I need to pass a bipolar electrical cable through a concrete beam (30cm high, 15 cm wide) (12x6 inches). The hole would need to be about 1cm (3/8").

Is it safe to drill through it? There is no wall below it and one of its columns is "upside down" (see sketch below).

concrete beam with upside down colum

Edit: I did some further research and found some regulations regarding holes and openings on reinforced concrete beams. There is no need of additional reinforcement if the following is observed:

  • hole in the traction zone of the beam.
  • diameter limited to 12cm or 1/3 of beam height
  • distance from supports equal to 2 beam heights

So in my case I would have to have the hole around 60 cm from the column in the bottom portion of the beam, and the diameter is below the threshold (around 1-2 cm). Is that right??


2 Answers 2


As you (the OP) have discovered, small holes in concrete are perfectly acceptable.

No disrespect to other posters, but likening concrete to glass is inaccurate. Also, hitting chunks of igneous rock is never a problem in my experience. (Hitting rebar is a problem, though. You'll want to be careful when drilling... If you suddenly stop making progress and you've already cleared the dust, then pull back and either try to subtly change the angle or drill a different hole.)

  • I got worried because this is a load bearing beam, but it all indicates that the risk is negligible. I will be using a rotary hammer drill with SDS bits (probably predrilling with 6mm and enlarging to 10 mm later). Since I won't need the hole right now I will wait for further input regarding that. Mar 20, 2016 at 16:57

Run your wire around it or run it somewhere else. Concrete, even with rebar, is nothing like wood. Drilling through or even into the bottom half could release the tension & be major problems. Through the vertical legs, yes absolutely & no problem. But, in a long span, not a good idea at all.

  • The span is about 4 meter and this beam supports one edge of the slab on top of it. It will be really hard to go around it (the wire wasn't supposed to show). I will think more about it, but if this is really unsafe I will have to let the cable show. Mar 19, 2016 at 23:54
  • I edited my question with more information that I found out regards holes on reinforces concrete beam. Mar 20, 2016 at 0:43
  • 1
    I can see that it makes sense given the amount of material & the tiny size of the hole as well as its location. But, what's the stress on this beam? Does it already bounce when people walk around, it's a big unknown. What happens when you can't get your hole through that much material (that's more than most foundation walls) because of rebar or hitting granite, diorite or quartz chunk? I'm just saying go with Plan B & skip Plan A. We're talking about a wire, so get more wire or even a lot more wire. Can you give me any links? Just copy & paste them into comments.
    – Iggy
    Mar 20, 2016 at 3:13
  • The regularion is from the Brazilian standards association in portuguese (i guess is equivalent to ANSI or some other), it is regarding requisites for concrete structures: ABNT NBR 6118:2003. Mar 20, 2016 at 3:39
  • 1
    Sorry, I just don't think it's wise & there's always another way. how about Wiremold or Raceway tucked in the corner of the room? You won't even see it. Otherwise, I'd really have to say, get a local Engineer, with a Certificate Of Insurance that you confirm, to write up a report with recommendations & even testing of the concrete's constitution. Then you'll have someone to chip in if you decide to go ahead & bad things happen. If it was wood, then no problem. But, concrete is like glass & drilling INTO it is night & day from drilling THROUGH it.
    – Iggy
    Mar 20, 2016 at 3:51

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