FW: system expansion [RE-wrenches]

John Berdner jberdner at sma-america.com
Fri Aug 24 13:09:09 PDT 2007


Sky/Wrenches:
 
I can only speak for my own experience with UL testing of plastic
parts.
First you put thermo couples on the part that is being tested.
You then run the device at the maximum rating and at the specified
ambient temperature.
For most components you find today the temperature of the test was
25C.
You are allowed to scale the temperatures up to an ambient of 40C, i.e.
just add 15C to the 25C data.
Above 40C you have to run the test at the specified ambient
temperature, i.e. you can't just add 20C to 25C data to get 45C
ratings.
UL then looks up the characteristics of the particular plastic for
deformation and sees if you pass of fail.
 
I am not saying I buy the argument of the plastics deforming before the
breakers open.  I believe what the SquareD guy was saying is that they
had not tested their panels with the added thermal loading of a bunch of
additional PV breakers in the panel.  At 120% he was not really
concerned but he was concerned if we changed to code to allow higher
levels of PV in the panel.  The concern the 120% rule is trying to
address is a situation where the PV breaker is installed at the top of
the bus bar just under the main lugs.  Using a 200 Amp panel with an
additional 100 Amps of PV breakers as an example: Someone theoretically
could put 300 Amps of load breakers in the panel and no over current
devices would trip even though the bus bar could be at 150% of it's
design current.  Frankly, I do not buy this argument either since you
would inevitably end up with nuisance tripping of the main breaker on
cloudy days, in the morning, at night, etc.
 
As you pointed out, there is NO ISSUE of bus bar rating if you put the
PV breakers at the bottom of the bus bar.  As long as the total of the
PV is less than the bus bar rating, you can not create a scenario where
the bus can be overloaded.  This was the position we (the PV industry)
were arguing and trying to get into the 2008 Code.  The sub panel
manufacturers argued against this and won.  Hmmm...do load center
manufacturers make more money by selling a 400 Amp panel where a 200 Amp
panel would be adequate ?
 
I personally would like to see another Code approved alternative in the
form of a labeling requirement for panels with a mix of generation and
load breakers.  If the panel has a mixture of load and generation
breakers then it should be labeled as such and have a Code required
label that says the total of all the generation breakers can not exceed
the rating of the bus bar AND the total of all the load breakers cannot
exceed the rating of the bus bar.  While there is no perfect solution at
least under the labeling scenario we could use panels up to their full
rating instead of having to double the size of the panel for nothing.  
 
I agree that PV systems need to be safe but >> IMHO <<  our
Code/UL/IEEE requirements are driving costs up to cover hypothetical
situations that are extremely unlikely.   I whole heartedly agree with
you that we need to have ore balance between risk and cost or we are
never going to get costs down. Installation costs in the US are roughly
double those in Europe or Japan and both of those places have high cost
labor just like we do. Sometimes it seems like some of the guys on the
regulatory committees are trying to use regulations to keep stupid
people from stupid things.  As a good friend of mine is fond of saying
"All the regulations in the world won't stop someone from putting gas in
his diesel truck". 
 
The first meeting for the 2011 Code will be at Solar Power 2007.  If
people want to be involved in the process get in touch with John Wiles
and tell him you want to participate.  I can tell you it is pretty mind
numbing sometimes but occasionally we do get rid of bad requirements or
add some new ones that make sense.  In the past I feel the installers
have been under represented and I, for one, would love to see more input
with real world perspective. 
 
Best Regards,
 
John Berdner
 
 
>>> sky at ecologicalsystems.biz 8/22/2007 10:59:11 AM >>>


"Square D was saying that the plastics that support the bus bars can
get

too hot and deform in this situation especially if the panel is
exposed

to direct sun.

He did not go so far to say this would create a hazard but he did say

this was something they do not test for so it potentially could be an

issue." 



The lack of testing on the plastic supports does not even begin to
make

sense to me. I find the concept ridiculous. Every material in a panel

has to have been tested (to failure) and rated at some point in the

manufacturing and component selection process. The actual temperature
at

which the plastic supports melt or lose their integrity must be

documented by the manufacturer, otherwise how would they get it listed

for use in a temperature sensitive environment. 



Regardless this concern remains a non issue because of the thermal

nature of the breakers which will result in breakers tripping off
before

heat build up becomes an actual hazard to the integrity of the bus or

the plastic standoffs. (please correct me with manufacturers data if I

am mistaken)



"The total thermal loading of the panel is potentially 480 Amps worth
of

breakers (200 main, 240 load, 40 PV)."



As for this point, so what? Is someone trying to imply that the

resistive loads of breakers feeding loads is so high that it will
result

in the panel reaching a dangerous temperature before the thermal
nature

of the breakers causes them to trip? In this scenario the bus still
only

sees 240 amps. And as long as the solar fed breaker is at the opposite

end of the bus from the main breaker (something I've always
encouraged)

no point on the bus will ever see more than 200amps, even if the solar

fed breaker was a 200amp breaker instead of the 40amp in this example.



These points that are being raised as reasons to limit the allowable

size of a solar fed breaker to anything less than the tab rating of
the

panel are ridiculous. 



In any scenario that I can think of the solar breaker either offsets
the

power being fed from the utility fed breaker or breakers start
tripping

and it becomes very apparent very quickly that the panel needs to be

upgraded. (let me know if I'm missing something)



I am very concerned about standards raisers adding costs to systems
for

ridiculous reasons. This industry really needs to focus more on how to

reduce costs so that everyone can obtain a system.



If we applied the same philosophy to the wiring in our homes as we do
to

solar we would all be living in padded cells. Our TV's would be hard

wired to an inaccessible power supply and the wires would be encased
in

conduit so that children couldn't bite through the wires when we
aren't

looking or stick their fingers in the outlets. Every time we decided
to

move the TV or replace it a skilled professional would have to come
out

and do it for us. And the only people with electricity would be the

wealthiest 5 percent of society because the cost would be so high that

no one else could afford it.



There must be a happy middle ground between safety and affordability.

People use gas in their homes in spite of the "reasonable" risks
associated with

carbon monoxide poisoning and the fact that nearly 100,000 people in

this country are negatively affected by its use annually many actually
killed. Solar isn't at all like that.



Plug and Play should be our shining goal. Allowing inverters to be

simply plugged into an exterior or interior outlet is something that
we

should be pushing for (European countries already allow this). Getting

the tab rating versus bus rating issue addressed is worth pushing for
now. 



At this point it may be time to get some materials engineers from some

of the bigger panel manufacturers like square d, siemens, cutler
hammer

etc.. to weigh in on this issue.



My 2 cents,

Sky Sims

Ecological Systems

www.ecologicalsystems.biz 

ph)732-462-3858 fax)732-462-3962





--
[Non-text portions of this message have been removed]


- - - -
Hosted by Home Power magazine

To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael_welch at sbcglobal.net

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------





More information about the RE-wrenches mailing list