[RE-wrenches] 2 PV utility interconnect disconnects?
Matt Lafferty
gilligan06 at gmail.com
Wed Feb 25 11:57:15 PST 2009
Joel,
You are describing an NEC compliant configuration. Independent of the
"utility". Determining whether or not the interpretation/requirement is
excessive will require some additional information and will vary by project.
For instance: Per the NEC, a Supply Side connection (what we lovingly refer
to as "line-side") has several inherent requirements, besides the actual
physical connection method. These requirements will determine what the
appropriate configuration would be.
The short list includes:
* Location of connection point (For net-metered installs: Between the
Revenue Meter and the Customer Service disconnect)
* Length of tap conductors. (< 10' in most cases)
* Location of first disconnect device. (Accessible, grouped, etc.)
* Location and setting of first overcurrent protection device. (May or may
not be integral to the disconnect device)
It is critical to understand that a service disconnect does not necessarily
include overcurrent protection. See below for some examples. A lot of guys
use unfused safety switches for their load-side connections. A load-side
connection (breaker) has overcurrent protection ahead of the "disconnect".
Remember that, what we call the "disconnect" is/was a utility requirement.
>From an NEC perspective, the breaker serves as a disconnect and overcurrent
protection device.
Many guys miss a fundamental difference between the load-side and
supply-side cases... The location of the overcurrent protection device
relative the service disconnect. If you use a fused safety-switch/disconnect
within the appropriate proximity, then you have the "code" side covered.
Once you have covered the NEC aspects, then you get down to the generator
requirements of the ESP utility. They may have collective bargaining
agreements or other requirements that say "visible, lockable, accessible to
utility, not accessible to customer". The last clause is a sticky one.
Basically, it has been interpreted as: Customer is prohibited from operating
the switch or replacing fuses. If you go back through the older
interconnection agreements, this is, in fact, the case. The "utility"
disconnect is to be operated and accessed by utility personnel ONLY!. Read
'em. It's in there. The way utilities have interpreted and "enforced" or
"not enforced" the letter of the interconnection agreement (it's really a
contract) has varied. Often by local service center. One place requires that
a utility lock be installed on the disconnect with the handle "up" so the
customer cannot operate it. The next town over, in the same utility, they
don't bother. That kind of stuff. Besides the innocent differences, they
could also just have hard-headed pricks in the engineering department of
their distribution services division. Modern inverters are NOT the same
thing as a spinning turbine, but some of the legacy perspectives are that a
"generator is a generator" and that "a single standard is easier to
maintain". Think about this: If you are an old-time utility engineer, why in
the world would you want to draft up and implement a separate standard for
inverter-based generation when you only have 10 years to go until
retirement? If you can spend your energy for the next 10 years having
another meeting and protesting and procrastinating and walking from one side
of the campus to the other and doing safety inspections on office chairs,
why not? Oh, yeah. I know those guys. They wrap themselves in the almighty
"safety and reliability" flag. Their seniority in the organization gives
them influence that, frankly, might not be justified. Nevertheless, it is a
fact. In some cases, retirement is the only solution. Some AHJs go in this
cupboard, too.
Back to some real-world examples that should help drive the principle home.
The "misunderstanding" some installers have.
In my travels, I have found a few, probably less than 10, that didn't have
OCP at all. I've also found a location that has a couple of relatively large
systems, with multiple inverters on each, that didn't have OCP until the
inverter branch circuit breakers in the IDPs (Inverter Distribution
Panel)located on the roof! The latter is on a multi-story, modern office
building, and has 2 separate interconnections set up the same way. One of
the systems is rated at ~75A max and the other is ~125A max. 3-Phase. To be
clear, we are talking about 2 independent generation circuits that are
(still) connected to the supply-side of 800A & 1200A services without OCP.
To be clear, the shortest of the two circuits is ~130' one-way. To be clear,
this was installed by an electrical contractor.
To be clear, all of these examples were signed off by the local AHJ and by
the ESP utility. That doesn't make it right! Some of them have been
corrected now and some haven't.
The tragic thing is that, from a purely utility lineperson's perspective,
the unfused disconnect is just fine! He or she can slap the handle, isolate
the generator, slap a lock on the handle, and go sit in the truck to wait
for the line-crew to say "all clear".
The NEC and the NESC and the collective bargaining agreements aren't, shall
we say, harmoniously aligned.
So, to answer your question Joel, the specifics of an individual project
must be considered in order to determine whether or not the requirements are
excessive.
A long time ago, in a life far away, I dealt with the standardization issues
at SMUD. I was able to get the meter shop to accept a set of standards about
meter and disconnect locations based on the application. Doing the heavy
lifting of writing it up and doing all the drawings basically took the
"power to say no" away from distribution services and meter shop. Back then,
there was an all out war over whether or not PV was gonna survive.
Distribution services was doing everything they could to squash it, and the
meter shop basically just had heartburn over not having a clear standard and
procedure they could expect to be followed for solar installations. (Lots of
"pre-Matt" history in all that...) I did a 1-hour presentation to the Meter
Shop, including field meter techs. I also did a 1/2 day training with my
contractors and SMUD's Solar Specialists... Everybody got a copy in a binder
to put in their trucks. They were very grateful and the standard became a
good quality control measure. Whenever one of the SMUD Solar Specialists or
Contractors weren't following the approved standards, I didn't have to be
the babysitter any more. Everybody had the same set of rules. If the
interconnection piece wasn't right, the Meter Shop didn't hook it up and the
contractor didn't get paid. No more, "I followed the plans and they were
wrong". No more, "don't tell Matt we're gonna do it this way". Everybody had
to buck up.
No more trying to install solar on houses and outbuildings that didn't have
suitable electrical service provisions. The customer had to upgrade BEFORE
the solar crews came! (Quality Control step 1)
The plans had to be right or the contractor didn't install it. (Quality
Control step 2)
The Meter Shop didn't change out the revenue meter or set the generation
meter if any part of the job wasn't up to snuff. (Quality Control step 3)
Added Benefit: Distribution services had to shut up. The Meter Shop became a
positive ally instead of not having a lot of good things to say.
It was SMUD specific, related to the packaged PV systems we were installing
at the time. (SMA SWR-2500's with 20 ea. KC-120's). Even though the standard
was limited to residential systems having 2 or less Sunny Boy 2500's, it
takes 18 drawings and individual descriptions to cover. When I wrote it, I
kept an eye toward making it in a template format so it could be useful
elsewhere in the future. For instance, a generic inverter could be
represented and the amperage of the breakers & disconnects and fuses
wouldn't need to be called out.
I uploaded a PDF of this to the Wrench FTP server and asked Michael to move
it to the public side. Let me know off list if you don't see it here:
ftp://ftp.re-wrenches.org/pub/
I still have all the original dwg's and wmf's and word document... If you
have a good reason for wanting any of that, let me know. I won't release
them in that format without taking my name and SMUD logos off them for
<hopefully> obvious reasons. Nothing personal, mind ya. After a soft-scrub,
I'd be happy to pass it along for good purposes.
Happy standardizing!
Matt Lafferty
-----Original Message-----
PV installers in the LADWP area are being told to put a disconnect switch
and circuit breaker between the revenue meter and the customer's service
panel if we use a line-side tap. Do any other electric utilities require PV
system disconnect switch and a 2nd additional disconnect switch on a PV
system with a line-side tap?
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