After extracting a 7z file I've noticed its split into 2 bin files instead of 1.

I actually extracted two, one split into 612 and 36mb and the other one 617 and 36mb.

The first one runs ok but obviously eventually this will cause problems. Is this normal and how do I get around it?

Thanks in advance.

Those are redump images. If it is just one .bin file you can use it with pcsxbox. Multiple .bin files however are games with CDDA tracks.

You'll need to either wait until the next release of pcsxbox (which supports redump) or mount those images in a CD image program (like Alcohol 120%) and create a ".bin/.cue" combo file from that.