To my understanding the 156% on PV source and output circuits is related to
the ability of PV to deliver more than rated and be continuous.
Therefore, the wire has to be able to carry this current, so now the
temperature and fill corrections are applied to find the wire capable of the
156%.
I
Here's my challenge to all of you that want to design for 1% or 1.5%
voltage drop all the time:
Take a 50-ft circuit carrying 40 amps at 12 volts, going to a C40
charge controller, select your wire size for 1% or 1.5% loss. You know
that's not a practical solution. I know that it makes more se
Erika,
You should refer to NEC 690.8 this information. There are two issues
that contribute to the 1.56 factor. First is that the maximum current
from the PV array is considered the short circuit current multiplied by
1.25 to account for higher than standard irradiance such as cloud edge
eff
Eirka:
Although the Imp is your normal operating condition, you need to design
wire size for an abnormal occurrence (short circuit or other fault). You
do not want the wire to burst in to flame after an unplanned short circuit,
do you? Remember, you may have combiner fuses, but you have no o
olitical statement here, but if the shoe
fits.).
Bill.
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Erika M.
Weliczko
Sent: Friday, April 02, 2010 6:27 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] DC wire sizing
olitical statement here, but if the shoe
fits.).
Bill.
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Erika M.
Weliczko
Sent: Friday, April 02, 2010 6:27 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] DC wire sizing
I believe that the breakers from CBI, Midnite and Outback are hydraulic /
magnetic and may be operated at 100% While the derating applies to all
others that are Thermal / magnetic,
Bob
On Fri, Apr 2, 2010 at 11:14 AM, Kent Osterberg wrote:
> Erika,
>
> You should refer to NEC 690.8 this informa
Yes, they are 100% duty rated. Also, a little-known fact about the CBI
breakers used by Midnite and Outback, gleaned from conversations with
Robin Gudgel: because of this hydraulic/magnetic construction, all are
capable of controlling both AC and DC, even if not listed as both.
f Erika M.
Weliczko
Sent: Friday, April 02, 2010 6:27 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] DC wire sizing
To
my understanding the 156% on PV source and output circuits is related to the
ability of PV to deliver more than rated and be continuous.
Therefore,
the wire has t
Brooks wrote:
From: Bill Brooks
Subject: Re: [RE-wrenches] DC wire sizing
To: er...@repowersolutions.com, "'RE-wrenches'"
Date: Friday, April 2, 2010, 11:14 AM
Erika,
The most correct answer (which is a really funny thing to say) is to use John
Wiles’ “5-step program
And just to be clear, when using these 100% duty rated breakers, you only have
to oversize the cable by 125%, not 156%.
Also, as William mentioned, even correctly sized wiring can have problems; we
just recently had a short circuit that caused quite some damage in a junction
box, and the breake
Ray,
The exception in 690.8(B)(1) reads: Circuits containing an assembly,
together with its overcurrent device(s), that is listed for continuous
operation at 100% of its rating shall be permitted to be utilized at
100% of it rating. The field installed cable used to connect a
breaker is not
Since the topic of AFI's has come up I wonder if anyone has actually tested
one, even an AC one.
From what I've read from some tests on the Mike Holt site for AC breakers is
that they couldn't get them to work at anything less than standard ISC for the
breaker.
thanks,
jay
peltz power
On A
I think the 100% rating exception is an interpretation issue. I consider the
assembly to be defined as the breaker mounted in its listed enclosure.
I agree that the AFIs would add cost, but they might actually offer some
protection too. (possibly one AFI unit could offer protection for multiple
Ray:
It is my analysis that combiner breakers (if present) will protect only
wiring upstream of the combiner -- that is, the individual string
circuits. This protection would happen if there is a fault in one
individual string (in the wiring or the modules) that allows current from
other str
I have seen info from independent tests that convinces me that AFCI's
probably don't work for AC and i hate to think what they would do for DC, if
anything. Besides drive the costs up.
This was a few years ago and maybe they have gotten it together by now.
Anyone remember the original ground fault
I agree that we don't want to create the code first, and try and develop the
product after. On the other hand, if a DC AFI can be developed that could stop
some of the problems I've seen breakers not help, I'm installing them, and
pushing for code requirements.
AC GFIs were gimmicky too at first
Ray,
Considering that we design PV wiring to be efficient with voltage (and
power) loss typically less than 2%, the wire size is nearly irrelevant
to arcing issues. Essentially all the energy available from the PV
array can be dissipated in the dc arc. And since the current is
limited by t
Once I have fulfilled NEC min. requirements, I use a spreadsheet to analyze the
cost of larger wire vs. the cost of power lost. Going under 2% is usually not
worth it, if copper prices are high, and PV cost is low enough (current
market). Sizing for under 2% was good economics a few years back,
Ray,
A 2% wire loss is the generally accepted metric for battery based systems with
relatively low PV voltage input (<150Voc). It's just plain bad design to accept
more than a 1% VD on higher voltage systems. PVs ain't THAT cheap.
Best, Bob-O
On Apr 6, 2010, at 11:44 AM, R Ray Walters wrote:
O
Just run the numbers sometime. Compare the cost difference of #6 vs. #4 wire
say, and then look at how many more watts you're actually saving, then multiply
that additional wattage by the installed cost per watt.
Very simply, once you've satisfied code requirements, there is a point at which
it
Kent,
One of the things to take a look at and to make sure that your
inspector is aware of is the last paragraph of Section 90.4. This was
brought up at the last code meeting to allow new products to come on-
line and to implement new technology into the market. Due to the
timeliness of c
Ray,
Sorry, I'm not buying that argument over a 25+ year design lifespan. Also, -and
perhaps something many folks don't consider- the NEC requires a MAX loss of ≤5%
over the ENTIRE circuit. That means all the way to the mains panel. Best
practices would require no more than 1.5% VD between the i
Subject: Re: [RE-wrenches] DC wire sizing
Ray,
Sorry, I'm not buying that argument over a 25+ year design lifespan. Also, -and
perhaps something many folks don't consider- the NEC requires a MAX loss of ≤5%
over the ENTIRE circuit. That means all the way to the mains panel. Best
pract
ssage-
> From: re-wrenches-boun...@lists.re-wrenches.org
> [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Bob-O Schultze
> Sent: Wednesday, April 07, 2010 1:51 PM
> To: RE-wrenches
> Subject: Re: [RE-wrenches] DC wire sizing
>
> Ray,
> Sorry, I'm not b
tomer explicitly states that he
wants more loss.
Joel Davidson
- Original Message -
From: "Bob-O Schultze"
To: "RE-wrenches"
Sent: Wednesday, April 07, 2010 1:50 PM
Subject: Re: [RE-wrenches] DC wire sizing
Ray,
Sorry, I'm not buying that argument over a 2
inverter and the grid and
> less than 2% overall wire loss unless the customer explicitly states that he
> wants more loss.
> Joel Davidson
>
> - Original Message - From: "Bob-O Schultze"
>
> To: "RE-wrenches"
> Sent: Wednesday, April 07, 20
Schultze
Sent: Wednesday, April 07, 2010 1:51 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] DC wire sizing
Ray,
Sorry, I'm not buying that argument over a 25+ year design lifespan. Also, -and perhaps something many folks don't consider- the NEC requires a MAX loss of ≤5% over the ENTIRE cir
a, CA 94953
Cell: 707-321-2937
Office: 707-789-9537
Fax:707-769-9037
From: Kent Osterberg
To: RE-wrenches
Sent: Wed, April 7, 2010 7:10:58 PM
Subject: Re: [RE-wrenches] DC wire sizing
August,
Thanks for remembering which SolarPro had that article.
expensive.)
Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC
PO Box 657
Petaluma, CA 94953
Cell: 707-321-2937
Office: 707-789-9537
Fax: 707-769-9037
From:
Kent Osterberg
To: RE-wrenches
Sent: Wed, April 7,
2010 7:10:58 PM
Subject: Re:
[RE-wren
Guys,
Is it just me being dense or are none of you folks advocating for higher VD
looking at the savings over time?
If we assume that Kent's wire costs are correct (and even assuming a 33%
mark-up, he's paying WAY, WAY too much for wire) , the difference in delivered
watts between #10 and # 4 wi
Bob-O
Your calculation of the savings proves the point. Going from 10 AWG to
4 AWG costs $2780 today and saves $375 over the next 25 years. Now
think about how much it would cost to put in 91 watts more PV; that'll
save $375 over the next 25 years too.
Granted the published wire prices are
Kent,
In fact, assuming a 33% wire mark-up and the kind of wire pricing that we
Wrenches generally get (I got quotes today), the difference between #10 and #4
is $0.90/ft or $900/M which is how your scenario plays out. You say that just
adding more PV will cover it. I beg to differ. You installi
ject: Re: [RE-wrenches] DC wire sizing
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Bob-O
I just re-opened the spreadsheet that I used to make my example; the
spread sheet was using 330 volts not 350 volts for the voltage drop
calculation. That error doesn't change the example in any material way.
No, I haven't got any 91-watt PV modules these days. But you might get
91 wa
Over the same amount of time a similar investment in PV would save even more
money.
R. Walters
r...@solarray.com
Solar Engineer
On Apr 8, 2010, at 4:28 PM, Bob-O Schultze wrote:
> Guys,
> Is it just me being dense or are none of you folks advocating for higher VD
> looking at the savings ov
IMHO it seems like we're all really on the same page here.. trying to make
the the most out of the the resources we have available to work with..sun
hours, pv, copper, labor, dollars, etc. Job specifics come into play. There are
definitely times when a detailed cost/ benefit analysis is cal
Friends:
Forgive me if this point has already been made:
When designing PV feeders, one typically looks at the Impp of an array for
current specifications. Impp is rarely achieved, however -- only a
handful of days per year and for only a short period of time per
day. This is particularly
Also consider that most people are figuring volt drop at a wire temperature of
167 deg F (75C). That's really hot, and most of the time the wire will be much
cooler, and therefore the volt drop will be less.
(use the fine print note #2, NEC table 8 to adjust down for cooler temperature)
William's
Ray
I think that the point is not the cost, but what is good electrical design!
Voltage Drop in a wire is still undesirable and equates to an unneeded
"heat" load on the wire. Are we advocating that if your water pipe is too
small just increase the pressure so you get the same output you desired
All our economic analysis is based on a 20 to 25 year life.
Safety first, but then good design is to spend the customer's money where it
does the most good.
No matter how big the wire, you will always have losses. It is an exponential
curve that never reaches zero.
It just costs more and more
Has anyone included the extra racking costs to add additional modules used to
compensate for wire loss?
Todd
On Friday, April 9, 2010 10:46am, "R Ray Walters" said:
All our economic analysis is based on a 20 to 25 year life.
Safety first, but then good design is to spend the customer's mon
I figure the PV cost at the total installed cost per watt (module, rack, labor)
R. Walters
r...@solarray.com
Solar Engineer
On Apr 9, 2010, at 12:55 PM, toddc...@finestplanet.com wrote:
> Has anyone included the extra racking costs to add additional modules used to
> compensate for wire loss
Bill,
The NEC is a minimum design design standard, but voltage drops are not
part of the code. The spots where voltage drop is discussed in the NEC
are fine print notes that are not code and are not enforceable as
code. Furthermore those notes were written without any consideration
of the ra
Of course it's not a practical solution, which is why we strived for (but
rarely got) 2% VD on low voltage situations as I said in my first post. The
obvious reply to this post is that your scenario isn't real world anymore. MPPT
controllers fixed that. Or perhaps you advocate that MPPT controll
Bob-O,
I neither subscribe to the notation that cheaper is better nor the
notion that more expensive is better. Adding more wire until 1%, or
any other arbitrary percent loss figure is attained, does not
necessarily make a project better. It will make the project more
efficient to increase t
One small point and well acknowledged on this issue is that we are
starting with a product that only produces at 14-18% [up to19%]
efficiencies to begin with.
A 5%loss is to an average of 16% efficiencies as 31.25% loss is to100%
efficiency.
Till PV modules hit 50-75% efficiency in convers
ches
Sent: Saturday, April 10, 2010 9:22 AM
Subject: [RE-wrenches] DC wire sizing
Here's my challenge to all of you that want to design for 1% or 1.5% voltage
drop all the time:
Take a 50-ft circuit carrying 40 amps at 12 volts, going to a C40 charge
controller, select your wire s
tp://www.wind-sun.com/ForumVB/
..
-
Original Message -
From:
Kent Osterberg
To:
Wrenches
Sent:
Saturday, April 10, 2010 9:22 AM
Subject:
[RE-wrenches] DC wire sizing
Here's my challenge to all of you that want to design for 1% or 1.5%
volta
7-769-9037
From: Bob-O Schultze
To: RE-wrenches
Sent: Sat, April 10, 2010 10:26:56 AM
Subject: Re: [RE-wrenches] DC wire sizing
Of course it's not a practical solution, which is why we strived for (but
rarely got) 2% VD on low voltage situations as I
ox 657
Petaluma, CA 94953
Cell: 707-321-2937
Office: 707-789-9537
Fax: 707-769-9037
From:
Bob-O Schultze
To: RE-wrenches
Sent: Sat, April 10,
2010 10:26:56 AM
Subject: Re:
[RE-wrenches] DC wire sizing
Of course it's not a practical solution, which is why we strived fo
un.com/ForumVB/
..
- Original Message -
From: Kent Osterberg
To: RE-wrenches
Sent: Monday, April 12, 2010 10:51 AM
Subject: Re: [RE-wrenches] DC wire sizing
I know you wouldn't, Warren. Because it is m
ince 1979
>>Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
>>..
>-
>>Original Message -
>>From: Kent Osterberg
>>To: Wrenches
>>Sent: >>Saturday, April 10, 2010 9:22 AM
>>Subject: >>[RE-wrenc
ipant bios:
> www.members.re-wrenches.org
>
>
>
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