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

peter...@pobox.com

 

From: RE-wrenches [mailto:re-wrenches-boun...@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

 

From: RE-wrenches [mailto:re-wrenches-boun...@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

peter...@pobox.com

 

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