I have a finished two-story house which has two interior walls vertically stacked.

I'd like to run ethernet from the top floor to the bottom, by:

  • cutting out a square for a wall plate on the top floor
  • use a flexible installer bit (3') to drill through the bottom plate of the top story frame via the small access hole of the wall plate.
  • continue downward and drill through the top plate of the bottom floor frame (still inside the wall)
  • drop the wire down inside the wall to the plate on the bottom floor (no fireblock in the wall)

This allows me to run the cable with no drywall repair.

However, the space between the floors is unknown to me. The long flexible bit allows for drilling through places where you cannot reach or see, so I can't be sure there's nothing between the floors that could be damaged by the drilling.

How do professionals safely use this long bit and avoid hitting joists, electrical lines, pipes, etc.?

I thought about a borescope but I'm not sure if I could stop the drill before hitting something after punching through the first bottom plate, if there was anything directly beneath it.

Picture of scenario: http://www.licensedelectrician.com/Store/ET/Images/Tip2.jpg

2 Answers 2


Select a location between studs where the space does not contain any electricial devices, and it seems that it would not contain pipes devices.

Drill through the top plate with a larger drill bit, of 'standard' length.

Put a dowel, or single piece of solid wire in the hole until it touches the bottom.

Tap both walls and both studs in the space while you slowly pull the wire up, checking for things in the way.

Put the long bit in the hole, by hand, off the drill, checking for any resistance while lowering the bit.

Put the drill on the bit.


Run wire.

This has worked 99 of 100 times for me. The 1 time I miss, really sucks.

Best of luck

  • 2
    Thanks. Might I ask how this failed the time you got unlucky?
    – Tim
    Apr 4, 2015 at 15:41

Some cowboy it and hope they don't hit anything.

Others cut enough holes in the drywall (and/or floor, if carpeted) to see what they are doing. If using a camera system, those can be pretty small holes.

Drywall repair is a heck of a lot cheaper than plumbing and electrical repair.

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