[RE-wrenches] Does a Neutral Count as a CCC
Ray Walters
ray at solarray.com
Sun Apr 24 20:26:35 EDT 2016
However, in this case, Peter's installing lots of 120 vac branch=20
circuits, so all of those neutrals will be carrying full current (unless=20
they are shared neutral circuits). Mike Holt's exception would apply to=20
240vac circuits if they had a neutral. Further, Holt's exception would=20
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=20
> 4-wire 3-phase 120/208V or 277/408V wye-connected system isn=E2=80=99t=20
> considered a current-carrying conductor.
>
> The neutral conductor of a 3-wire circuit from a 4-wire 3-phase=20
> 120/208V or 277V/480V wye-connected system is considered a=20
> current-carrying conductor.
>
> When a 3-wire circuit is supplied from a 4-wire 3-[phase wye-connected=20
> system, the neutral conductor carries approximately the same current=20
> as the ungrounded conductors.
>
> The neutral conductor of a 4-wire 3-phase circuit is considered a=20
> current-carrying conductor where the major portion of the neutral load=20
> consists of nonlinear loads. This is because harmonic currents will be=20
> present in the neutral conductor, even if the loads on each of the 3=20
> phases are balanced.
>
> Nonlinear loads supplied by 4-wire 3-phase 120/208V or 277/480V=20
> wye-connected systems can produce unwanted and potentially hazardous=20
> triplen harmonic currents (3rd, 9th, 15th, etc.) that can add on the=20
> neutral conductor. To prevent fire or equipment damage from excessive=20
> harmonic neutral current, the designer should consider increasing the=20
> size of the neutral conductor or installing a separate neutral for=20
> each phase. see 210.4(A) FPN, 220.61 FPN 2, and 450.3 FPN 2.
>
> Grounding (earthing) and bonding conductors aren=E2=80=99t considered cur=
rent=20
> carrying.
>
> For individual dwelling units or one-family, two-family, and=20
> multifamily dwellings, Table 310.15(B)(6) can be used to size 3-wire=20
> single-phase 120/240V service or feeder conductors (including neutral=20
> conductors) that serve as the main power feeder. Feeder conductors are=20
> not required to have an ampacity rating greater than the service=20
> conductors [215.2(A)(3)].
>
> Warning: Table 310.15(B)(6) doesn=E2=80=99t apply to 3-wire single-phase =
> 120/208V systems, because the grounded neutral conductor in these=20
> systems carries neutral current even when the load on the phases is=20
> balanced [310.15(B)(4)(6)]. For more information on this topic, see=20
> 220.61(C)(1).
>
> /Grounded Neutral Conductor Sizing./ Table 310.15(B)(6) can be used to=20
> size the grounded neutral conductor of a 3-wire single-phase 120/240V=20
> service or feeder that serves as the main power feeder, based on the=20
> feeder calculated load in accordance with 220.61.
>
> Because the grounded neutral service conductor is required to serve as=20
> the effective ground-fault current path, it must be sized so that it=20
> can safely carry the maximum fault current likely to be imposed on it=20
> [110.10 and 250.4(A)(5)]. This is accomplished by sizing the grounded=20
> neutral conductor in accordance with Table 250.66, based on the total=20
> 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=20
> <peter.parrish at calsolareng.com <mailto:peter.parrish at calsolareng.com>>=20
> 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=E2=80=99t care. In the end, there is no safety risk. So I=E2=80=
=99ll 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.=20
> 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=E2=80=9D PVC conduits, and I am curre=
ntly
> 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=E2=80=99t. 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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> --=20
> *
> James B. Rudolph*
> *Haleakala Solar* *
> *
> *Director of Construction*
> *NABCEP Certified PV Installer # 091209-155
> *
> *
> *
> *
> *
>
> *
> *
>
>
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