I have a customer who is expanding into the building across the street. They are wanting to install a 6-strand fiber optic and 25-pair copper between the buildings.

In terms of cost, it better to run an aerial cable overhead or bore under the street?

If there are existing poles and or structures to which you can attach it is always going to be cheaper to go overhead. Boring is always an expensive proposition.

Keep in mind that there are a lot of factors involved such as Right of way, pole attachment permits and some areas just plain will not allow overhead cable construction.

Also you say across the street, so if they are figuring building to building they will still have to meet clearance requirements. If they go underground they still have to check on permits, all areas are different. As was stated, overhead would be cheaper, unless there is conduit between the buildings.

If I remember, overhead needs to be at least 18' above ground. Also, remember that if you bore, you run the risk of hitting other utilities like water, sewer, phone, electric...

Uncle Junkman:

The 18' rule only applies over public roads. There really aren't any rules on private roads or driveways other than those "suggested" by the NEC. Communications cables continue to fall into gray areas.