In some applications the cage is grounded. That ground is to dissipate any residual static build up on the cage metal so no one touching the cage receives a shock. But, the internal protection is still provided.

If a ground was required, why did we go through the effort to design them into space satellites and add that weight (a VERY precious commodity)? Clearly, a space craft has no general ground path. The circuit boards/layout have a positive and negative electrical path, but NOT a ground and certainly NOTHING leading from the craft into the cage to ANY component. And no long extension cord to earth.

On our boats, the static/lightning is between the clouds and the water. It will pass around the cage you make with no harm to the contents. Of course, as was said in other posts, it may go around the box and then blow out a sea cock and sink the boat.

I had 3 static engineers working for me on the spacecraft we built, one came out to our boat a few times and gave me a lot of info.

Greg