Buried EMT

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macmikeman

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Planet macmikeman
I came into the trade a fairly long time ago. Pvc electrical conduit was invented and in use, but not for very long at that point. Some local area's near where I worked were not allowing it to be used yet. At my first place of employment they would paint lap seal on emt and bury it direct in the soil. I doubt any of those installs made it this far, and are completely rusted away to powder by now.
 
Dennis Alwon

Dennis Alwon

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Retired Electrical Contractor
macmikeman said:
I came into the trade a fairly long time ago. Pvc electrical conduit was invented and in use, but not for very long at that point. Some local area's near where I worked were not allowing it to be used yet. At my first place of employment they would paint lap seal on emt and bury it direct in the soil. I doubt any of those installs made it this far, and are completely rusted away to powder by now.
Click to expand...


Yeah when I workwed for a contractor at IBM in Kingston, NY we buried 2" rigid but painted it with Tar...
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Fulthrotl said:
1984, hotel meridian across from john wayne airport. {Edited to remove the name of the electrical contractor said to be responsible for the installation described below.}

1/2" emt home runs, they'd run 100'+ in a post tension slab,
and then turn down with a red dot 90 above where the panel
would go. they'd turn up wherever, in emt. no GRC where it
would exit the pour. concrete listed fittings. no duct tape.

the concrete paddle machines would grab them during finishing,
and twist them off, leaving the stub looking like the twisted end
of a cigarette that i'm sure the general foreman who thought all
this up was smoking.

3/4" emt home runs, 100' plus, stubbing up into a riser that went
up six floors, feeding that plug in every room. 3/4" emt in the bottom
of the box, 3/4" emt out the top of the box, a 1/2" out the side of the
box to feed a plug down the wall, full house in the bottom, full house
out the top, and a device in the box.... and it's a 104 box.

why no, i'm not a big fan of emt in the slab...... i spent the first two
months working there fixing broken 1/2" emt stubs, and found one
that was tie wired to a post tension cable, that i nicked one day
while dissecting around the emt, not realizing that it was a post tension
cable until it became less tense, all of a sudden.

they make a loud bang, by the way.
Click to expand...

When that happens, you don't even have time to go "Oh, s**t!" before it's all over.
 
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anthonyddjr

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Location
US
rlundsrud said:
I have seen EMT fitting that stated they were listed for use in concrete if they were wrapped in duct tape. It was a long time ago, and I honestly can't remember the name of the manufacturer, but I kind of laughed when I read it.
Click to expand...
As dumb as it sounds, set screw , steel fittings say suitable for concrete. I have , nor will I ever try this. All it takes is one bad joint, ie: tape joint and bam, a lost raceway. I

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anthonyddjr

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I am sure there are a few guys in here, that have been in the craft for far longer than my baby 30yrs. However, I think we can all agree on something. Some of the codes make no sense at all. This is one of those applications that although is allowable by code. Makes no sense time, nor has it ever. I have come across many times over the years where EMT was either used in a slab( hotels are great examples) , and for direct burial. And I have never come across any of these two applications where there was not rust in the conduit. Likewise, I have never been successful in pulling wire out of a run of EMT in either application. Especially if its been down there for several years. I am sure it was a great application at first, however over the years of the conduit in the ground, surrounded by cool dirt or concrete, and the air within the conduit being warmer due to the ambient temperature of the wire. Condensation occurs and despite the conduit having a galvanized coating, the scrapes from pulling wire make a great breeding ground for rust. And of course after 5yrs or so, depending on temps and such the wire laughs at you struggling to attempt getting it out because there was a fault and needs to be replaced. If the Specs say it is OK, just run PVC. If not, bid it right and run Ridged and use anti corrosion tape or paint it with such. They honestly should take another look at that code. It really, in my humble opinion, doesn't seem like a good application.

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anthonyddjr

Member
Location
US
jumper said:
What about column 3, other approved raceways?

And yes it can be buried. Says so in 358.10(B)

(B) Corrosion Protection.
Ferrous or nonferrous EMT, elbows, couplings, and fittings shall be permitted to be in-
stalled in concrete, in direct contact with the earth, or in
areas subject to severe corrosive influences where protected
by corrosion protection and approved as suitable for the
condition.

Horrible idea though.
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Yes it is, for all the safety and preventive we do, and all the NEC provides for us to follow. Running EMT in concrete, or dirt makes little sense. Especially if you have ever seen what happens in a hotel to the raceways after several years of prolonged use. Not much common sense in that coding for sure. But as Mike Holt says " for test purposes the answer is 358.10(b). Lol

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norcal

Senior Member
The feeder to my pumphouse used to be 1 1/4" EMT buried in dirt, it was replaced years ago but the EMT is still there & has a unused phone line in it, when some remodeling was done in 1994, some of it was excavated & was surprised how good it looked, it came as salvage from a Titan missile base built in the late '50's, early '60's, and buried in the mid 1970's, PVC is more suited for the purpose though.



There are 3 old Titan bases around here, 1 near the Sutter Buttes https://en.wikipedia.org/wiki/Sutter_Buttes , another near Beale AFB, and the one locally that was a place for trysts & smoking dope, + a few rescues when "explorers" got hurt. http://www.siloworld.net/851st SMS/BEALEAFB.HTM https://en.wikipedia.org/wiki/851st_Strategic_Missile_Squadron But that's enough for the thread hijack.
 
kwired

kwired

Electron manager
Location
NE Nebraska
anthonyddjr said:
As dumb as it sounds, set screw , steel fittings say suitable for concrete. I have , nor will I ever try this. All it takes is one bad joint, ie: tape joint and bam, a lost raceway. I

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Click to expand...

Forget to tighten a compression fitting or cement a PVC fitting and you could have a similar problem.

In Jumpers quote it says ferrous or non ferrous EMT - though most all EMT one ever sees is ferrous, should you ever run into stainless EMT you ultimately would have better corrosion protection then you would with ferrous RMC.

Standard ferrous EMT works fine in most slabs above grade the moisture just normally isn't there. If slab is outdoors or subject to frequent washdown that may change.
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have seen EMT buried before. Never really thought much of the idea. Don't think much of the idea of burying rigid either. They will both rust through eventually. PVC is the appropriate UG raceway IMO.

OTOH, since you have to use conductors suitable for wet areas in UG raceways, I am not real sure it makes any difference as long as one is not relying on the EMT or conduit to be the EGC.
 
peter d

peter d

Senior Member
Location
New England
Over the past year I've dealt with several 1960's era buildings that were wired with RMC in the slab, and of course TW or RHW wire in them. Long story short, the conduits were rotting out and shorting, so we ended up having to refeed over head which is no easy task. We all know there is little to no chance of pulling rubber and cloth conductor out of rotted conduit. Obviously, PVC was not in use in the 1960's but given that metal raceways can have a short life in adverse soil conditions where PVC does not, PVC is the obvious choice to me.
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
peter d said:
Over the past year I've dealt with several 1960's era buildings that were wired with RMC in the slab, and of course TW or RHW wire in them. Long story short, the conduits were rotting out and shorting, so we ended up having to refeed over head which is no easy task. We all know there is little to no chance of pulling rubber and cloth conductor out of rotted conduit. Obviously, PVC was not in use in the 1960's but given that metal raceways can have a short life in adverse soil conditions where PVC does not, PVC is the obvious choice to me.
Click to expand...

around here.... huntington beach used to be called oildale, and it was an apt name.
ground rods here are stainless steel. GRC conduit just disappears into the dirt.
i've looked at feeders for pool pumps that were put in during the 70's, the pipe
stops a few inches under the dirt, and it's just bare wire. you can't even tell there
was ever any pipe around the wire.

while this place is a bit extreme, it's neigh on impossible to pull wire out of GRC
conduit after a while. yellow 77 hardens up, and the condensation inside the conduit
causes it to rust from the inside, swelling up and filling the conduit.

i pulled some 2/0 out of a 2" GRC pipe about 250' long that had been there for 30
years around here, and the only way it came out of the pipe was 'cause there was
a crane handy, and we looped the conductors and used wire clamps on them, and
poured half a gallon of poly water into each end of the pipe a few days before.
the strain gauge on the crane was running 12-15 tons to move it.

old pipe around here, just gets redone.
 
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