Wire carts and caddies hold spools of electrical wire of various sizes to make pulling wire easy. Both are designed to hold electrical wire mounted on spools. These spools of wire vary in length an physical size.
Notice in the photo of the wire cart, just a few different sized reels of wire that can easily be mounted on the wire cart. The cart can hold the smaller 500' reels and also 1000' reels. Wire is mounted on steel rods that slide through drilled holes on the sides of the mounting frame. This cart has wheels to make positioning the cart easy. The cart incorporates a large foot that keeps the cart from tipping over when you are pulling the wire from the cart. By simply pulling the pins and sliding the steel rods to the side. reels of wire can be added to the cart. Try to have all of the wire either pull off of the top or bottom of the reels. That way, the reels won't fight each other when you are pulling the wires.
Wire caddies hold smaller reels of wire. These reels come in 500'lengths and can easily be added by removed by pulling the pin and sliding the steel rod to the side. Place up to four reels within the caddy and slide the rod through the wire reels. Replace the pin and insert the wire through the wire slots located in the handle assembly. These dividers keep the wires from getting crossed and tangled. The handle comes with a handle to make carrying the caddy easy. This is great for smaller jobs that a couple of circuits are needed. You can easily put wire on the caddy to pull two hot wires, one neutral wire , and a ground wire. This network of wires will make pulling circuits in a home very convenient.