Resi. feeder and service sizing

[hey_poolboy]

Just curious, how many of you use table 310.15 B6
in sizing resi feeders or services as opposed to the ampacity tables.

I know bids are tight and sometimes that will allow use of smaller stuff than the tables, but would you use the resi table in YOUR home?

 

[redfish]

Re: Resi. feeder and service sizing

On an average size home, I go 200A with a 200A can, a 200A midwest main disconnect, and a 200A main lug 40circuit panel, but to each his own.

 

[celtic]

Re: Resi. feeder and service sizing

The cost difference in material from a 150 to a 200 is minuscle...it costs more for me to do the load calculation...so everybody gets a 200A (unless it's a huge custom home).

 

[Jhr]

Re: Resi. feeder and service sizing

I use it all the time for residential single phase dwelling services and yes I would use it on my own house, why wouldn't you.

 

[hey_poolboy]

Re: Resi. feeder and service sizing

I was mostly referring to wire size as opposed to equipment or load calcs.

Services I usually do 2/0 for 200a.
Say I was running a 100a feeder to a garage, I usually use #2, where as 310.15 B 6 allows #4. I guess I just like to play it safe.

 

[iwire]

Re: Resi. feeder and service sizing

Originally posted by hey_poolboy:
Say I was running a 100a feeder to a garage, I usually use #2, where as 310.15 B 6 allows #4. I guess I just like to play it safe.

Actually it does not allow it.


Part of 310.15(B)(6)

....and feeder conductors that serve as the main power feeder to a dwelling unit...

The garage is not a dwelling unit.

 

[hey_poolboy]

Re: Resi. feeder and service sizing

Alright, you've got me there. :roll:
Maybe next time I should make sure I know what I'm talkin' about before I just make up topics for general discussion and entertainment.

Well, live and learn, and learn, and learn....

 

[George Stolz]

Re: Resi. feeder and service sizing

Had a chat today with an inspector (actually, the "I Am" from a couple weeks ago

 

[hurk27]

Re: Resi. feeder and service sizing

George The first three words in 310.15(B)(6) allow that installation.

For dwelling units,

Units is plural, more than one.
No where does it say it's only for one famliy dwelling.

 

[mc5w]

Re: Resi. feeder and service sizing

Actually, those rating assume 4 things:

1. The wire terminals are rated 75 degrees Celsius.
2. At maximum load the neutral conductor will be loafing and for practical purposes only 2 or 2.25 conductors will be carrying current.
3. The voltage drop is acceptable.
4. It is acceptable to run the service that hot.

For a very long time Cleveland Electric Illuminating Company had a rule that 100 amp and 110 amp underground services had to have 125 amp wiring. This was partly because underground services are harder to fix even if the service is in conduit.

What I have found is that a 100 amp residential service that is running central air, an electric stove, and an electric dryer tends to have short life if the wire size is #2 aluminum or #4 copper.

Since Home Depot and Lowe's have 200 amp SquareD main breaker panels at a resonable prices, I do not see how it is more economical to put in only 100 amps. Even if I can prove that a 100 amp servie will work I have to assume that they will have zero or 1 heavy appliance.

 

[George Stolz]

Re: Resi. feeder and service sizing

Whoops: one other stipulation: refer to the 2005 code.

 

[codeunderstanding]

Re: Resi. feeder and service sizing

I've used the notes to 310.15b6 for the main feeder to a subpanel in a garage. I have asked the ahj and he says it is basically a main power feed from the service to the subpanel. I think it kind of resembles Exhibit 310.8 in the hand book. What do you guys think?

 

[roger]

Re: Resi. feeder and service sizing

The AHJ is wrong.

Roger

 

[iwire]

Re: Resi. feeder and service sizing

Originally posted by codeunderstanding:
I've used the notes to 310.15b6 for the main feeder to a subpanel in a garage. I have asked the ahj and he says it is basically a main power feed from the service to the subpanel. I think it kind of resembles Exhibit 310.8 in the hand book. What do you guys think?

I think it is a violation.

Originally posted by iwire:
Part of 310.15(B)(6)

....and feeder conductors that serve as the main power feeder to a dwelling unit...

The garage is not a dwelling unit.

The feeder to a garage has to be sized per 310.16.

 

[George Stolz]

Re: Resi. feeder and service sizing

Originally posted by hurk27:
George The first three words in 310.15(B)(6) allow that installation.

Any other takers?

By the 2005, it's illegal to use 310.15(B)(6) for this, IMO. My book's in the truck, read the first line of the 2005 and see what you think.

 

[iwire]

Re: Resi. feeder and service sizing

Originally posted by georgestolz:

Originally posted by hurk27:
George The first three words in 310.15(B)(6) allow that installation.

Any other takers?

By the 2005, it's illegal to use 310.15(B)(6) for this, IMO. My book's in the truck, read the first line of the 2005 and see what you think.

You lost me George what's illegal.

 

[George Stolz]

Re: Resi. feeder and service sizing

My wife's booting me off:

The hint is the word "of" in the first line. See your reply in an hour or so.

 

[iwire]

Re: Resi. feeder and service sizing

Originally posted by georgestolz:
My wife's booting me off:

The hint is the word "of" in the first line. See your reply in an hour or so.

I think you are correct.

I also feel it was in violation for another reason, table 310.15(B)(6) is not a conductor rating table and is not to be used to figure parallel conductor runs.

Table 310.15(B)(6) is no more of a rating table than 240.4(D) is.

Both of those sections change the way we treat the conductors, they do not change the rating of the conductors.

 

[stars13bars2]

Re: Resi. feeder and service sizing

Wheather you call it a garage panel or a pool panel, etc.. I don't see where this is written in the code. What I do see 408.14 which describes the lighting and appliance panelboards that 310.15(B)(6)refers to. If it meets the lighting and appliance panelboard standard, I don't see how you can rule it out.

 

[iwire]

Re: Resi. feeder and service sizing

Originally posted by stars13bars2:
I don't see where this is written in the code. What I do see 408.14 which describes the lighting and appliance panelboards that 310.15(B)(6)refers to. If it meets the lighting and appliance panelboard standard, I don't see how you can rule it out.

Read the following section and pay attention to the part I made bold.


2002 NEC there are some changes for 2005

310.15(B)(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For dwelling units, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a 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 panelboard(s). The feeder conductors to a dwelling unit shall not be required to be larger than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22, and 230.42 are met.

It clearly states for dwelling units.