How close can holes through joists be?
How close to each other can I drill holes in the joists in a ceiling to run 12/3 wire? I know the hole has to be 1 1/4 inch from the joist edge and can’t be more than 1/3 joist depth. I’m using 5/8 or 3/4 inch holes for the 12/3 wire. I don’t want to run too many wires through the same or larger hole so I don’t have to de-rate the current capacity of the wire.
I have a 100 amp subpanel that I am going to run 15 circuits around my basement workshop from. Even with using 12/3 wire to run two circuits (sharing neutral), it will get crowded in the small area around the subpanel where I have to route all the wires to the circuits to. I don’t want to compromise the first floor joists by drilling too many holes too close together. I also don’t want to have the inspector require that I replace all the joists either!
I want to run the wire though the holes so I can one day put up a removable Ceiling-Max acoustic ceiling. Drilling holes is also easier than running 1x2s to support all the 12 gauge wire. Thanks in advance for your help.
Replies
You don't have to worry about derating for holes thru joists. There is a new, stupid, exception in the '05 Code if you caulk the hole with fire-proofing.
Maybe drill 1" holes two or three inches apart and run three cables thru each one. [But don't quote me.]
~Peter
15 circuits for a basement shop? That's a lot of circuits.
My detached garage/shop has 10 circuits in a 100 amp panel and I'm running all sorts of machinery and lighting...including two, 220 legs (tablesaw and bandsaw). And this includes seperate circuits for my furnace and power roof venting; which your regular home panel should already be supplying..... seeing how your shop is a basement shop.
I've never tripped a breaker. Unless you plan on running a bunch of machinery all at the same time, you should double-check your electric supply needs.
Instead of drilling lots of holes through your ceiling joists, you could attach your romex cables to the underside of the joists and box this area in to resemble a soffit, or wiring chase. Construct the bottom panel of the soffit in a manner so that it can be easily removed...so if you needed to change or upgrade your cables in the future, you could easily do so. You could still install your desired ceiling material...just have it abutt to the soffit.
The soffit would not take up much horizontal space underneath the joists..approx 14-1/2 inches...allowing 15 cables side by side with a 1/4 inch gap in between, plus a 2X2 running parrellel on each outer end of the cable run. Attach a false bottom to the 2X2s and there you have a simple soffit that will take up very little headroom space in your basement. You could attach J channel to the 2X2s and install drop -in ceiling panels for your bottom soffit panel...instead of making this panel out of wood and having to paint it.
Just a thought.
Good luck.
Davo
Davo,A good idea that I may think about. Seems like no one is really sure what you can drill in a floor joist. I'm running individual ciruits so that I don't have to worry about sharing one circuit with two machines (table saw, jointer, planner, dust collector, band saw, miter saw, grinder, drill press, 1 for work bench front, 2 for work bench side, 2 for work bench back, air cleaner). yeah, it is overkill but when I reach 80, I am not going to have to worry about the wife and I popping breakers.Thanks for the idea,
DJ
Here is the code on drilling and notching. So mention of how close they can be. I would guess that you might want 2 diameter spacing between them.http://www.codecheck.com/pg03_04building.html#fb8notching"I'm running individual ciruits so that I don't have to worry about sharing one circuit with two machines (table saw, jointer, planner, dust collector, band saw, miter saw, grinder, drill press, 1 for work bench front, 2 for work bench side, 2 for work bench back, air cleaner). yeah, it is overkill but when I reach 80, I am not going to have to worry about the wife and I popping breakers."You definitly want the dust collector, air cleaner, lights, and any HVAC on separate circuits.But you really don't need all of those.If you leave the bandsaw on while running the miter saw them you shouldn't be in there.But if you wife and you both work at the same time then you can use more.But I would still look at the number.BTW, if you run them under the joist an other opiton is to use Stackers. That is a 3M brand, but there are others. They are a standoff clip for holding romex that will take about 3-6 in each. I don't know the height offhand, but you might need to run a 2x4 in stead of 2x2 parallel to them.
DJ
what type floor joists? Are they a manufactured product?
http://www.quittintime.com
Mark,
Joists are 2x12's 50 years old. Drilling through the new studs I put in to section off the basement for my workshop was easy. These Joists are HARD! Guess they don't grow wood like they use to.
DJ
Your overthinking it.
NM, Romex, is used under the 60C rating even though the actual insulation is required to be 90C rated. This is in effect a derating that takes into account the way that NM is typically run. Enclosed in insulation filled walls, run through tight spots and bored holes.
The limiting factor in how many cables you should stuff into a bored hole is not the ability of the wires to get rid of heat, the underlying reason for derating, but rather your ability to run cables through the hole in a timely manner. Long before you need be concerned about derating going through even doubled joists your going to have trouble physically pulling the cables.
When you can't pull the cable through the hole with one hand you need to drill another hole. Simple as that. Derating doesn't apply much in this situation. The confined area is usually only 1-1/2" or 3". When it gets to the point your drilling through 6" of solid wood you might want to use some care. I will say that once the cables make it through the stud it is best to spread them a bit. A little slack is good.
You can also drill bigger holes as long as they don't compromise the joist. I have often used 7/8", kind of have a favorite auger. If its just one or two cables 5/8" or 3/4" work well and drill quickly with a sharp bit. Smaller holes are faster to drill, easier on the drill and help, and 'center', maintain space to the edge, a little faster.
The one point I would change in your plan is the sharing of the neutral. Better to pull in two 12/2s unless it is a dedicated 120/240v circuit. Actual cost of wire is the about the same. Two wire cable, because it is linear laid versus spiral lay on the three wire, also pulls and strips faster.
Eliminating the shared neutral also eliminates a source of potentially serious problems and greatly simplifies troubleshooting if repairs are necessary. Lose that connection, through human error or simple wear and tear, and your voltage on portions of the circuit can fluctuate wildly. It can cause transformers, florescent ballasts and impedance protected motors to overheat. Worse case resulting in a fire.
Shared neutrals are not necessary or beneficial in residential construction. They increase risk while saving nothing. They make sense in commercial construction and three-phase systems but they don't make sense for single-family homes.
4Lorn1,
I do see your point about the shared neutrals. All the circuits in the workshop will be home runs to the sub-panel. I was thinking about using 12/3 to run some added circuits around the house to divide up the load on the original circuits (originally had about 6 120v circuits in the house total from what I can see). I may still use 12/3 to get the wire from the basement to the attic because of lack of pull room, but looking at what may happen if I have a loose neutral connection may change my mind.
Thanks for your wisdom,
DJ
Eliminating the shared neutral also eliminates a source of potentially serious problems and greatly simplifies troubleshooting if repairs are necessary. Lose that connection, through human error or simple wear and tear, and your voltage on portions of the circuit can fluctuate wildly. It can cause transformers, florescent ballasts and impedance protected motors to overheat. Worse case resulting in a fire.
I'm glad you posted that. I was going to run 12/3 for my kitchen small appliance circuits, but your post made alot of sense. If the neutral got disconnected between the kitchen & the panel, you could end up with basically one 240V circuit instead of 2 120's
To address your original question, section R502.8.1 of the 2000 IRC says the holes must be at least 2" apart, and at least 2" from top and bottom of joist.