’t found a powerful position for the movement.
Here's a great book that explains the benefit of wearing a belt in more detail.
* if you want to know which federations are actually raw, read this article
What’s the legal size for a powerlifting belt?
In general, the cutoff thickness for a powerlifting belt is 13mm and the cutoff width is about 10 cm or about 4 inches. Any more than this and a powerlifting belt can quickly become either a hindrance or an overly supportive device that’s basically doing all of your lifting for you. Also keep in mind that having a belt that is too thin or flimsy will likely not do your lower back or core any good. *having a belt that’s less than 8mm in thickness will just force your core to all of the work. And if that’s the case you may as well lift without your belt.
Conclusion
In conclusion, yes, powerlifting belts are allowed in raw powerlifting. They give the core something to brace against and make the act of lifting heavier weights more bearable on the lower back. Also, yes, they will very likely increase your weight lifted on lifts that are core reliant like the deadlift and squat. As long as your belt is completely legal (10 cm in width and 13 mm in thickness) you will be able to use it at your powerlifting meet (regardless of who is sanctioning it).
Resources:
https://www.t-nation.com/training/do-you-really-need-a-lifting-belt
https://www.bodybuilding.com/content/3-key-benefits-of-wearing-a-weightlfting-belt.html
https://startingstrength.com/resources/forum/general-q-and-a/17784-weight-lift-belt.html