[RE-wrenches] Does a Neutral Count as a CCC

Mon Apr 25 07:04:03 PDT 2016

In addition to what is stated below, my understanding is that neutrals in
many commonly used inverter output circuits are not current carrying
conductors either. You’ll have to check with your inverter manufacturer to
be certain, however.

Best,

August

Luminalt

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
Behalf Of *James Rudolph
*Sent:* Saturday, April 23, 2016 11:59 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Does a Neutral Count as a CCC

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> 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

petertor at pobox.com

*From:* RE-wrenches [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

[image: Gradient Cap_mini]
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600

*From:* RE-wrenches [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

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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