[RE-wrenches] Does a Neutral Count as a CCC
Ray Walters
ray at solarray.com
Sun Apr 24 17:26:35 PDT 2016
However, in this case, Peter's installing lots of 120 vac branch
circuits, so all of those neutrals will be carrying full current (unless
they are shared neutral circuits). Mike Holt's exception would apply to
240vac circuits if they had a neutral. Further, Holt's exception would
not be applicable on any off grid system that was 120 vac only.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 4/24/2016 12:58 AM, James Rudolph wrote:
> Straight from Mike Holt:
>
> *Neutral Conductor*
>
> The neutral conductor of a 3-wire single-phase 120/240V system, or
> 4-wire 3-phase 120/208V or 277/408V wye-connected system isn’t
> considered a current-carrying conductor.
>
> The neutral conductor of a 3-wire circuit from a 4-wire 3-phase
> 120/208V or 277V/480V wye-connected system is considered a
> current-carrying conductor.
>
> When a 3-wire circuit is supplied from a 4-wire 3-[phase wye-connected
> system, the neutral conductor carries approximately the same current
> as the ungrounded conductors.
>
> The neutral conductor of a 4-wire 3-phase circuit is considered a
> current-carrying conductor where the major portion of the neutral load
> consists of nonlinear loads. This is because harmonic currents will be
> present in the neutral conductor, even if the loads on each of the 3
> phases are balanced.
>
> Nonlinear loads supplied by 4-wire 3-phase 120/208V or 277/480V
> wye-connected systems can produce unwanted and potentially hazardous
> triplen harmonic currents (3rd, 9th, 15th, etc.) that can add on the
> neutral conductor. To prevent fire or equipment damage from excessive
> harmonic neutral current, the designer should consider increasing the
> size of the neutral conductor or installing a separate neutral for
> each phase. see 210.4(A) FPN, 220.61 FPN 2, and 450.3 FPN 2.
>
> Grounding (earthing) and bonding conductors aren’t considered current
> carrying.
>
> For individual dwelling units or one-family, two-family, and
> multifamily dwellings, Table 310.15(B)(6) can be used to size 3-wire
> single-phase 120/240V service or feeder conductors (including neutral
> conductors) that serve as the main power feeder. Feeder conductors are
> not required to have an ampacity rating greater than the service
> conductors [215.2(A)(3)].
>
> Warning: Table 310.15(B)(6) doesn’t apply to 3-wire single-phase
> 120/208V systems, because the grounded neutral conductor in these
> systems carries neutral current even when the load on the phases is
> balanced [310.15(B)(4)(6)]. For more information on this topic, see
> 220.61(C)(1).
>
> /Grounded Neutral Conductor Sizing./ Table 310.15(B)(6) can be used to
> size the grounded neutral conductor of a 3-wire single-phase 120/240V
> service or feeder that serves as the main power feeder, based on the
> feeder calculated load in accordance with 220.61.
>
> Because the grounded neutral service conductor is required to serve as
> the effective ground-fault current path, it must be sized so that it
> can safely carry the maximum fault current likely to be imposed on it
> [110.10 and 250.4(A)(5)]. This is accomplished by sizing the grounded
> neutral conductor in accordance with Table 250.66, based on the total
> area of the largest ungrounded conductor [250.24(C)(1)].
>
> aloha and happy trails...
>
>
> On Thu, Apr 21, 2016 at 10:28 AM, Peter Parrish
> <peter.parrish at calsolareng.com <mailto:peter.parrish at calsolareng.com>>
> wrote:
>
> William,
>
> I agree about the subpanel in the house situation. The customer is
> a bit eccentric, and I have tried to bring him around. And I have
> explained to him that his approach will be more expensive. He
> doesn’t care. In the end, there is no safety risk. So I’ll plan
> for 4 branch circuits per conduit and take the 0.70 derating.
>
> - Peter
>
> Peter T. Parrish, Ph.D.
>
> President, SolarGnosis
>
> 1107 Fair Oaks Ave.
>
> Suite 351
>
> South Pasadena, CA 91030
>
> (323) 839-6108 <tel:%28323%29%20839-6108>
>
> petertor at pobox.com <mailto:petertor at pobox.com>
>
> *From:*RE-wrenches
> [mailto:re-wrenches-bounces at lists.re-wrenches.org
> <mailto:re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of
> *William Miller
> *Sent:* Thursday, April 21, 2016 10:25 AM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Does a Neutral Count as a CCC
>
> Peter:
>
> I think it is a mistake to not locate a sub-panel in the house.
> Running branch circuits 45 feet to a separate building is not
> efficient or practical.
>
> Voltage drop: 1% VD is a choice, not a requirement. Code requires
> 3% on feeders and 5% cumulative on AC branch circuits. I like to
> use 1% for average voltage drop for PV because of the cost of
> wasted PV energy. I am more lax on AC circuits. If I calculate a
> PV feeder for 1%, that drop will occur only occasionally, when
> peak solar is achieved. Analyze your load or charging profiles
> and look for a calc that provides the chosen VD for average use.
> Analyzing PV energy curves over a given day, approximately 50% of
> the energy is under the bell curve.
>
> Neutrals are current carrying. Try powering a 120VAC load without
> one and you will see what I mean.
>
> William Miller
>
> Gradient Cap_mini
> Lic 773985
> millersolar.com <http://www.millersolar.com/>
> 805-438-5600 <tel:805-438-5600>
>
> *From:*RE-wrenches
> [mailto:re-wrenches-bounces at lists.re-wrenches.org
> <mailto:re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of
> *Peter Parrish
> *Sent:* Thursday, April 21, 2016 8:57 AM
> *To:* 'RE-wrenches'
> *Subject:* [RE-wrenches] Does a Netral COunt as a CCC
>
> I am working with a customer who is doing a complete remodel and
> addition to his house: stripped to the open studs and floor
> joists, and rafters. Not a wire in the house. We have designed a
> 14.4 kWp PV system with 16 kW of storage for backup and load
> shifting. The main panel, inverters, critical load subpanel and
> batteries are all going to be in the garage which is about 45 feet
> from the house. The customer and I have identified the critical loads.
>
> The GC is running conduit from the main house to the garage. I
> have been given seven (7) 1-1/2” PVC conduits, and I am currently
> doing conduit fill, ampacity and voltage drop calculations for the
> branch circuits that represent the critical loads.
>
> So I have two questions:
>
> (1)Should I stick to a <1% voltage drop on all circuits?
>
> (2)Do 120 V neutrals count as current carrying conductors? I think
> they do, but the electrician stated quite emphatically that they
> didn’t. I thought that the derating calcs for CCCs were based
> solely on ohmic losses and phasing was not taken into account.
>
> Does the NEC provide guidance on this latter situation?
>
> -Peter Parrish
>
> Peter T. Parrish, Ph.D.
>
> President, SolarGnosis
>
> 1107 Fair Oaks Ave.
>
> Suite 351
>
> South Pasadena, CA 91030
>
> (323) 839-6108 <tel:%28323%29%20839-6108>
>
> petertor at pobox.com <mailto:petertor at pobox.com>
>
>
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> --
> *
> James B. Rudolph*
> *Haleakala Solar* *
> *
> *Director of Construction*
> *NABCEP Certified PV Installer # 091209-155
> *
> *
> *
> *
> *
>
> *
> *
>
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