300.4[e]

[iwire]

So Bob, by your interpretation you cannot run EMT on the underside of the metal pan unless it were mounted on 1.5" or larger strut?

Yes that is exactly my view. :smile:

Is the section aimed at protecting raceways and cables from screws?

Do screws typically come through the lowest rib of the metal pan?

My thought is that it's to prevent it from being run between the top of the bar joist and the metal pan unless you can maintain a 1.5" space.

I wish that was so but I do not believe it to be.

 

[sparkyboys]

you could drill 3/8" holes, then use 3/8 lead anchors with all-thread and conduit hangers, thats if you do not want to run a rack and if its only a single pipe. will need nuts, lock washers, and washers

 

[infinity]

Yes that is exactly my view. :smile:

Is the section aimed at protecting raceways and cables from screws?

Do screws typically come through the lowest rib of the metal pan?

I wish that was so but I do not believe it to be.

The IAEI agrees. For guys who do this type of work this change is tremendously more labor intensive/expensive than the old method of just screwing to the underside of the metal pan. I understand the concern here but IMO this change goes too far.

300.4(E).
Analysis of Change:​

Roof decking is often repaired or replaced after the initial installation and there has been a
history of penetration by screws and other mechanical devices that hold the decking down.
Cables and raceways which are supported by the roof deck must have supports (such as​

hangars or strut) that provide a 11⁄2" space from the deck to the cable or raceway.

Copyright IAEI ​

​

​

​

? 2007​

 

[iwire]

For guys who do this type of work this change is tremendously more labor intensive/expensive than the old method of just screwing to the underside of the metal pan.

You bet, even where we were not screwing to the pan we always ran above the truss / beam in the ribs with MC or pipe.

 

[elohr46]

I know the 08 restricts conduit within 1 1/2" of the "nearest surface of the roof deck" to protect raceways from the deck screws.
We are doing a job that will have 4" of concrete between the roof material and the deck.
Any opinions?

I would say that if your roof deck is 4' of concrete your are good to go, no deck screws should be used in that type of constuction. I would still check with the AHJ first.

 

[iwire]

The only way to know for sure is to consult with the AHJ...

On the positive side, what you describe may not be metal roof deck. The construction is actually a composite metal deck, or a composite concrete slab with steel decking,

I see it the same way, it is not a metal deck it is a concrete roof deck but the only opinion that really matters is the AHJ.

 

[dcspector]

I see it the same way, it is not a metal deck it is a concrete roof deck but the only opinion that really matters is the AHJ.

Agreed same here Bob. Now on a concrete deck if they forget to xray before a future roof deck core thats their problem. Just an example.

 

[benaround]

Has anyone actually had a roof screw go thru an emt or mc cable ?

 

[dcspector]

Has anyone actually had a roof screw go thru an emt or mc cable ?

Must have or otherwise it would not be in the NEC....:grin: Kiddin of course.

 

[Bryan Price]

Has anyone actually had a roof screw go thru an emt or mc cable ?

Many times yes. So I do understand 300.4 intent. But it does leave it a little unclear.

I do want to thank you all for your responces.

 

[benaround]

Using the same logic, I wonder what code could be made for underground pipes ? Around

here they get hit on just about every job.

 

[electricmanscott]

using the same logic, i wonder what code could be made for underground pipes ? Around

here they get hit on just about every job.

300.5 :-?

 

[JohnJ0906]

Has anyone actually had a roof screw go thru an emt or mc cable ?

The screw didn't penetrate, mostly due to the EMT flexing.