#4 copper wire

[tonyi]

Re: #4 copper wire

There's some practical mechanical reasons why a larger wire might occur at the end of a run...like needing something that will fit under the lugs of whatever you're hooking to.

 

[don_resqcapt19]

Re: #4 copper wire

Roger,
It is my opinion that the code permits the #4 to be protected at 100 amps for this application. Maybe that is not what the CMP intended when the section was written, but it is what the words say. The definition of main power feeder does not say anything about supplying the main power to the dwelling. The definition controls the rule and as long as the feeder is on the load side of the service OCPD and as long as it feeds a lighting and appliance branch circuit panel, then the reduced wire sizes are permitted by the code.
Don

 

[roger]

Re: #4 copper wire

Don, this is another occasion where we will have to disagree, but I must ask, when did you change your opinion, this was not your stance in November on another forum.

Roger

 

[websparky]

Re: #4 copper wire

Humm...

Hi Guys,

I think I have to agree with Roger on this one.

2002 NEC Handbook

If 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 any feeder conductors that supply the main power feeder to a dwelling unit.
This section permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6) even if other loads, such as ac units and pool loads, are fed from the same service. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.
Exhibits 310.7 and 310.8 illustrate the application of 310.15(B)(6).

In Exhibit 310.7, the reduced conductor size permitted is applicable to the service-entrance conductors run to each apartment from the meters.

In Exhibit 310.8, the reduced conductor size permitted is also applicable to the feeder conductors run to each apartment from the service disconnecting means, because these feeders carry the entire load to each apartment.

 

[bennie]

Re: #4 copper wire

I am losing track of who thinks what now.

My statements were that all panel feeds in a dwelling are allowed to be sized by the reduced Table.

I thought most were in opposition. Maintaining that a feeder had to be larger than the service entrance conductors.

I guess I am losing it

 

[tonyi]

Re: #4 copper wire

IMO, this one needs an official NFPA interpretation. The presense of the plurals on "feeder(s)" and "panelboard(s)" suggests Don's everything downstream type reading might be valid.

However, this same language could also validly describe the "1st layer only" scenario if the feeders/panels were tapped off the main.

There's also scenarios like a single uninterrupted feeder with slew of taps off to different MLO panels.

Curiously the article used the term disconnect in the singular. Imagine the ramifications for an old split bus panel - any feeders from its multiple disco's won't get the bennefit of this article!

 

[hurk27]

Re: #4 copper wire

Now Dave take another feeder from one of the apartment breaker panel to yet another 100 amp panel. Now does this set of feeders fall under 310.15(B)(6)?
I'm just trying to learn as I have always thought that you never need to run a wire larger than the than the wire feeding it. as to what purpose would it serve? (Not talking about VD) as if there was any overload to this last set of feeders wouldn't it overload the first set too? and if this was possible then the first set can be overloaded just from the main panel. Now I would under stand if the first panel was a 200 amp but not a 100a feeding a 100a.

I believe that the wording should read:
The feeder conductors to or in a dwelling unit shall not be required to be larger than their service-entrance conductors.

[ January 03, 2004, 02:17 AM: Message edited by: hurk27 ]

 

[don_resqcapt19]

Re: #4 copper wire

Roger,

Don, this is another occasion where we will have to disagree, but I must ask, when did you change your opinion, this was not your stance in November on another forum.

I have flipped on this one a few times. I think that the section needs revision. Using the term "main power feeder" and then defining that term in a way that does not say anything about being the "main" supply to the dwelling unit is the cause of the confusion. I believe that the panel's intent is that the reduced sizes cannot be used for "subpanels", but the code wording does not support the panel's intent. I believe that the wording in the code book, permits the reduced sizes for all dwelling unit lighting and appliance branch circuit panel feeders.
Don

 

[fishin' electrician]

Re: #4 copper wire

As earlydean pointed out, this feeder is within, not to the dwelling.

Even though all feeders to panels within a dwelling meet the 310.15(B)(6) definition for a main power feeder, the definition only applies to "feeder conductors that serve as the main power feeder to a dwelling unit".

 

[pierre]

Re: #4 copper wire

Sometimes our own language defeats us before we have even started, and 310.15(B)(6)is another example of how we can take what is meant and read it differently.

The intent as I have been taught for this is to permit the Main Power Feeders to be kept at the same size as the service conductors. All feeders leaving the service equipment are to be regarded as feeders, feeders following all other rules governed by the NEC.
The reason there is a plural (s), is some of the larger size services are paralleled.
The fact that Don, with the knowledge that he has, has changed his mind on this subject helps to show the language needs to be changed, to try and suit the myriad of people who now read (and try to understand)the NEC.

Regardless of the language the intent is to have the Main Power Feeders sized according to 310.15(B)(6), and all other feeders sized accordingly [not with the use of 310.15(B)(6)].

For those who did not know, or some who may have forgot, table 310.15(B)(6)has restrictions as to the type of conductors and cable types that can be used, AC and NM are not permitted for this use.
The first printing of the NEC does not have the list at the top of the table, and the errata for the 2002 NEC can be found on the web.

Pierre

 

[jxofaltrds]

Re: #4 copper wire

May I say that only the main feeder is defined here.

I did not think that the service lateral conductors were under the NEC's authority.

Now if the supplying utility brings the service lateral or service entrance conductor to the structure in lets say 2/0 alum. And since the feeders do not have to be larger than the service entrance conductors, can I "feed" my 200amp panel with 2/0 alum???

Remember this section starts out "shall be permitted".

Mike P.