a couple questions about raceways in an attic.

[rong111]

hi all.

in the midwest(usa) area the weather extremes wreak havoc on conduit in unheated attics. even if the attic has the proper r-value and the conduit is burried. what occurs is that the conduit acts as a "chimney" drawing in warm air from the heated area into the cold attic. the resulting condensation then freezes and as it warms in the attic it thaws and leaks into fixtures! i am aware of no cost effective way to solve this problem except one.

ok, the questions: obviously the conduit has rust on the inside. it is no where near rusted through. just surface brown powder corrosion.
does the presence of rust no matter how little, diminish the ground potential of the conduit in a system where it is used instead of a green wire?
i think maybe the ion that produces the galvonic action to cause the rust may be electro-chemically reactive? or am i just thinking too much

next question: the only way i know how to solve this problem is to stick a product called "pug- duct seal" into each and every conduit entrance into a j-box! this stuff is marketed for exactly this purpose. this is very common in the midwest climate. even in homes that are properly built and insulated. so i was wondering does the nec have anything to say about this pug stuff? it is basicly fire retardent "silly putty" that you stuff into the raceways and it never dries. if more wire needs to be pulled it pops right out. the idea is not to stop a leak, but to prevent warm air from entering the raceway. in this respect it does it's job wonderfully. even if the nec has nothing speciffacly to say about this practice, is it a good or bad idea in your guys opinions? if it is not great, what else could solve this problem that does not cost a fortune?


thank you,
ron g.

 

[iwire]

Re: a couple questions about raceways in an attic.

The NEC does cover this exact situation.

300.7 Raceways Exposed to Different Temperatures.

(A) Sealing. Where portions of a cable raceway or sleeve are known to be subjected to different temperatures and where condensation is known to be a problem, as in cold storage areas of buildings or where passing from the interior to the exterior of a building, the raceway or sleeve shall be filled with an approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve. An explosionproof seal shall not be required for this purpose.

I do a lot of work in walk in coolers and freezers, it is amazing how fast a fixture or switch box can fill with water if you do not plug the raceway.

We use duct seal for this.

 

[rong111]

Re: a couple questions about raceways in an attic.

thank you! i love this board and it's members! exactly the reinforcing answer i was looking for!

it surprises me that most of the homes around here are built without plugged raceways in this situation. and of course all of them start leaking. a neighbor called me over once when her smoke dect. was going off and there was no fire. it had like 8 ounces of water and ice in it! i just replaced 13 fixtures so i am going to plug them all now before they are destroyed again!
a lot of general contractors think simply burrying the conduit takes care of this. no way.

for some reason i didnt see that part of the nec when i looked. now that you pointed out the number of course i see it there

what do you think about the loss of ground potential in slightly rusted(discolered) conduit?
does the presence of ANY rust whatsoever require replacement of the entire run? or at what amount of rust does conduit need to be replaced? only when it is completely breached? i guess to satisfy myself i can hook a 60 watt lamp between my voltmeter and the conduit to see the current draw capacity.

thank you,
ron g.

[ October 17, 2003, 12:50 AM: Message edited by: rong111 ]