Running wire through floor joists.

Reply

  #1  
Old 11-08-06, 11:10 AM
JoeTheZombie's Avatar
Member
Thread Starter
Join Date: Nov 2005
Location: Idaho
Posts: 216
Received 0 Votes on 0 Posts
Running wire through floor joists.

Although not technically an electrical question, it does pertain to electrical installation more than any other forum, so I will go ahead and post this here.

I remember reading somewhere concerning rules about drilling though floor joists, but I can't find it anymore. What rules should I follow when drilling through joists? I try to drill my holes pretty much center of the joist height, but I thought I read somewhere about no holes in the center third of the joist length.
 
Sponsored Links
  #2  
Old 11-08-06, 12:45 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Vertically, holes should always be inside the middle 1/3 of the joist, and hole diameter should never exceed 1/3 of the actual (not lumber dimensional) height of the joist.

Horizontally, holes may be anywhere along the joist except within 2" of the supported ends. Notching is not allowed in the middle third of the span, but holes are.
 
  #3  
Old 11-08-06, 08:10 PM
Banned. Rule And/Or Policy Violation
Join Date: Feb 2006
Location: North of Boston, MA.
Posts: 2,113
Received 0 Votes on 0 Posts
What is the application-location of the wire install?
In a certain applicatio/location, You may not have to drill at all.
 
  #4  
Old 11-08-06, 08:33 PM
Member
Join Date: Mar 2005
Location: Chesapeake, VA
Posts: 340
Received 0 Votes on 0 Posts
Code places specific restrictions on where you can drill/notch. Generally speaking, the smaller the hole, the better. And the closer to the center of the joist, the better. Beams stiffen as the cube of the thickness of the beam- cutting a hole twice as big weakens it 8x! But when the hole is in the center and relatively small (1/2" or so), the amount it weakens the joist or beam is completely insignificant- less than 1% of the strength. Center-boring a 1/3 hole weakens it by only a surprising 4%.

When the hole is drilled near the edge, it has a very significant impact- drilling a 1/2" hole in the center weakens a 2x4 by .3%, but drilling that same 1/2" hole near the edge weakens it by almost 40%!

When a joist is directly over a load-bearing wall, this equation changes, as the joist is acting like a very short stud, and any hole weakens it directly proportinate to the size, plus stress concentration factors- drilling a hole 1/3 the size of the stud weakens it by about half.
 
  #5  
Old 11-09-06, 05:16 AM
Member
Join Date: Feb 2006
Location: USA
Posts: 6,606
Received 7 Votes on 7 Posts
Drilling joists

You are correct on the lengthwise limit. Do not drill in the center 1/3 of the length of the joist.
 
  #6  
Old 11-09-06, 12:10 PM
Member
Join Date: Jan 2003
Posts: 111
Received 0 Votes on 0 Posts
Local codes may vary, but typically, for dimensional lumber:

As Ben said, for boring or drilling the hole must be at least 2 inches from the top or bottom edge of the joist. The diameter of the hole cannot be more than 1/3 of the joist depth. The hole can be anywhere along the joist’s span, or length.

It is notches that cannot be in the middle 1/3 of the joist’s span.

For engineered joists:

Always follow the manufacturer’s specifications.
Do not notch or bore the top or bottom chords.
Typically, most have perforated knockouts and holes smaller than 1 ˝ inches in diameter can be placed anywhere along the span. Larger holes should be placed closer to the center of the span.
 
  #7  
Old 11-09-06, 07:05 PM
Gen
Gen is offline
Member
Join Date: Jun 2006
Location: US
Posts: 420
Received 0 Votes on 0 Posts
One more thing--holes must be at least 2" apart from each other.
 
  #8  
Old 09-27-08, 06:49 AM
Member
Join Date: Aug 2008
Location: Chicago Suburb
Posts: 15
Received 0 Votes on 0 Posts
These posts were helpful but I have a few specific questions.

I am looking to run 12 NM Romex cables from a subpanel in my basement workroom to the finished areas of my basement. To do this I need to run the cables through nine 1.5"x11" floor joists that are 16 ft. long. The cable run would be about 12 ft.

Currently I have one 1.5" hole drilled in the middle of the 16 foot long joists. The holes are drilled about 4-5" from the bottom of the joist.

Can I safely drill 2 more 1.5" holes in the joists to run the cable? I assume the holes need to be no closer than 2" apart and 4-5" from the bottom of the joist.

Thanks!
 
  #9  
Old 09-27-08, 07:57 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 15,001
Received 40 Votes on 35 Posts
Are your joist dimensional lumber like a 2x10 or are they engineered joists?
 
  #10  
Old 09-27-08, 10:06 AM
Member
Join Date: Aug 2008
Location: Chicago Suburb
Posts: 15
Received 0 Votes on 0 Posts
They are not engineered. They are 2 x 12's, or 1.5 x 11.25.
 
  #11  
Old 09-27-08, 12:13 PM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
How many cable you are plan to bring in ??

Normally with 1 inch hole you can bring in many as 3 or 4 12-2W/G without much issue I know you can stuff more but from my past experince 4 is about the top you can pull in techiallywise yeah you can get more wire in there but not a wise idea anyway.

Just make sure you have stright shot holes so the wires can slip in very easy and a nice tip along the way unravail { uncoil } the wire first to make it nice and straight so it will really go in very fast without any kink or something can get ya by suprised.

Normally with dimison standard lumbers you should not have any issuse with the boring the holes as it was descrbing above this comment.

Merci,Marc
 
  #12  
Old 09-27-08, 02:06 PM
Member
Join Date: Aug 2008
Location: Chicago Suburb
Posts: 15
Received 0 Votes on 0 Posts
Yes, as you stated, my plan is to run 3-4 cables (12 and 14's) per hole, but I thought I needed a 1.5" hole to do this. Are you saying a 1" will do the trick?

If so, can I assume it's not a problem drilling the holes 2-3" to the left and right of the existing 1.5" hole and at the same hieght. Does it matter?
 
  #13  
Old 09-27-08, 07:39 PM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
I been boring holes in resdentiail and commercal/Industrail and done right it will have no issue with it.

The situation you have there you will have no issue with that set up.

Yes you can bore a hole on common lumber either side as long you are not close to the end of the board itself and the lumber itself is good shape no knowen cracks or weak spots at all.

Merci,Marc
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: