MC Cables Runs

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mkgrady

Senior Member
Location
Massachusetts
I'm looking at a job that needs numerous dedicated circuits run from a panel board to HVAC units in a school. The route is through utility tunnels, above suspended ceilings and through some pipe chases. Some runs will go through cored holes in floors to get to the first and second floor from the basement.

Is there a limit to how many cables can be tie wrapped together and supported? Are tie wraps adequate support for MC cable? I imagine I will have to find some kind of "J" hook that is suitable. Most of the wall and ceiling surfaces are some type of concrete or brick.
 
What size MC cables? For #12 the exception is pretty liberal meaning that you can bundle up to 20 CCC's before you need to derate.
 
What were you planning on tie-rapping to? Caddy makes "J' hooks that work on walls, and ceiling wires. You could probably bundle as many together as needed depending on how you support them. I don't think Tie-raps are listed for MC cable support. There's always ladder rack (jk)
 
infinity said:
What size MC cables? For #12 the exception is pretty liberal meaning that you can bundle up to 20 CCC's before you need to derate.
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The MC is 12-2. I guess that would mean 10 of them before I have to derate. Considering most of the loads are 3-7 amps I could bundle even more than 20 CCC's.
 
mkgrady said:
The MC is 12-2. I guess that would mean 10 of them before I have to derate. Considering most of the loads are 3-7 amps I could bundle even more than 20 CCC's.
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Yes you could but then (after 20 CCC's) you would need to apply a 60% derating factor which might bring your #12 down to 15 amps or 20 amps if you have no multi-receptacle circuits using the next size up rule.
 
joebanana said:
What were you planning on tie-rapping to? Caddy makes "J' hooks that work on walls, and ceiling wires. You could probably bundle as many together as needed depending on how you support them. I don't think Tie-raps are listed for MC cable support. There's always ladder rack (jk)
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Ladder rack sounds like way too much work. I don't think I use the ceiling support wires though I wish I could.

I have wondered about the caddy mustache clips but I'm guessing they are for individual cables? Not even sure how they work. Attach wire to ceiling with it hanging down. Attach mustache clips around MC and attach to wire. What keeps the wire rigid if not connected to ceiling grid?

Most MC I have run has been over bar joists and through steel stud walls. This place has neither.
 
ActionDave said:
There is no allowance for the load with bundling rules and derating.
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True. There is a scenario where you still might need to use the load rating when applying the 60% derating with the next size up rule.


310.15(B)(5) An adjustment factor of 60 percent shall be appliedto Type AC cable or Type MC cable under the following
conditions:
a. The cables do not have an overall outer jacket.
b. The number of current carrying conductors exceeds 20.
c. The cables are stacked or bundled longer that
600 mm (24 in) without spacing being maintained.
Click to expand...
 
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