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Old 05-02-2016, 09:35 PM   #1
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Have a 200 amp panel with main c/b in commercial application. Ran 4/0 al.. Foreman says need 250mcm . 4/0 rated 180 amp, next largest standard size breaker is 200 amp. Load is very light. Any thoughts?
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Old 05-02-2016, 11:31 PM   #2
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use 4/0 al all the time for 200a service
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Old 05-02-2016, 11:37 PM   #3
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Foreman is correct.
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Old 05-02-2016, 11:45 PM   #4
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310.15(b)(7) says its goob for 200a. is there a place that says its different for commercial?
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Old 05-03-2016, 12:46 AM   #5
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Originally Posted by papaotis View Post
310.15(b)(7) says its goob for 200a. is there a place that says its different for commercial?

310.15 only mentions dwellings, hence the special exception for residential. Commercial does not permit a reduction.
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Old 05-03-2016, 12:51 AM   #6
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Agreed
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Old 05-03-2016, 06:05 AM   #7
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Why would 240.4(b) not apply?

4/0 aluminum would be fine under the "next standard size" rule.
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Old 05-03-2016, 06:26 AM   #8
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Is it 3 phase? If so, I believe you need to derate because it's over 3 current carrying conductors of you are carrying a neutral.
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Old 05-03-2016, 06:28 AM   #9
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Why would 240.4(b) not apply?

4/0 aluminum would be fine under the "next standard size" rule.
That is a tad conflicting ......~CS~
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Old 05-03-2016, 05:59 PM   #10
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Is it 3 phase? If so, I believe you need to derate because it's over 3 current carrying conductors of you are carrying a neutral.
Is that neutral really counted as a CCC?
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Old 05-03-2016, 06:33 PM   #11
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As long as the calculated load doesn't exceed 180 amps, you can use a 200 amp breaker.
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Old 05-03-2016, 06:57 PM   #12
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That is a tad conflicting ......~CS~
240.4(B) basically states that if the value in the allowable ampacity table does not correspond to one of the standard values listed in table 240.6(A), then it's ok to use the next higher standard rating.

This applies to circuits of 800 amps or less.
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Old 05-03-2016, 07:19 PM   #13
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Originally Posted by Forge Boyz View Post
Is that neutral really counted as a CCC?
If it carries amperage, which would be the imbalance between the 3 phases then yes, it is a CCC.
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Old 05-03-2016, 08:27 PM   #14
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Ok, 1st. Thanks for all the comments. This building is one story, notary office in front and apartment in rear. Have a 2 gang metered main with 2- 200 amp breakers. According to the inspector, I can feed the apartment panel with 4/0 al. but need to feed the notary with 250mcm. He said the next higher breaker doesn't apply to commercial applications. What really makes this strange is that the apartment load is much higher than the notary.
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Old 05-03-2016, 08:54 PM   #15
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Originally Posted by Electek inc View Post
Ok, 1st. Thanks for all the comments. This building is one story, notary office in front and apartment in rear. Have a 2 gang metered main with 2- 200 amp breakers. According to the inspector, I can feed the apartment panel with 4/0 al. but need to feed the notary with 250mcm. He said the next higher breaker doesn't apply to commercial applications. What really makes this strange is that the apartment load is much higher than the notary.
As long as you can calculate and show the load to be 180 amps or less, 4/0 aluminum on a 200 amp breaker is legal, commercial or otherwise. By the NEC anyway. Ask him to show you an amendment that says otherwise.
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Old 05-03-2016, 09:04 PM   #16
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Calculated load is 85 amps. I've appealed 2 other calls from this agency and had both of them were reversed. Kinda have to walk softly with them, might just install 250's and call it good.
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Old 05-03-2016, 09:20 PM   #17
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3/0 copper will be more expensive but easier to pull in existing conduit if you must change it out.
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Old 05-03-2016, 09:33 PM   #18
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Quote:
Originally Posted by TRurak View Post
Quote:
Originally Posted by Forge Boyz View Post
Is that neutral really counted as a CCC?
If it carries amperage, which would be the imbalance between the 3 phases then yes, it is a CCC.
In this case the neutral would not be counted as a current carrying conductor. See commentary.


Part (B)(4) In the determination of conduit size, neutral conductors must be included in the total number of conductors because they occupy space as well as phase conductors. A completely separate consideration, however, is the relation of neutral conductors to the number of conductors, which determines whether ampacity derating must be applied to conductors in a conduit, as follows.
Neutral conductors that carry only unbalanced current from phase conduc- tors (as in the case of normally balanced 3-wire, single-phase or 4-wire, 3-phase circuits supplying resistive loads) are not counted in determining ampacity derating of conductors on the basis of the number in a conduit, as described. A neutral conductor used with two phase legs of a 4-wire, 3-phase system to make up a 3-wire feeder is not a true neutral in the sense of carrying only current unbalance. Such a neutral carries the same current as the other two conductors under balanced load conditions and must be counted as a phase conductor when more than three conductors in conduit are derated.
The technical basis for the full-current loading on the 3-wire feeder neutral from a wye system is based on phasor analysis that shows that if you have a cir- cuit consisting of two phase conductors and a neutral from a wye distribution with 100 A of line-to-neutral current on each phase conductor, perfectly bal- anced, the neutral will carry 100 A as well. Note that the identical load profile connected to a single-phase distribution would result in a zero ampere loading on the neutral. Further, as the load on one of the phase conductors in this example decreases, the load on the neutral does decline slightly, reaching a minimum of about 87 A (1/2 3 highest load) and then rising again to 100 A when the load on the more lightly loaded phasor reaches zero and we are left with 100 A in what has become effectively a two-wire circuit. Therefore, these neutrals are effectively fully loaded at all times and must be counted accord- ingly. By the way, the minimum loading in these cases occurs when one phasor carries 100 A and the other is carrying one-half that amount or 50 A.
Because the neutral of a 3-phase, 4-wire wye branch circuit or feeder to a load of fluorescent, metal-halide, mercury, or sodium lamp lighting or to electronic data processing equipment?the so-called information technology equipment?or any other nonlinear load will carry harmonic current even under balanced loading on the phases (refer to 220.61), such a neutral is not a true noncurrent- carrying conductor and must be counted as a phase wire when the number of conductors to arrive at an ampacity derating factor is determined for more than three conductors in a conduit. As a result, all the conductors of a 3-phase, 4-wire branch circuit or feeder to a fluorescent load would have an ampacity of only 80 percent of their nominal ampacity from Table 310.16 or other ampacity table. Because the 80 percent is a derating of ampacity, the conductors must be protected at the derated ampacity value.
Figure 310-23 shows four basic conditions of neutral loading and the need for counting the neutral conductor in loading a circuit to fluorescent or mercury ballasts, as follows:
Case 1?With balanced loads of equal power factor, there is no neutral cur- rent, and consequently no heating contributed by the neutral conductor. For purposes of heat derating according to the Code, this circuit produces the heating effect of only three conductors.
Case 2?With two phases loaded and the third unloaded, the neutral carries the same as the phases, but there is still the heating effect of only three conductors.
Case 3?With two phases fully loaded and the third phase partially loaded, the neutral carries the difference in current between the full phase value and the partial phase value, so that again there is the heating effect of only three full-load phases.
Case 4?With a balanced load of fluorescent ballasts, third-harmonic cur- rent generation causes a neutral current approximating phase current, and there will be the heating effect of four conductors. Such a neutral conductor must be counted with the phase conductors when the load-current limitation due to conduit occupancy is determined, as required in part (C) of part (B)(4).
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Old 05-03-2016, 10:03 PM   #19
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Quote:
Originally Posted by micromind View Post
240.4(B) basically states that if the value in the allowable ampacity table does not correspond to one of the standard values listed in table 240.6(A), then it's ok to use the next higher standard rating.

This applies to circuits of 800 amps or less.

But does code mention services? I could be wrong, but my understanding is that the next size up does not apply to services?
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Old 05-03-2016, 10:11 PM   #20
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Service conductors are sized by the calculated load from what I understand. You could add up the main breakers and it will usually far exceed the wire size.

That is why I don't understand why 277 is mentioning the calculated load as it pertains to this question. It should have nothing to do with it. It is not the service.

Side note: Once you go over 800 amps the breaker sizes take bigger jumps, so you have to go next size down.

Last edited by cabletie; 05-03-2016 at 10:15 PM.
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