What We Cover in this Article:
- How Many Holes Should you Drill for Wires?
- Different Drill Bit Sizes
HOW MANY HOLES SHOULD YOU DRILL FOR WIRES?
Pre-planning is what will separate you from others in terms of speed in residential wiring.
It’s important to do a walk-through of the building you’re wiring to form a quick game plan. (We do this by reading our prints.)
Think how many holes you’ll need in your top plates when coming down to your switches and plugs, and where they’ll be going after you pull the home run to each destination.
(Also plan how many holes you’ll need for your home runs, too).
If we look at a lighting circuit for example:
What other lights are powered off that home run?
You first have to count how many lights are going to be on the lighting circuit and then get an idea of how many wires you’ll need generally to that switch.
You’ll need a power in, a power out, and the switch leg to each light, except the last one, which should only have a power in and the switch leg.
I’ve learnt over the years to always bring power to my switch. This allows convenience and simple troubleshooting if problems arise. (You can open up a switch to find the home run, rather than having to take down lights and figure out the circuit.)
After doing a quick pre-plan, it’s now time to drill.
During your drilling process, if you miss any holes, this is what slows you down because now you have to go back and pick up the drill just for the sake of one or two holes you missed. (If someone took the drill, you have to go find it and all of this cuts into your time!)
So with that said, how many holes should you drill and how many wires can you fit in a hole?
From what I’ve experienced in my years, we typically use 1″, 7/8″, and 3/4″ auger bits as electricians in our homes when pulling our branch circuitry.
Depending on the size of drill bit you use, typically I’ve seen two to four 14/2’s in one hole.
14/2 and 12/2 NMD can be shared in the same hole. (12/2 would be for kitchen counter plugs or certain heating loads like baseboard heaters.)
10/2 or 10/3 NMD usually get its own hole. (Dryer or P-Tacs).
8/3 also gets its own hole (stoves/ovens/ranges, and sometimes furnaces/AC units.)
It’s easy to burn the insulation off of your wires if you’re pulling a wire through an existing hole with a wire. Never pull super hard and fast as that will burn the insulation. Pull slow and just keep an eye on the other wires as you pull.
This is kind of a, “If it doesn’t feel right, just drill a new hole”, approach.
Another thing to mention is your power cables cannot share the same holes as low voltage cables such as telephone, data, or coax. You must be at least one foot away to prevent induced EMF to these low voltage wires!
DIFFERENT DRILL BIT SIZES
As mentioned, I’ve mostly seen drill bit sizes from 1″ to 1/2″ when drilling out a home or condo unit.
Typically we use augers because they are fast and can even drill through nails; it’s best to avoid hitting nails to improve the life of your auger bit, though.
Sometimes, I even like to use spade bits in my hand held drill as I find they drill extremely easy, especially in a tight situation where you could possibly drill through something on the other side.
The only times we start to use bigger drill bits is for our panel feeders, a big hole above the panel for all our wires to come down, or if we’re drilling holes in the hallways of condos so we don’t have to drill tons of holes; just one bigger sized hole for multiple wires.
On these big holes, the type of drill bit changes though. Instead of an auger, we may use a forstner bit. (Try your best to avoid nails with these bits! They are awesome to use, but can easily be damaged by nails!)
CONCLUSION – HOW MANY HOLES PER WIRE
Residential is different than commercial in terms of how many wires you can fit in a hole vs. how many wires you can fit in a pipe. (See an electrician’s guide to roughing in).
Our Canadian Electrical Code Book has specifications for how many conductors we can pull in a pipe, but I don’t believe there is one for how many wires through a hole as a residential electrician.
With that said, you have to think about the theory of why the code restricts how many wires can be in a conduit.
It’s simply because of heat. (In commercial, this is also so you can add an extra circuit at a later date because the pipe isn’t jam-packed.)
I’d say two-to-three 14/2 NMD wires is a good number per hole in a wood stud. It’s not hard to just drill another hole to have peace of mind from bundling up all your wires and adding to the heat.
Just remember to drill your holes level, and be careful to check on both sides of the stud before drilling, and understand what you’re allowed to drill through in a wood framed electrical environment! 🙂
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