MC cable support, unistrut.

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noxx

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I'm having a problem maintaining a lighting system in which the fixtures are fed with 12/4 MC cable, which is secured to strut using 1/2" EMT straps. The cable has become damaged at several points of support, and it's obvious to me that the use of a 3/8" "screw down" single piece type unistrut type would have prevented this. The original installer however, maintains that his installation is in compliance with 330.30.

Of course I insist that it's not, since the cable is damaged, it's obvious that the supports were not "designed and installed so as not to damage the cable".

Any suggestions for other resources on this? Opinions, etc?

Much obliged.
 
There's a few things I can do to correct the issue, including ty wraps, tho I consider them cheesy as all hell. What I'm looking for atm is some other way to clarify that the original installer was remiss in his strapping so that the needed repairs can be paid for. Despite having plenty to spend, our company is notoriously tight with their maintenance budget.
 
noxx said:
I'm having a problem maintaining a lighting system in which the fixtures are fed with 12/4 MC cable, which is secured to strut using 1/2" EMT straps. The cable has become damaged at several points of support, and it's obvious to me that the use of a 3/8" "screw down" single piece type unistrut type would have prevented this. The original installer however, maintains that his installation is in compliance with 330.30.

Of course I insist that it's not, since the cable is damaged, it's obvious that the supports were not "designed and installed so as not to damage the cable".

Any suggestions for other resources on this? Opinions, etc?

Much obliged.
Click to expand...
How do you use emt straps on stut ?
 
I'm taking a wild quess and assuming the fixture is suspended. Therefore it is able to move while being serviced or from some other force of nature.

MC is flexible, but is not designed to be bent beyond it's suggested radius and certainly not multiple times. So it sorta falls apart. Especially on pendant hung fluorecents and high bays that are subject to wind.

The fix is to rejigger the way the flex is supported to allow for movement in a more comfortable way for the MC, or use a different wiring method or material that satisfies your specific classification.(Tywraps are one way) (SO cord is sometimes allowable in short lengths.)

Or tell the guy who changes the bulbs to refrain from moving the fixture.:)

If the fixture is not moving, then someone or something is breaking the MC.
 
Sorry for not being more specific, I'll try to give you a better idea what's going on.

Essentially I have a large steel structure, subject to vibration, with an adjoining catwalk. Along the catwalk rail there are rigidly mounted fixtures chained together with MC cable. The clamp the original contractor used to install these is the common 1/2" strut EMT clamp (this whole mess should have been in pipe, really), like so

clamp1.JPG


Because the cable is not 1/2", but 3/8", the "pinch" of this type of clamp tends to distort the armor into an oval, which when subject to vibration leads to the seperation of the armor at support points. It seems to me that the use of the proper cable type clamp..

clamp2.jpg


Would have prevented or lessened the problem.

Of course the whole thing is an engineering honk-up, and MC should never have been allowed in this particular application. I'm dealing with over 450 fixtures, and I'm getting armor seperations all over creation.

Now you know, and I know, that the right answer is "Fix the d**n thing and sweat the blame later", however I work under a monolithic bureaucracy in which I can't turn a screw without eight forms signed in triplicate. So, what I'm essentially looking for atm is some re-inforcement that I can take upstairs and say "hey, this isn't the right support, now go play musical chairs with the blame game and get me an engineering change order to fix it".

I'm guessing that I'll have to fall back on "listed for such application" and get information from the manufacturer of the strap? The article on MC cable seems to leave it up for debate.

Coming from an industrial background, I can't believe anyone would use extended runs of MC cable in this environment, but that's another story entirely.

Anyway, thanks for the input, sorry I wasn't more specific in the original post.
 
Thanks for the clarification!

Very well done, I might add...

I cannot think of any code violations on this, and believe it to be one of those things that just did not work well and it falls under workmanship.

Depending of the time span between the installation and your complaint, you might have something to use to encourage the contractor to negociate a fix. You have nothing to lose by trying.

Special methods are used for special occupancies, like the explosion proof requirement and things like that, but if the customer does not specify a certain requirement when there is no special code requirement, the normal and legal support rules are all that need to be followed. It looks like he did that, but his idea just did not pan out well for you. I don't think you will have any help from the code, as you explained it to me, so what you have is a workmanship issue and a failed code legal idea.

The first and logical fix that comes to mind is the removal of the existing strut clap and the installation of a sleeve to protect the MC from damage due to the clamp. Loosening the clamp will not work due to the screws and eventually the clamp pieces falling on someones head...:)

I'm thinking a small piece of liquid tight plastic conduit cut and then split as a sock around the support point, which would secure the MC and also protect it from being pinched as a vibration cuff.

The vibration is what is causing the contractors idea to fail and it took time for that to materialize. I can't say for sure, but I may have made the same call in the same circumstances. It is a art, not a science sometimes.

Talk to him, or the powers that be, explain the issue clearly as you have with me, and perhaps, if the guy wants your business in the future he may come half way and fix this for you or with your help and guidance. I'm not too sure that the other clamp will do the trick. It might, or might not. You may need to form a anti vibration mount as I described or a saddle as we call it..
 
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Ty wraps might be cheesy in your opinion but they would be the cheapest easiest fix.They won`t distort the armor and are a quick install.Or use tie wire also cheesy but cheap/quick install.
 
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