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Our home in Toronto was built in the early 70s with aluminum wiring. Since we are doing a bunch of renovations we took the decision.to replace the existing aluminum wiring with copper wiring.

The electrician has created multiple holes in the wall studs to run the new wiring (pls see attached pics). According to him as per code he can only run a single cable through each hole. The studs look a bit like Swiss cheese and we wanted to get the opinion of the forum experts. EDIT: Please note this is an exterior wall

Is he right? Is there not a better way of running the wires? Should wires be protected by metal plates across the studs to prevent damage from screws/nails? Any other things we should be aware of or pointers you can share...

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  • You can actually request an inspection here – Nelson Oct 10 at 5:21
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    Classic exterior gyprock sheathing... don't see much of that anymore! Presumably there will be insulation going into this wall and the biggest issue there might be to get the batts installed in such a way that all of that cable mess doesn't completely compromise the insulation value. Keep an eye on your contractors when they get to that step. Might consider using loose fill, at least for these section. – J... Oct 10 at 15:14
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    Actually electric inspections are done through ESA. Electrical safety authority. Get them to provide proof of the electrical inspection as passed. Must be inspected or insurance probably will not cover claims. Aside from that, looks like good work. The no holes in the middle third applys to joists. Holes are centre of the stud and the spacing between holes is 1 1/2" between centre or greater. – user68386 Oct 10 at 23:15
  • I'm not from North America, so a quick sub-question: Isn't an external wall based on this kind of array of studs rather flimsy? Just looking at that thing makes me afraid the house will collapse on my head. (In my country it's either concrete or stone, and no less than 20cm or 25cm thick.) – einpoklum Oct 11 at 7:47
  • @einpoklum -- it depends on what you're up against. Wood's strength comes from its flexibility, really... – ThreePhaseEel Oct 11 at 11:38
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You can divide this problem into 2 aspects: First, protecting the lumber integrity when running wires. Second, protecting the electrical wires from damage.

For load bearing studs (there are less stringent standards for non-load bearing), here are the key (U.S. - you can extrapolate for Canada) requirements for 2x4 studs under 10 feet in length:

LUMBER INTEGRITY

  1. No holes or notches in the middle 1/3 of the stud.
  2. Never put a hole and a notch at the same height.
  3. Multiple holes (except 2 side-by-side holes only) must be drilled in the centerline of the stud.
  4. Side-by-side holes require steel plates on both faces.
  5. Holes should not be bigger than 40% of the stud width (max 1 3/8").
  6. Notches should not be bigger than 25% of the stud width (max 7/8").

WIRE PROTECTION

  1. Steel plates should be at least 1/16" thick; plates should be notched flush with the stud edge.
  2. All notches require steel plates.
  3. Holes closer than 1 1/4" to the finish surface of the stud require steel plates.

OTHER COMMENTS

  1. A "better way of running the wires" is to use either armored cable or conduit. Either of these will dramatically increase the cost of this install.
  2. Your electrician is correct in running only one cable through each hole to avoid damaging the insulation with heat (otherwise they must be derated (reduces the current flowing through them), which is impractical).
  3. Holes for the same cable should be at the same level, to reduce wire length and protect the insulation when pulling the wire.
  4. Everyone should replace their aluminium cable and connectors, which cause many structure fires around the world, kudos to you.

REF: Journal of Light Construction

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    holes closer than 1 1/4" to the finished surface of the stud - this is wrong. I've seen this printed sometimes, it is 1 1/4" to the finished surface of the wall ( the same length as standard drywall screws ). Lumber integrity - no holes in the middle 1/3 of the stud that's ludicrous. Where is your JLC reference link? No one notches the studs for the steel plates, you'd have people knotch a 1/16" recess into studs to accommodate a nail plate? Walls/studs are rarely within 1/4" plumb tolerances across their height/length, 1/16" - that's for metal parts in machinery. – Fresh Codemonger Oct 10 at 17:26
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    This is the western wood products association guide to notching and boring. You'll need to create a free account but the PDF is my go to for the notching boring requirements in studs/joists and I post it at my building sites for the trades. wwpa.org/docs/default-source/secure/… – Fresh Codemonger Oct 10 at 17:34
  • JLC Field Guide to Residential Construction - A Manual of BEST Practice; Volume 1 - Notching and Boring Studs and Plates p 134. And, Volume 2 - Drilling and Notching p 33 & 35.....You can easily notch a 1/16" plate in a stud with a special tool called a router. Please give me the reference to your "ludicrous" statement. – jack c Oct 11 at 3:25
  • The ludicrous portion was your lumber integrity #1 - the only thing I see in the field guide that resembles that is not notching or boring the middle third of a joist. Rough framers don't carry routers, electricians are not carrying routers, no one is routering for rough in of electrical. Having a nail plate proud of the surface of framing lumber is well within tolerances of rough framing and just has little to no effect on the drywall. – Fresh Codemonger Oct 11 at 8:14
  • Appreciate all the responses and jack c while we felt replacing the aluminum wiring was the right thing it is an expensive choice. – user105375 Oct 11 at 11:23
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Looks like a standard install.

You can only run so many wires in a hole without de-rating the circuit capacity.

The holes are set back at least 3/4" from the stud surface, add 1/2" for drywall and you get 1 1/4" the length of the drywall screws. Even if the drywall screw goes into the same line as the hole it isn't long enough to penetrate the wire. If the holes were closer than 3/4" from the surface then they need metal plates.

There are guidelines for drilling studs/joists in non bearing/bearing walls/assemblies. Typically you don't worry about the electrician as their holes are too small and if you do worry you worry about the joists not the studs.

https://www.familyhandyman.com/walls/drilling-holes-notching-and-boring-holes-in-wood-studs/

  • Well stated. Covered all the relevant points. +1 – Harper Oct 10 at 7:41
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    @J... They often fail by bending (eg wind etc) before compression is a real issue. – Walker Oct 10 at 14:44
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    The metal plates are cheap & easy to install, personally I would just do them and reduce the risk of damage. Other things than drywall screws are likely to be used sooner or later. – DaveInCaz Oct 10 at 15:04
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    @Walker I think thats the exact point being made, using that extra land to reduce fire risk and thick walls for insulation is a waste one cannot afford in places where the land itself is extremely valuable compared to the work and materials. – Vality Oct 10 at 17:08
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    @FreshCodemonger you were not exporting them at the time of the Fire of London. – Walker Oct 10 at 17:21

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