Do I need to run wires through holes in trusses?

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  #1  
Old 10-29-06, 08:21 AM
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Do I need to run wires through holes in trusses?

I am adding electrical to a detached garage. It was built using pole barn construction. The roof has trusses 48 inches on center ( The trusses are pre-manufactures and made of 2x4s). On top of the trusses are 2x4s (laid flat) running perpendicular to the trusses - 24 inches on center. On top of the 2x4s is metal roofing. I would like to run wiring parallel to the 2x4s (perpendicular to the trusses). Do I have to drill hole throu the trusses when I cross them. I am using MC cable. Can I go over the trusses and put clamp on each side. If I do have to drill holes, is there any significant effect on truss strength?
 
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Old 10-29-06, 09:07 AM
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DO NOT drill 2x4 trusses!!

Run the cables on top of the trusses, along the strongbacks. Staple the cables at each truss.
 
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Old 10-29-06, 09:11 AM
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1)Will there be a finished ceiling on the inside when complete? 2)Will it be strapped off first?
I see no problem running on top of the truss.
1-2 If yes, I would rather go below the truss,more protection.
Either way It must be secured.

also, you can't wire untill the building is weather tight. IE; roof ,windows. Here some require the tyvec on too.
 
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Old 10-29-06, 09:25 AM
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I don't want to go over the top member of the truss. The MC cable is 7/16 thick, the space between the top of the truss and the roof is 1 1/2 ( 2x4 on its side) - minimum space per the NEC is 1 1/4. I want to go under the top member of the truss. Since MC cable can't be bent sharply (minimum bend radius of 7x the cable diameter), I was going to go under the top truss member and put a MC strap on each side of the 2x4 that runs perpendicular.

I don't intend to finish the ceiling on the inside. I run the wires as high up as possible so that I can hang stuff on the lower members of the trusses ( I specified stronger lower truss members for this purpose
 
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Old 10-29-06, 09:31 AM
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I was talking about on top of the lower truss members, not between the roof.

In this case just staple the cables on the underside of the upper truss members as you intend.
 
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Old 10-29-06, 09:43 AM
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on top of the lower truss members, not between the roof.

Likewise.
 
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Old 02-28-07, 12:58 PM
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hang stuff on the lower members? make sure that it isnt heavy load or make sure the trusses are engineered to take the load, prefeab trusses walk a very thin like and have to be checked for every detail.
 
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Old 03-01-07, 08:28 AM
jn
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Never ever drill through trusses.
I would run the wire along the bottom (opposite side of metal roof) of the 2X4's that run perpendicular to the trusses. Pick a board that runs close to the corner webbing of the truss if possible. That way the wire is in a protected underside corner where nothing could hang on top of it as it crosses the truss. Cross the truss on the lower side (not between the metal and truss but through the truss) and clamp it in the protected corner area of the truss. Clamp it to keep it from sliding into the sometimes sharp metal that sticks past the edge of the truss web.

I dont think you could run across the top of the lower truss member, as has been said, because it does not sound like you have the 2X4's running perpendicular to trusses there (remembering pole barn contruction). There would be nothing to support the wire between the widely spaced trusses. That is why I prefer the above method....
 
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Old 03-04-07, 10:33 AM
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Your trusses should be tied together (the length of the building) with lateral bracing on top of the bottom chord, 2x4's in your case. How many runs depends on width of bulding. you could attach wiring to side of this lateral bracing. Or could run a 1x4,or 2x4 for that purpose. Like Speedy Petey wrote, Do Not Drill Holes In Trusses.
 
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Old 03-05-07, 11:41 AM
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Quote from RJA1: "Your trusses should be tied together (the length of the building) with lateral bracing on top of the bottom chord, 2x4's in your case. How many runs depends on width of bulding."

RJA1, This is not necessarily the case. I have seen and wired many pole barns that had absolutely no bracing in the design that tied the bottom of the trusses together. Some do, some don't. If it is there you could use it, if it is not there you could certainly add it. I am making this comment because I want the OP to be aware of this so as not to be alarmed if he is missing such lateral bracing.
 
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Old 03-05-07, 11:54 AM
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Don't worry much about the OP. He hasn't even visited this forum in the last five months.
 
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