Routing Cables Through Open Framing

Pre-wiring a job site for low voltage differs from 110/220 electrical from the aspect that we cannot interfere with their system, but they can interfere or affect ours. It is most common for all other trades to have their wiring, plumbing, and HVAC mostly completed before the low volt installer walks on to the job site. This has benefits and negatives for the low volt installer.

The benefits are you can see what goes where and layout your paths to avoid power or being in the way for other trades. The HVAC installer does not care how much inconvenience it is for you to mover your wire because their duct MUST go through a bay where you have wires. You will be the one to move. The electrician has no concern when they route a 220VAC  wire parallel to your camera wires for 20 feet.

The negatives are,  there is often no easy path(s) left for your wires. You have to get creative and be cautious when drilling. The best time to start your pre-wire is when the electricians are about 1/2 way into their job. They have their paths established, and usually, the other trades are done. 

Here is the typical order that trades are on a job site for open framing work.

Plumbing for Water / Sewer / Sprinkler
HVAC
Electricians
Low-Volt 
Insulation

This order is generally the preferred order to keep trades from being in each other's way, but there are times you will find multiple trades in the middle of the work at the same time. If you find your self on a job site where there are several trades routing their materials through open framing at the same time, be nice!  If you see your path might be in someone else's path, ask them. It is easier to move your path before you have your wires secured. Working with other trades will save you time in the long run. 

 If you are starting your wiring before other trades are finished, you need to be aware of spaces and paths that may be needed for them. If you see a bunch of empty holes, do not assume you can run your wires through them. It is very common for electricians, plumbers, and HVAC to pre-drill an entire site days before they start pulling wire or installing pipes and ductwork. Take the time to think about what you are doing and how it may affect someone else.

Horizontal Drilling Paths

Horizontal paths through walls can be the most time consuming due to the amount of drilling.  Sometimes you have no choice and will need to drill paths through multiple bays.  The graphic below shows the areas to avoid. The top and bottom ends of studs are bad to drill through because it affects the integrity of the stud. Within a few inches of the end, you also increase the risk of hitting nails. 
The light switch zone is too busy with wires and electrical boxes. The outlet zone is also busy and lower will be to close the end of the stud. 

Showing horizontal paths in open framing

     Hole Size

When you do drill through framing, selecting the proper hole size should not be overlooked. In a standard 2x4 wall should try to use a drill bit 7/8" or less in diameter. NEC requires that if you have less than 1-1/4" from the edge of the hole to the face of the framing, or sheathing (if installed), you must install nail plates (NFPA 72 300.4). Since a 1" hole is the maximum size hole, you could drill before forced to nail plate, a 7/8" hole allows for wiggle room in how close you drill to center. Be careful when drilling so that you do not drill at such an angle that the hole starts out in the middle but comes out too close the edge. 

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CAUTION:

Be very careful to not drill through beams, support columns, or load-bearing walls without first getting permission from the site contractor. ASK BEFORE YOU DRILL.  More information on drilling beams. 

 

Vertical Drilling

The drawing below shows the locations to avoid when drilling up or down within a wall. Always check the backside of the area you are drilling. Avoid drilling into other support structures such as doubled-up joists, rafters, or steel brackets. Before you start drilling, look around to see if other trades are finished. HVAC, plumbing, and gas are the most common trades that will require you to relocate if you are in bays they MUST use. It is always advisable to ask the site general contractor if all other trades are complete and if not, will your pathways be OK.   

 

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Clearances from Electric Light and Power

Essentially, unless the electrical wiring is Tube and Knob, there is no clearance required between low voltage and electric light or power wiring in open framing.   (NFPA 72-2017,  760.136(G)(1) for Fire Wiring and 725.136(D)(1) for other class 2,3 conductors). If the power wires are metal-clad or in metal conduit, separation is not an issue.

When the power cables are non-metallic sheathed, there are required clearances in other standards for communication and data systems. TIA standards vary depending on the size and current in the power cables and are too complex to cover here. The general rule of thumb is to maintain at least 6" separation in parallel runs with typical wiring found in residential and small commercial applications. Further separation is never a bad goal, and if you can keep several feet away, all the better. 

The drawing below shows a typical wall and wiring. Notice the secure locations of the wires. Cables should be routed at right angles and never routed diagonally through a wall cavity. When insulation is installed, the installers need to cut and(or) separate the insulation bats to place insulation on both sides of your cable. Cables routed diagonally makes it difficult for the insulation installers and does not look neat.

 

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