2008 code change? Table 310.15b6

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NolaTigaBait

Senior Member
Location
New Orleans,LA
Its like I told a guy at a class I was teaching a few weeks ago. This change should have had a flag thrown. There was no holding, no pass interference, no false start...but it is just plain stupid. Sometimes you have to throw a flag and blow this whistle and say "this is stupid".

it was a false start...
 

jwelectric

Senior Member
Location
North Carolina
, I would be putting less load on the feeder circuit, but now I have to make the wires bigger? Thats the stupidest thing I have ever heard in my life. Less load equals bigger wires???

Would you ever have to install feeders larger than the SE conductors?

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. ........................................... The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.


I disagree with you statement that this is the stupidest thing, it is my opinion that nothing has changed in that section it was just made clearer.
 

ryan_618

Senior Member
I disagree with you statement that this is the stupidest thing, it is my opinion that nothing has changed in that section it was just made clearer.

You are saying that when the code used to say feeder(s) to a panelboard(s), that this the same as feeder to a panelboard?

I can't look at words being changed from plural to singular and think that nothing has changed.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Would you ever have to install feeders larger than the SE conductors?
.

lets take a situation where you install a 200 amp "feed thru" service panel.
You supply that panel with a 4/0 AL Se cable per 310.15(B)(6), you feed a HVAC unit with a branch breaker from the "feed thru"anel and then extend a service cable to an interior panel for the balance of the dwelling load.
With the changes in Art 338, the extended SE cable feeding the interior panel would now have to be a 250kcmil AL, larger than the SE.
Correct ??
 

M. D.

Senior Member
I think this little sentance says quite a bit

The feeder conductors to a dwelling unit shall not be
required to have an allowable ampacity rating greater than their service entrance
conductors

so if I had a #2 Al service with a 100 amp MB panel I cannot run a #2 sub panel and protect it at 100 amps ...
to a dwelling is not the same as in a dwelling
 

jwelectric

Senior Member
Location
North Carolina
You are saying that when the code used to say feeder(s) to a panelboard(s), that this the same as feeder to a panelboard?

I can't look at words being changed from plural to singular and think that nothing has changed.

?05
conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboards(s).

?08
conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies,

What has changed other than we no longer have lighting and appliance panels?
 

jwelectric

Senior Member
Location
North Carolina
lets take a situation where you install a 200 amp "feed thru" service panel.
You supply that panel with a 4/0 AL Se cable per 310.15(B)(6), you feed a HVAC unit with a branch breaker from the "feed thru"anel and then extend a service cable to an interior panel for the balance of the dwelling load.
With the changes in Art 338, the extended SE cable feeding the interior panel would now have to be a 250kcmil AL, larger than the SE.
Correct ??

What is the next to last sentence found in 310.15(B)(6)?

"The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."

So the answer to your question is "incorrect"
 

jwelectric

Senior Member
Location
North Carolina
Very seldom (if ever) are there service entrance conductors in the area that I work in. The utility privdes underground conductors, and the service equipment/meter are outdoors in a common enclosure.

Then I would ask you if I chose to install a riser what size would it be required to be. What ever you say is the size to my feeders.
 

jwelectric

Senior Member
Location
North Carolina
I think this little sentance says quite a bit



so if I had a #2 Al service with a 100 amp MB panel I cannot run a #2 sub panel and protect it at 100 amps ...
to a dwelling is not the same as in a dwelling

From the main disconnect to the main panel would be the feeder to that panel. The key here is found in these words;
For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
lets take a situation where you install a 200 amp "feed thru" service panel.
You supply that panel with a 4/0 AL Se cable per 310.15(B)(6), you feed a HVAC unit with a branch breaker from the "feed thru"anel and then extend a service cable to an interior panel for the balance of the dwelling load.
With the changes in Art 338, the extended SE cable feeding the interior panel would now have to be a 250kcmil AL, larger than the SE.
Correct ??


I agree I think this is correct. Notice that the section does not say the feeder need not have a larger conductor than the SE conductors. It states it need not have a larger ampacity. Since the 250 se cable ampacity is now limited because of art.338 then I believe this would need to be done to be code compliant.
 

M. D.

Senior Member
From the main disconnect to the main panel would be the feeder to that panel. The key here is found in these words;
For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit.

You either misunderstood my post or I gave a rotten example of my meaning... I was talking about the feeder between the the dist. and the sub dist. panel . 100 amp #2 Al. to dist. panel fine ,.. #2 Al. between dist. panel and sub panel 100amp not fine. So in this case the second feeder would have to be larger than the SE and the first feeder,.. No???


sub-panel%202%20cr.jpg
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
You either misunderstood my post or I gave a rotten example of my meaning... I was talking about the feeder between the the dist. and the sub dist. panel . 100 amp #2 Al. to dist. panel fine ,.. #2 Al. between dist. panel and sub panel 100amp not fine. So in this case the second feeder would have to be larger than the SE and the first feeder,.. No???


sub-panel%202%20cr.jpg

thats why it doesn't make sense..its ok for the ENTIRE load to have a #2 feed the panel, but when you add a sub panel, it has to be bigger...this doesn't make any sense
 

jwelectric

Senior Member
Location
North Carolina
lets take a situation where you install a 200 amp "feed thru" service panel.
You supply that panel with a 4/0 AL Se cable per 310.15(B)(6), you feed a HVAC unit with a branch breaker from the "feed thru"anel and then extend a service cable to an interior panel for the balance of the dwelling load.
With the changes in Art 338, the extended SE cable feeding the interior panel would now have to be a 250kcmil AL, larger than the SE.
Correct ??
I agree I think this is correct. Notice that the section does not say the feeder need not have a larger conductor than the SE conductors. It states it need not have a larger ampacity. Since the 250 se cable ampacity is now limited because of art.338 then I believe this would need to be done to be code compliant.


215.2 Minimum Rating and Size.
(A) Feeders Not More Than 600 Volts.
(3) Individual Dwelling Unit or Mobile Home Conductors. Feeder conductors for individual dwelling units or mobile homes need not be larger than service conductors. Paragraph 310.15(B)(6) shall be permitted to be used for conductor size.
 

jwelectric

Senior Member
Location
North Carolina
You either misunderstood my post or I gave a rotten example of my meaning... I was talking about the feeder between the the dist. and the sub dist. panel . 100 amp #2 Al. to dist. panel fine ,.. #2 Al. between dist. panel and sub panel 100amp not fine. So in this case the second feeder would have to be larger than the SE and the first feeder,.. No???


sub-panel%202%20cr.jpg

yes I agree that between the two distribution panels a #2 aluminum SE-R cable would require a maximun 75 amp overcurrent device.
From the main disconnect to the first distribution panel then a #2 aluminum SE-R would be compliant with 215.2(A)(3)
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
Doesn't your first point conflict with your previous post? 215.2 says dwelling feeder conductors don't have to be larger than the service conductors. So why would a 75A breaker be required on the feeder between the Distribution Panel and the Distribution Sub Panel? I would think 215.2 supercedes NEC 338 and allow a 100A breaker on the feeder assuming a 100A service.
 
That one thing this is getting " silly " here but what I heard they did change the tempture rating on the SE conductors.

I know they are rated at 75?C no question asked but now with new 2008 NEC code they threw that rating out of the window now we have to treat the SE just like NM cables are and they are rated at 60?C that why it really affect it.

Just look at both 75?C and 60?C chart and see the diffrence there.

Merci,Marc
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
No matter how you want to interpret 310.15(B)(6) it has never applied to Type NM cable.

I don?t have a problem with the reduced conductor sizes only applying to the main feeders since I have always interpreted it this way. I do think having to use the 60C column for SE cable is ridicules especially for larger (100+ amp) residential feeders.
 

jwelectric

Senior Member
Location
North Carolina
Doesn't your first point conflict with your previous post? 215.2 says dwelling feeder conductors don't have to be larger than the service conductors.
No I believe that you have left part of the statement out. What it says is,

Feeder conductors for individual dwelling units or mobile homes
It doesn?t say all feeder conductors


So why would a 75A breaker be required on the feeder between the Distribution Panel and the Distribution Sub Panel? I would think 215.2 supercedes NEC 338 and allow a 100A breaker on the feeder assuming a 100A service.
It could have something to do with all those percentages that are allowed in a service calculation but not allowed in a feeder calculation.
 
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