Still trying to make sense of SER wire size.

[stickboy1375]

Because this is supposed to be a forum to post questions and LEARN, and that is what I am trying to do here is learn, I think we all are. What good does it do anyone to "just change your ways" if you are doing so blindly?

Your asking why the code panel made a certain decision, I doubt anyone here was there when they made it... sorry...
I wish I knew also.... but any answer would just be a guess...

 

[racerdave3]

Your asking why the code panel made a certain decision, I doubt anyone here was there when they made it... sorry...
I wish I knew also.... but any answer would just be a guess...

I agree with you there that there may not be anyone here that was there when they made the decision, but I know we have some really sharp people on here that could offer some insight into the facts of their decision. I certainly don't claim to understand everything that they require us to do, and many things may not seem right to me at first, but when someone can explain the reasoning behind it, it can shed more light on things and make me understand where it is coming from. Just looking for a full understanding of things to continue to become a better electrician.

 

[jwelectric]

I'll ask this question yet again..........BUT WHY??? And I don't want to hear "because the Code says so" I want to know what everyone thinks on their own about this discussion and the discrepencies. I know in reality it may seem petty to be dickering back and forth about a measly 10 amps, but I still just cannot understand the reasoning why the same cable can be used for 90 amps in one situation and 100 in another. The FACTS are that it is the same cable, made from the same material, with the same insulation, so what is the justification to provide 2 different values? It just seems much more complicated than it should be!

Race Dave I like seeing the number 3 beside your name. I am a #3 fan myself. I believe in my heart that he is still racing somewhere.

To address your question I went to the ROPs and found this;

6- 83 - (310-15(b)(6)): Reject
SUBMITTER: Leonard F. Devine, Jr., W. Palm Beach County
Bldg & Zoning, FL
RECOMMENDATION: Revise text to read as follows:
(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For dwelling units, and detached residential garages, 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, or detached residential garage, 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), and the feeder conductors to a dwelling unit or detached residential garage 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 Sections 215.2, 220.22, and 230.42 are met.
SUBSTANTIATION: By adding this text, it would put the garage in the same category as the dwelling. If the garage is attached to the dwelling and you had a panel located in the garage you would allow one to derate the feeder.
PANEL ACTION: Reject.
PANEL STATEMENT: A detached residential garage may include a workshop and thus would not provide the diversity similar to a dwelling unit.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 11
VOTE ON PANEL

http://www.nfpa.org/assets/files/pdf/A280-310.pdf?src=necdigest

 

[LarryFine]

Dave, from Mikes snippet, it's obvious that a main feeder can depend on load diversification more or less guaranteeing that the connected load rating will never be reached under normal conditions, while the same can't be said for a sub-panel's feeder.

Why? The garage example gives a hint as to why: I can see the relatively localized load possible on a sub-panel approaching its feeder's capacity. After all, to the service, a feeder is a MWBC; the separation of neutral and EGC is a characteristic of this.

To address your question I went to the ROPs and found this;

Mike, if you don't mind, how does one "go to the ROP's" and find something like this?

 

[jwelectric]

Mike, if you don't mind, how does one "go to the ROP's" and find something like this?

The link I posted takes you to the ROP that I posted.

Go to www.nfpa.org and then Codes and Standards then Code Development Process look for ROP the archives are usually at the bottom of the page.

 

[LarryFine]

Cool! Thanx!

 

[George Stolz]

Here is a snippet from a little project I'm working up, with direct links.

The ROPs and ROCs can be found at this link to the NFPA website.
The NFPA Manual of Style (basically, the rules for writing rules) can be found at this link.
A downloadable proposal form is here.
A downloadable comment form is here.

Edit to add: I agree with the above, load diversity is the reason that 310.15(B)(6) only applies to dwelling units. Non-dwelling units would need load diversity demonstrated (calculated) by an engineer, IMO.

 

[Dinspect]

Dinspect

Dinspect

The N.F.P.A should be making the code as a reference so average joe could have better understanding of the code causing less confusion in appling it to his or her situation.

Remember carefully read the wording in 215.2(a)(3),110.14(c)

 

[dnem]

The N.F.P.A should be making the code as a reference so average joe could have better understanding of the code causing less confusion in appling it to his or her situation.

Remember carefully read the wording in 215.2(a)(3),110.14(c)

How about so average inspector could have better understanding of the code causing less confusion in applying it to inspections ?

 

[Dinspect]

You missed the point!

 

[Dinspect]

Check Alcan wire co. Their data cut sheet states #2 al ser can be installed on a 100 amp breaker as long as it is being feed from a single phase 120/240 volt system for a dwelling.