How high conduit off roof? [RE-wrenches]

[Bill Brooks]

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Adding to Bob-O's post,

Severe physical abuse is generally in the vacinity of fork lifts, floor
sweepers, and other vehicles that could run into and break conduit. That is
why many industrial sites require rigid in these areas. A roof would rarely
be exposed to this type of traffic unless it was some kind of parking
structure. Severe physical damage can also be addressed by installing pylons
that prevent traffic from running into the conduit.

Distance off the roof has as much to do with protecting the roof as it does
the conduit. There are several manufactured products that raise the conduit
a variety of heights from 1" to 6" or more depending on the situation. The
closer conduit is mounted the roof, the more likely it will come in contact
with the roof and damage the roof. Also, there is also the tendency to trap
debrise with a smaller gap. I think a 2" height is sufficent for most
installations as long as the conduit is supported as directed in the code.

Bill.

-----Original Message-----
From: Bob-O Schultze, Electron Connection [mailto:econnect at snowcrest.net] 
Sent: Tuesday, August 30, 2005 7:53 AM
To: RE-wrenches at topica.com
Subject: Re: How high conduit off roof? [RE-wrenches]


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Gang,
I've looked through the 2005 NEC and can find no stipulations about EMT 
or any other conduit needing to be installed any distance from the 
roof. Certainly there are guides for the distances between supports, 
etc. Of course, the reason that AHJs have leeway to interpret the Code 
is that different regions have different climate conditions which may 
lend themselves to different best practices. Fair enough. I've never 
heard of anyone interpreting the Code to call a roof a place where 
conduit is exposed to "severe physical abuse". That seems pretty over 
the top and worth a challenge.
Cheers, Bob-O
On Aug 29, 2005, at 11:10 AM, Joel Davidson wrote:

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>
> Jeff,
> You're right about EMT not permitted where it will be subject to 
> severe physical abuse. NEC says securing supports within 3 feet of 
> tubing terminations, but I also put a block right at the couplings 
> because that's what comes apart when people trip over or step on the 
> conduit. Joel Davidson
>
> Original Message:
> -----------------
> From: Jeffery Wolfe, Global Resource Options
> jeff at globalresourceoptions.com
> Date: Thu, 25 Aug 2005 23:09:36 -0400
> To: RE-wrenches at topica.com
> Subject: RE: How high conduit off roof? [RE-wrenches]
>
> Joel,
>
> Code does stipulate (I do not have it in front of me, but I have seen 
> the reference) that EMT cannot be installed in areas "subject to 
> mechanical abuse". I have had inspectors claim that all conduit on the 
> roof falls under this, as it gets wind, snow and ice (around here), 
> trees falling on it, people tripping over it, etc.
>
> We check with the local before doing roof conduit. It varies 
> tremendously, from union shops doing PVC to hacks doing IMC, depending 
> upon local custom. We do like to make it sturdy though, as it is 
> subject to a fair amount of abuse over a 25 year life. We typically 
> fasten it down by attaching wooden (PT) spacers to concrete blocks. 
> Concrete block
> holds it in place, off the roof (cooler and better for drainage), but
> does not penetrate the roof.

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