Portuguese to English Tech/Engineering Transport / Transportation / Shipping General rail and metro construction

caixa de bondeamento

I have no other reference to this word in the doc and it does not appear to be a real word. The only other occurrence I found is in this doc below. It looks like it has something to do with earthing the rails or ensuring electrical continuity and prevention of galvanic corrosion but what is a caixa de bondeamento ??

http://www.brastan.com.br/wp-content/uploads/pin-braing.pdf