[RE-wrenches] conductors and the 120% rule

[Brian Mehalic]

If the subpanel is at the end if the feeder, and there are no taps in between the main and the sub then I don't see any reason that the conductors need to be any larger than 200 A as there is no where on the feeder conductors where grid and PV current will be additive. 

The changes in 705.12 in 2014 address this in large part. 

Brian

> On Mar 4, 2014, at 2:41 PM, "Kirk Herander" <kirk at vtsolar.com> wrote:
> 
> Solaredge 20 kw, 480 3-phase. Good point, but that may be irrelevant. The feed-in subpanel is also powering unrelated loads, which use the neutral as a conductor from the main panel. So 4 conductors from the main.
>  
> Kirk Herander
> VT Solar, LLC
> dba Vermont Solar Engineering
> NABCEPTM Certified Inaugural Certificant
> NYSERDA-eligible Installer
> VT RE Incentive Program Partner
> 802.863.1202
>  
> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allen Frishman
> Sent: Tuesday, March 04, 2014 4:32 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] conductors and the 120% rule
>  
> what inverter(s) are you using?    In many cases the Neutral is not considered a Current Carying Conductor by the Manufacturer and therefore you only have 3 CCC.
> Al Frishman
> AeonSolar
> (917) 699-6641 - cell
> (888) 460-2867
> www.aeonsolar.com
>  
> On Mar 4, 2014, at 4:20 PM, Kirk Herander wrote:
> 
> 
> Approx.. 50 – 60ft.
>  
> Kirk Herander
> VT Solar, LLC
> dba Vermont Solar Engineering
> NABCEPTM Certified Inaugural Certificant
> NYSERDA-eligible Installer
> VT RE Incentive Program Partner
> 802.863.1202
>  
> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ray Walters
> Sent: Tuesday, March 04, 2014 4:05 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] conductors and the 120% rule
>  
> What is the length of the conduit to the subpanel? That will determine whether to apply the derates.
> 
> 
> R.Ray Walters
> CTO, Solarray, Inc
> Nabcep Certified PV Installer, 
> Licensed Master Electrician
> Solar Design Engineer
> 303 505-8760
> On 3/4/2014 1:34 PM, Kirk Herander wrote:
> Whether or not a further derate has to be applied is the killer here, as I am working with existing panels and conductors. In an old Code Corner(HP140) J. Wiles goes through a similar scenario and calls out the allowable current rating and conductor in 310.15, but makes no mention of applying additional derate factors. The .8 derate for 4-6 conductors(l1,l2,l3, & n) will put the existing 4/0 cable between feed-in and main panel at 208 amps, less than the allowable 217. I’d hate to need to upsize the wire to 250 mcm.
>  
> Kirk Herander
> VT Solar, LLC
> dba Vermont Solar Engineering
> NABCEPTM Certified Inaugural Certificant
> NYSERDA-eligible Installer
> VT RE Incentive Program Partner
> 802.863.1202
>  
> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason Szumlanski
> Sent: Tuesday, March 04, 2014 2:57 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] conductors and the 120% rule
>  
> Both the bus and conductors need to be rated for 217 amps minimum. As you mentioned, the bus is not a problem. The way I interpret it, the conductor size required would be after derate factors are applied. The rating of the conductor is ultimately dependent on the derate factors.
>  
> If you can locate your subpanel adjacent to the main distribution panel, you may be able to use Exception #3 to 310.15(B)(2) by connecting the panels with a short nipple. I assume you are just looking at a number of conductor derate and not an ambient temperature derate.
>  
> Jason Szumlanski
> Fafco Solar
> 
>  
> <image001.jpg>
>  
> 
> On Tue, Mar 4, 2014 at 12:05 PM, Kirk Herander <kirk at vtsolar.com> wrote:
> Hello,
> I have a 225 amp 3-phase main lug sub-panel protected by a 200 amp breaker. My inverter breaker feeding the sub panel is 60 amps. So 225 a bus x 1.2 = 270 amps. That’s less than the sum of the two breakers of 260 amps, so no issue there. The conductors between sub and main panel have to be rated for at least 260/1.2 = 217 amps, correct? Is this 217 amps before or after derating the conductor?
>  
>  
> Kirk Herander
> VT Solar, LLC
> dba Vermont Solar Engineering
> NABCEPTM Certified Inaugural Certificant
> NYSERDA-eligible Installer
> VT RE Incentive Program Partner
> 802.863.1202
>  
>  
> 
> 
> 
> 
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