2008 code change? Table 310.15b6

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NolaTigaBait

Senior Member
Location
New Orleans,LA
did the 2008 code no longer allow you to use this table for feeders that aren't the main source of power for a dwelling...Was this table allowed to be used before 2008 or was this always the case?
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
so, we don;t know for sure reason why im asking is the house that im talking about upgrading service and sub panels, has #4-3 nm run to a sub panel in the 1st and 2nd floor, a sub in the garage and for some reason they ran a #4-3 for the air handler and the 2 cond units....im wondering if i change the service, should i derate to a 70 amp breaker, whereas, they have them all on 100 breakers!
 

Inspectorcliff

Senior Member
Location
Colorado
did the 2008 code no longer allow you to use this table for feeders that aren't the main source of power for a dwelling...Was this table allowed to be used before 2008 or was this always the case?
ChSection 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6). ALSO LOOK AT 338.10.B4a6; For the 2008 Code, the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load.
Provided a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or feeder conductors that supply the main power feeder to a dwelling unit. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.
Exhibits 310.8 and 310.9 illustrate the application of 310.15(B)(6). In Exhibit 310.8, the reduced conductor size permitted is applicable only to the service-entrance conductors run to each apartment from the meters. In Exhibit 310.9, the reduced conductor size permitted is also applicable to the feeder conductors run to each apartment from the service disconnecting means,eck out the Handbook, I think, No would be applicable here until you get to #6 conductors.
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
ChSection 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6). ALSO LOOK AT 338.10.B4a6; For the 2008 Code, the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load.
Provided a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or feeder conductors that supply the main power feeder to a dwelling unit. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.
Exhibits 310.8 and 310.9 illustrate the application of 310.15(B)(6). In Exhibit 310.8, the reduced conductor size permitted is applicable only to the service-entrance conductors run to each apartment from the meters. In Exhibit 310.9, the reduced conductor size permitted is also applicable to the feeder conductors run to each apartment from the service disconnecting means,eck out the Handbook, I think, No would be applicable here until you get to #6 conductors.


you lost me here...what are you trying to say?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
ouch.... Seemed unnecessary.

Can you fuse it down to the proper size. If the load allows just change the breaker.
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
If I understand your question correctly or part of it anyways, I would size the breakers for the A/C to the size called for on the unit. Sounds like they just had some extra wire.
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
they ran a 4-3 with a ground to the attic....then to a 8 space can...came out of there for the 15kw heat strips and out to the cond unit outside with it looks like two 6-2's....they might have had some spare wire, sure...the job just didn't look that nice...and they have the #4-3 on a 100 amp breaker and im not sure what the min ampacities are on the units
 

220wire

Member
on one panel, i don't think it'll be a prob, but the other has 40 circuits....so, im not really sure what the demand is

if you are not sure what the demand is, then how can you know what you need? Isn't it the electricain's job to figure for the load(s) being served? Or maybe you should ask an engineer. Those guys are really smart!
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
if you are not sure what the demand is, then how can you know what you need? Isn't it the electricain's job to figure for the load(s) being served? Or maybe you should ask an engineer. Those guys are really smart!

well probably b/c no matter what the load is....there is still an undersized feeder running to this panel....so, if i can make due, i will....
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
I submitted a proposal to revert to the 2005 language, as I think this is the worst change in the 2008.

im kinda confused here....are you saying in 05 that #4 was good for 100 amps even if it wasnt supplying 100 of the load?....several others have said that this ISN'T new for '08, it was just clarified
 

ryan_618

Senior Member
im kinda confused here....are you saying in 05 that #4 was good for 100 amps even if it wasnt supplying 100 of the load?....several others have said that this ISN'T new for '08, it was just clarified

That is exactly what I am saying. The fact that the terms "main power feeders" and "panelboards" are written in the plural in 2005 tells me that it was allowed.
 

ryan_618

Senior Member
As currently written, I could have a 200A service with 4/0 AL as long as everything comes off of that panel. So lets say I have 2 air conditioners in that subpanel. If I were to decide I wanted I wanted to put them out at me service disconnect, 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???
 

NolaTigaBait

Senior Member
Location
New Orleans,LA
As currently written, I could have a 200A service with 4/0 AL as long as everything comes off of that panel. So lets say I have 2 air conditioners in that subpanel. If I were to decide I wanted I wanted to put them out at me service disconnect, 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???

that's exactly what i was thinking!....
 

ryan_618

Senior Member
that's exactly what i was thinking!....

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".
 
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