Gary,
The snow loads that structural engineers design to are a worst-case scenario.
It is true that snow tends to slough off of PV arrays quicker than your normal
roof. However, if there is a major snow event, especially if it starts at night
(this recent blizzard on the East Coast would be a g
Ray,
The "solar constant" -- the average irradiance value at the edge of the Earth's
atmosphere -- is about 1360 W/m2. See the wikipedia article:
http://en.wikipedia.org/wiki/Solar_constant
You're pushing the edge of what's possible if you're getting 1400 W/m2. There
could be a slight calibra
From: Allan Sindelar
To: JRQ
Sent: Sunday, August 12, 2012 4:00 PM
Subject: Re: [RE-wrenches] GTWB outage monitor question
Jeff,
Great in theory...but I'm missing a few details as to how to put
it into practice.
Can you tell me where I might find a relay with a 175A co
Louis,
Can Enphase inverters be positively grounded? I wasn't aware that they could.
Otherwise you have an equipment mismatch problem that can't be overcome under
the listing of the modules and the inverters.
Jeffrey Quackenbush.
From: Louis Woofenden
To:
Allen,
If it's a backup system, the batteries aren't going to draw a significant
amount of current until the grid goes down. If you can find a DC relay that
triggers after, say, 2A or 3A, install it on the battery conductors. The relay
should come on, then, when the grid goes down, but not when
Eric,
This doesn't sound so bad. The Voc seems a little low (10 modules in series at
44.2 Voc would be 442 Voc), but you haven't provided irradiance or temperature
information, so that's hard to assess. As far as the drop from Voc to Vmp,
consider:
35.4 Vmp / 44.2 Voc = 80%
280 Vmp / 375 Voc =
I'm in the process of NABCEP re-certification and I have two complaints about
their process:
1. In the last year, NABCEP added a requirement for 3 customer surveys as
documentation of projects completed. This was released just after I had left a
job doing installations to do consulting overseas
I had a similar problem working in San Diego. SDG&E insisted that no taps could
be performed in an enclosure unless the contractor could supply documentation
that the enclosure was specifically listed for a tap, or if an electrical
engineer supplied stamped drawings of the tap. I never did a pro
I've been wondering about this since I read over the 2011 code:
Are there any listed DC arc-flash products on the market yet, or scheduled to
come to market within the next year?
Also: will arc-flash protection come in the form of breakers that need to be
installed externally, or will it be som
Now that Enphase has chosen to use Amphenol H4 connectors, does mean that none
of the Enphase inverters are, technically, listed to be connected to modules
with MC4 connectors (basically any module)?
It seems like Multi-Contact is more interested in keeping their product
proprietary, so they ca
Larry,
A Sunny Boy won't feed any power directly at a generator on the main panel: the
AC on either side of the Sunny Island is separately derived, and it's my
understanding that the SI can command the SBs through the CAT V link to
throttle back if loads aren't sufficient. Wouldn't the Sunny Is
ly derived system.
In the end, I don't believe it matters whether we consider the DC
side to be separately derived or not, as 250.30 only applies to AC,
and 690 is now fairly clear about bonding and grounding requirements
regardless.
Ray Walters
On 1/24/2012 9:10 PM, JRQ
Separately-derived means that there is physical isolation between two circuits
in the same electrical system – usually this involves two circuits connected by
a transformer
The DC side is separately derived in a transformer-based PV inverter. Most
grid-tie inverters have a DC main bonding jumpe
You can't go wrong with a new "solar-ready" service panel. You can tell the
customer that, in addition to enabling a larger solar system, it is a safety
upgrade.
Otherwise you're going to have to backfeed one of these subpanels or the one of
the 100A mains inside the house.
Do the mains in #2
vent horizontal runs shouldn't be
> problem, but what happens when the power vent fails?
> It will fail. I've seen the bearings wear out on one and another that
> failed when insects got into the blades and gummed it up to the point
> that the motor stalled.
>
> Kent
delar
al...@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com
On 12/31/2011 7:59 AM, JRQ wr
Wrenches,
I'm looking at a potential battery backup system wtih a 200 AH @48V flooded
battery bank in the basement electrical room of a 3 story building. There is a
window in the electrical room. The batteries will be located about 10' from an
outdoor wall. The building is all reinforced concre
load on the conductor in an earlier email. Maybe I didn't spell this
out explicitly enough, but if there are parallel circuits coming off this
conductor, say, for instance, a tap, this also would not apply.
Jeffrey Quackenbush
____
From: Ray Walters
To: JRQ
without a main service
panel, just a main switch
Date: Fri, 23 Dec 2011 09:41:24 -0700
From: Ray Walters
To: JRQ
HI Jeffrey;
Electricity certainly can flow in both directions on a conductor
(unless they've installed huge diodes). If there is a short circuit
in the smallest conducto
org] On Behalf Of JRQ
Sent: Friday, December 23, 2011 3:51 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Landing into a sub-panel without a main
servicepanel, just a main switch
Yes, if there is a distribution block and several subpanels are fed from the
same point downline from the main disconn
Yes, if there is a distribution block and several subpanels are fed from the
same point downline from the main disconnect, then what I'm describing would
not be applicable. The other subpanels function as loads with respect to the
distribution block. The same if there are any taps on the load si
_____
From: Ray Walters
To: JRQ ; RE-wrenches
Sent: Friday, December 23, 2011 4:45 AM
Subject: Re: [RE-wrenches] Landing into a sub-panel without a main service
panel, just a main switch
I'm not a huge fan of this 120% rule myself, but if you're going to apply it
p
But wait, there are no loads at the 200 A disconnect. The idea behind the
limitation in the "20% rule" is that if you have power coming from a main to a
set of loads on a bus and also power from a backfed PV breaker to the same bus,
that bus could theoretically draw the sum of the main and the P
William,
I actually prefer to use Unirac L-brackets for mounting J-boxes. Sometimes I'll
use the Enphase one because it comes with the Enphase whip (and therefore I
save paying $2.75 on an extra L-bracket). However, I find the L-brackets to be
sturdier and less visible.
Jeffrey Quackenbush
NAB
I'd avoid using the metal conduit as the only bond in your equipment grounding
from the roof down to other equipment. If the GEC is bonded to the rest of the
equipment grounding system at a point on the ground, then of course it can
double as the EGC. Otherwise, if you don't want to use a separa
Last time I checked there was no Mac version available. I can't even use their
new tool.
Jeffrey Quackenbush
NABCEP-certified PV installer
Ninja Solar
From: William Miller
To: RE-wrenches
Sent: Friday, December 2, 2011 11:45 PM
Subject: Re: [RE-wrenches] SMA
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