SER question

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augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
It will solve nothing , and I fear we will not resolve the problem here in the Forum, but since it's been a long while, this is the reasoning prersented by a member of CMP1
"215.2 and 310.15(B)(6) are what they are. 310.15(B)(6) allows a "rating" of 200 amperes for 4/0 aluminum conductors. This "rating" is not an allowable ampacity such as is provided in Table 310.16 but is
what it is - just a rating. Therefore, again, everything being equal
215.2(A)(3) states that "Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors." However, we are not equal where SE cable is utilized as the feeder wiring method to the secondary distribution panelboard inside the dwelling. See
338.10(B)(4)(a) that states "a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334." Note that the exclusion of 334.80 per the 2005 NEC is not excluded in the 2008 NEC in this section. This is because the code panel believes that SE cable is susceptible to having the same conductor heat dissipation problems as NM cable when run in the interior of buildings in attics and walls and especially where such cable is embedded in insulation. Therefore, 4/0 aluminum SE cable has to be sized from the 60-degree ampacity column of Table 310.16 which only allows it to have an allowable ampacity of 150 amps. Therefore, if the calculated load is 180 amps the 4/0 aluminum cable would not be acceptable and a 300 kcmil aluminum conductor at 190 amperes' would be
required per Table 310.16. Again, all things are not equal between the
service on the exterior of the dwelling and the feeder run through the interior of the dwelling

 
F

FrancisDoody

Senior Member
Location
Durham, CT
As Augie has presented to all of us. The 2005 code excluded temperature from the calculations. The 2008 limits the ampacity by enforcing the temperature limitations on conductors
 
Dennis Alwon

Dennis Alwon

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Gus has presented an interpretation by a cmp member. I still say that the words are not there to support that. It is merely his opinion. I agree it makes no sense to allow ser given the temp. rating. I am just stating that the NEC is not stating what this CMP member reasons the meaning to be.

Remember I also had a CMP member tell a group of 700 EC's that the white wire in a 14/3 nm cable could be used as the return to the light. When I showed him the words in the NEC that contradicted his view he refused to admit he was wrong. Fortunately 2 other CMP members, who were present, agreed with me.
 
augie47

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
I highly respect Dennis and his viewpoint, as I respect the thinking provided by the CMP member. I've been present when NFPA personnel have supported my view point but not substantiated it, and I've witnessed experts provide logical input as Dennis has. I feel it's an issue that will not be resolved until the CMPs provide clear wording to remove any vagueness.
We all know it is impossible for the Code to address every contingency but I wish items of this magnitude would be clarified. From what I have seen so far of the 2011 the issue is not resolved.
It seems it becomes an AHJ issue and even then I have been attempting to get an "offical" stand from the Director of Electrical Inspections for the State of TN for over a year and it's still being discussed.
 
M

masterselectric

Member
It is a residential dupex, we are installing a 3 gang meter socket, 2 for the apartments and one for a detached garage. I was planning on # 1 AL SER cables on 100 Amp breakers but was wondering what the deal was with #1/#2 AL conductors....can #2 be used with 100 amp breakers. There is no load concerns as they are 1 bedroom apartments with electric ranges. On single family dwellings, I know #2 SEU is used for service entreance cables at 100 amps
 
jwelectric

jwelectric

Senior Member
Location
North Carolina
338.10 is broke into two parts. Part (A) deals with type SE and USE when being used as a service conductor and Part (B) addresses type SE and USE when it is being used as a feeder or branch circuit.

My point being that the diversity in amperage load would be based on the use of the cable. As long as it is being used as service entrance conductors then 334 or 340 does not come into play at all see 338.10(A)

If the cable is being used as a feeder or branch circuit then 338.10(B) comes into play. For inside installations see Part II of 334 where we find the 60 degree requirement.
If the cable is being used outside the requirements of Part II of 340 and again the 60 degree rule.
 
jwelectric

jwelectric

Senior Member
Location
North Carolina
iwire said:
Mike we were wondering about you just the other day. :)
Click to expand...

Thank you Bob for the thought, all is well on the home front and work is wide open with little or no time for myself.

The sad truth of the matter is that the more people that draw unemployment the more work I have. I am now teaching more than most full time instructors.

Also not being heard from does not mean that I am not around lurking in the back ground.
 
L

LENewbie

Member
If I can jump in to this thread and ask a question please. I am racking my brain with the whole SEU and 60C issue. I have read and re-read and can someone point me in the direction where it says SEU has to be rated 60C. Example.

What size conductor for a 10KW resi heat??? I am using the SEU for a branch circuit
 
raider1

raider1

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Staff member
Location
Logan, Utah
LENewbie said:
If I can jump in to this thread and ask a question please. I am racking my brain with the whole SEU and 60C issue. I have read and re-read and can someone point me in the direction where it says SEU has to be rated 60C. Example.

What size conductor for a 10KW resi heat??? I am using the SEU for a branch circuit
Click to expand...

In the 2008 NEC SE cable used as interior wiring must comply with all the installation requirements of Part II of Article 334 including 334.80 which limits the ampacity used for SE cable to the 60 degree column of Table 310.16. (See 338.10(B)(4)(a) 2008 NEC)

Chris
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
So, if the calculated load is below 180a, the 4/0 SER can still be used and protected by a 200a breaker, or is the 300mcm required?
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
My question is really several parts:

1a. What's the smallest al SER we can use one 200 breaker on (200a svc)?

1b. What's the smallest al SER we can use two 200a breakers on (320a svc)?

2a. What's the largest breaker we can use to protect one 4/0 al SER (200a svc)?

2b. What's the largest breakers we can use to protect two 4/0 al SER's (320a svc)?
 
Dennis Alwon

Dennis Alwon

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Location
Chapel Hill, NC
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Retired Electrical Contractor
LarryFine said:
My question is really several parts:

1a. What's the smallest al SER we can use one 200 breaker on (200a svc)?

1b. What's the smallest al SER we can use two 200a breakers on (320a svc)?

2a. What's the largest breaker we can use to protect one 4/0 al SER (200a svc)?

2b. What's the largest breakers we can use to protect two 4/0 al SER's (320a svc)?
Click to expand...
Sorry but what is svc?
 
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