I live on the west coast and most exterior surface mounted panel boxes have a single knockout in the back with all the branch circuits coming through, is this practice allowed per the NEC?[IMG]undefined

Is the Surface box covering an old box, or is it 1 large conduit running into the back of the box, possibly going to a Junction box?

There is only one box, it's the main breaker box and there is no conduit. The wires are all romex (NM cable) and they all come into the breaker box through a single knock out

All of them through one knockout?

No, not allowed.

Any chance you can post a photo?

I have got to see this.