EMT exposed outside and underground

[jschultz]

I am reviewing a job by another engineering firm, They have a 1200A service. They have (4) sets of 4#350KCMIL, in a 2 1/2" C. The wire type called for is thwn-2 or xhhw-2 in their specifications. They have sched 40 pvc, emt, imc, and rigid listed in their specifications.

From my calculations, the only way it fits in a 2 1/2"C is if the conduit is EMT.

I have two questions regarding EMT for this installation:
1.The commentary from the 1999 NEC for 348-4(b) states that generally galvanized steel EMT installed in contact with soil requires supplementary corrosion protection. Is this accurate in your experience?

2. 348-5 (1) states that EMT is not allowed where electrical metallic tubing will be subject to severe physical damage. This installation is going from a CT cabinet to a pad mounted transformer. So there will be a couple feet exposed from the CT cabinet to the where it enters the ground. A riding lawnmower could be driving by this area. Is this considered "subject to severe physical damage"?

 

[roger]

Re: EMT exposed outside and underground

Take a look at annex C, I don't have my 99 right now but, as far as 02 IMC will work.

There is no true definintion of "severe physical damage" in the NEC.

Roger

 

[jschultz]

Re: EMT exposed outside and underground

You are right about the annex. I never use the annex. I always calculate them by hand.

from table 5
THWN-2 350KCMIL is 0.5242 sq in. x 4 = 2.0968 sq in
From table 4
IMC 2.5"C is good for 2.054" at 40%.

2.0968 is greater than 2.054.

The annexes are not part of the official code. Therefore the calculations above would be correct and the annex has a mistake in it.

 

[roger]

Re: EMT exposed outside and underground

You are right about the annexes not being an official part of the code EXCEPT in this case, where chapter 9 makes annex C part of the code.

See Notes to Tables (1)

Roger

[ March 15, 2004, 04:44 PM: Message edited by: roger ]

 

[don_resqcapt19]

Re: EMT exposed outside and underground

Roger,
In my opinion the note in Chapter 9 does not change 90.3.
Don

 

[roger]

Re: EMT exposed outside and underground

Don, in my opinion it does.

Roger

 

[tom baker]

Re: EMT exposed outside and underground

The note to 90.3 on the annex was added to the 2002 text to make it clear the annexs are not enforceable, it was missing from the 99 version. It was added to the 96 version as inspectors were trying to enforce examples in annex D.

 

[bob]

Re: EMT exposed outside and underground

Roger
At the top of Annex C the is a note as follows:
"This annex is not part of the requirements of the NFPA document but is included for informational purposes only"

 

[roger]

Re: EMT exposed outside and underground

Bob, I agree with that as far as the annexes on their own, but when we have a note in an official article directing us to Annex C it is giving permission to use the annex as part of the code in that particular case.

If we are going to say that note (1) in Chapter 9 can't be used as worded, what other parts of Chapter 9 or the NEC are not to be used as worded?

There is no mention in note (1) of chapter nine that in it's self it is only for reference.

Roger

 

[drmoody]

Re: EMT exposed outside and underground

Conduit fill aside. It has been my (and most people?s) experience as an electrician and an engineer, there?s no such thing as an overkill when it comes to conduit size. It certainly would be easier to find parts for 3? conduit and there is a good chance they are cheaper. I would not use EMT underground unless you can cathodically protect it?which is added, unnecessary cost.

Brian

 

[roger]

Re: EMT exposed outside and underground

Brian, besides wasting natural resources running 3" verses 2.5" is pretty expensive for the customer.

I have a job going right now with 26 runs of 2.5" EMT for a total of 3200'. Forgetting about all the incidentals and just looking at the conduit, compression steel connectors, and compression steel couplings, the difference in price per todays prices is roughly $2,660.00. This would be greater in IMC prices.

BTW I've never had a problem readily (just walking into the supply house) getting 2.5" conduit of any type except robroy, 3.5" is a little more trouble in smaller areas.

I do agree, I wouldn't run EMT underground.

Roger

[ March 16, 2004, 06:45 PM: Message edited by: roger ]

 

[jschultz]

Re: EMT exposed outside and underground

Notes to tables number 7
"When calculating the maximum number of conductors permitted in a conduit or tubing, all of the same size, the next higher whole number shall be used to determine the maximum number of conductors permitted when the calculation results in a decimal of 0.8 or larger."

So i guess according to code, you could actually put 4#350 in a 2.5" imc. But engineering wise, I would never make it that close of a fit. Especially when you throw two 90 degree bends into it, and the fact that it is a service entrance, why make it a difficult pull when you can put in a 3" conduit and make it an easy pull, where there is less chance of stressing or wrecking the conductors.