Yup, absolutely. That's what I did. My heat bed uses like 30A, so I have about 8 wires grouped together for the heat bed, and 2 grouped together for the RAMPS board.
Basically, take the total amp rating of your PSU on the 12V rail, and divide it by the number of yellow wires. So if it's 30A and there are 10 wires, you'd get 3A per wire. Since your heat bed needs 11A, use at least 4 wires for that. Your board should use 5A, so use at least 2 wires for that.
Each wire should be able to carry quite a bit more current than that, but dividing it like that ensures you're not overloading them.
Basically, take the total amp rating of your PSU on the 12V rail, and divide it by the number of yellow wires. So if it's 30A and there are 10 wires, you'd get 3A per wire. Since your heat bed needs 11A, use at least 4 wires for that. Your board should use 5A, so use at least 2 wires for that.
Each wire should be able to carry quite a bit more current than that, but dividing it like that ensures you're not overloading them.
