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#84728 - 04/29/03 11:34 PM outside if under 2" concrete  
Cindy  Offline
Member
Joined: Jun 2001
Posts: 196
PDX, OR, US
230.6 says you can consider the conductors like they are outside if under 2" of concrete...

so is there a problem with having a meter on the outside of a building, and running emt under 2" of concrete to the main disco panel 50 feet inside the building?

considering the service entrance conductors as outside in this case, they meet 230.70a1 by being near the point of entry inside where they would come up in the emt into the panel.


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#84729 - 04/30/03 04:46 AM Re: outside if under 2" concrete  
nesparky  Offline
Member
Joined: Jun 2001
Posts: 642
omaha,ne
Cindy
EMT in or under a concrete floor is a not a good practice. It will rust out fairly quickly.
Also your local AHJ may have rules about how far in a service conductor may travel into the building.
I would install a service disco (c/b or fused) with the meter then the wire into the building is a feeder. Also would use PVC underground and thru the slab.


ed

#84730 - 04/30/03 05:49 AM Re: outside if under 2" concrete  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
RNC would be a better choice for the under ground and it's easy to work with, use a female adapter and change to a RMC 90 degree sweep to turn up to the panel then use either RMC, IMC or EMT from the sweep to panel.

If its encased or covered by 2" of concrete it is "outside" the building no mater how far you run it in the building.

Consider many commercial buildings, the electric rooms are located in the core of the building so window space for offices or whatever is not lost to the electric room.

The feeds leave a pad mount outside and go into the building 50-100 feet under the slab.

Many brownstones in Boston have underground services entering the basement but the architects on remodels have the service gear located on the first floor, so you can use the basement for a condo or apartment.

To do this we run RNC and encase it in two inches of concrete from the basement to the main switch.

I also work at a 3 story building that has a 13.8KV substation on the roof (the 3rd floor tenant has 3 - 3000 amp 480 volt services from there and a 4000 amp 208 service from another source, I can not say to much but our taxes paid for this), the 13.8KV feeders run inside the building encased in concrete from underground up through the building to the roof where they run across the roof in RMC.

As always check with the local inspector before spending money and time.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#84731 - 04/30/03 08:59 AM Re: outside if under 2" concrete  
US Coreman  Offline
Member
Joined: Mar 2003
Posts: 36
Illinois, USA
I must agree with the previous posts and add that in a discussion with another member, Russ M, he wrote :

This is out of the UL white book.

In general, galvanized steel electrical metallic tubing in contact with soil requires supplementary corrosion protection. Where galvanized steel electrical metallic tubing without supplementary corrosion protection extends directly from concrete encasement to soil burial, severe corrosive effects are likely to occur on the metal in contact with the soil.

Supplementary nonmetallic coatings presently used have not been investigated-

for resistance to corrosion.

I was looking for his opinion as a fellow inspector. It confirmwed mine, and since Russ has been doing this far longer than I, I was confident that he had the resources for substantiation,

I hope it helps.

Gregg


#84732 - 04/30/03 12:01 PM Re: outside if under 2" concrete  
wocolt  Offline
Member
Joined: Dec 2002
Posts: 110
I have seen EMT used that way or PVC, Rigid and it is ,IMO not a good idea. Only from the standpoint of having to do a re-vamp on it.
Alot of times they would put the service in the garage(double) and pipe into the basement maybe 30 feet away. I have seen often when the concrete cracked because of moisture and broke through the conduit and now the customer is getting water into the conduit and thus into the panel. One customer called me and wanted to know what to do, short of replacing the service. He wanted to drill holes in the bottom of the conduit in his basement to let the water out.
I strongly advised him against that idea but he went ahead and did it.
Alot of jobs are set up that way but theres gotta be a better way.

WmColt


#84733 - 04/30/03 12:49 PM Re: outside if under 2" concrete  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,878
NY, USA
I don't remember ever seeing an EMT service riser (on Long Island) that didn't look like this:

[Linked Image]

Of course, I don't know if any corrosion protection was applied or not, and typical services like this I've seen may be 30 yrs old.

Bill

[This message has been edited by Bill Addiss (edited 04-30-2003).]


#84734 - 04/30/03 09:53 PM Re: outside if under 2" concrete  
Cindy  Offline
Member
Joined: Jun 2001
Posts: 196
PDX, OR, US
its not my design, and actually we will use rnmc but i wanted opinions on the emt

anyway about the service entrance conductors, heres what i read.....

230.32 Protection Against Damage.
...service-lateral conductors shall be protected against damage... entering a building shall be installed in accordance with 230.6 "OR" protected by a raceway wiring method identified in 230.43.

sooooooo, that "OR" says you can even go with direct burial below a 2" concrete slab into a building or else they wouldnt have said put the "OR" as an option to a raceway?????


230.6 Conductors Considered Outside the Building... under any of the following conditions:
(1) Where installed under not less than 50 mm (2 in.) of concrete beneath a building or other structure
(2) Where installed within a building or other structure in a raceway that is encased in concrete or brick not less than 50 mm (2 in.) thick

about the emt, because rnmc seems to have more benefit, this is just for the sake of argument....

its allowed...
230.43 Wiring Methods...
Service-entrance conductors... the following methods: (5) Electrical metallic tubing

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

so do you use a special emt for this corrosion protection? doesnt all thin-wall have zinc based corrosion protection outside and a corrosion resistant organic coating on theinside? thanks


#84735 - 05/01/03 10:17 AM Re: outside if under 2" concrete  
nesparky  Offline
Member
Joined: Jun 2001
Posts: 642
omaha,ne
Yes EMT is permitted in concrete, and direct buried, but IMHO it is not a good idea. I have never seen anything that would protect it from corrosion. Thin wall steel does not need very long to rust out. Heck I have seen Rigid rusted thru. It just took longer.
Using RNC and changing over to RGS for the vertical riser is probably the best combination for what you describe. It will slow down the corrosion occurance the most.


ed

#84736 - 05/02/03 09:40 PM Re: outside if under 2" concrete  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,308
I had thought that the philosophy behind SEU being external, with a limited entry to residences, was to dictate the main disco for FF's.

So my bubble is burst here with industrial scenarios esentially hiding this path 'outside' the building, as well as out of view


#84737 - 05/02/03 10:41 PM Re: outside if under 2" concrete  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Small aside — One thing about soils: generally the more corrosive they are the lower resistance buried ground electrodes have.

Years ago an EC&M article discussed the particular tendency of corrosion where metal conduit passed from soil-to-air, concrete-to-air and soil-to-concrete.


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