Penetrate roof with liquid tight ?

Status
Not open for further replies.

JJWalecka

Senior Member
Location
New England
I have a question...

Hi pathetically speaking,

Can you penetrate the metal decking of a roof with liquid tight flexible metal conduit? You would use a "Witch hat" that would be sealed by the roofing contractor.

Normally EMT or Rigid would be used to penetrate the roof the change over to liquid tight.

Feedback is encouraged
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Not speaking hypothetically, we have in the past wired roof top units that way. The roofer installs a pitch pocket and we bring our LFMC through it from a junction box in the ceiling below the roof.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I see no reason not to unless the ceiling below is a plenum. I don't believe one could use liquidtight in a plenum.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
weak link

weak link

There is, I believe, one weak link in using LFNC; that being it is normally a 60 deg C rated conduit, so technically speaking, the condutors would have to be uesed at their 60 rating. Often overlooked, but, I believe, technically correct.
 

celtic

Senior Member
Location
NJ
augie47 said:
There is, I believe, one weak link in using LFNC; that being it is normally a 60 deg C rated conduit, so technically speaking, the condutors would have to be uesed at their 60 rating. Often overlooked, but, I believe, technically correct.

From the commentary following 350.10
Liquidtight flexible metal conduit (LFMC) is intended for use in wet locations or where exposed to mineral oil, both at a maximum temperature of 140?F.

Does that mean a conductor is only good for the 60?C rating?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
temp rating

temp rating

celtic said:
From the commentary following 350.10


Does that mean a conductor is only good for the 60?C rating?


Thats my understanding
 

hillbilly

Senior Member
celtic said:
From the commentary following 350.10


Does that mean a conductor is only good for the 60?C rating?

That's a good question and one that I've never thought of.
Well maybe I have, but I don't remember ever considering it.

Does the temperature rating of the of the conduit limit the temperature rating of the conductors inside it to the conduits maximum?
Without looking, I say yes.
steve
 

iwire

Moderator
Staff member
Location
Massachusetts
I would check your job specifications if you have any.

It is common that the specs will require IMC or RMC for roof penetrations.

Personally I dislike LFMC up through a poured pitch pocket and I refuse to run it up through a rubber witches hat. IMO you setting your customer up for future leaks with the flexing of the witches hat / LFMC combination.
 

amptech

Senior Member
Location
Indiana
We usually come out the side of the curb the RTU sits on. Rubber roofers supply a few tubes of their special caulk for us to seal around the penetration if they aren't going to stick around. Haven't had one leak so far. We always use alum rigid conduit for feeding rooftops.
 

amptech

Senior Member
Location
Indiana
We usually come out the side of the curb the RTU sits on. Rubber roofers supply a few tubes of their special caulk for us to seal around the penetration if they aren't going to stick around. Haven't had one leak so far. We always use rigid aluminum conduit.
 

SmithBuilt

Senior Member
Location
Foothills of NC
A note on going thru the curb.

I've done it many times without a problem. But the last time the roofing co had to get the roof certified by the membrane manufacture for the warrenty. They would not certify due to the curb penetration. I refused to redo the electrical, so they had to do a pitch pocket around each one.

I still contend thru the curb is a better method, but the roofer wanted the rubber boot on a flat roof? Next time I will clarify with the roofer first.
 
Status
Not open for further replies.
Top