six motions of the hand [RE-wrenches]
mlafferty at universalenergies.com
mlafferty at universalenergies.com
Wed Dec 24 19:40:29 PST 2003
Christopher F Wrote:
> My understanding of the NEC code is that the DC and AC
> systems are considered as seperate sources of power.
> Therefore - you get 6 "motions of the hand" for each of
> the systems.
All:
Thanks for the kind words, Chris, first of all. Don't worry about
getting us all an "FX X-Mas Present"... Go for a New Year's Present
instead!
Never one to split hairs on verbiage (who, me???), I will offer a
repeated "Caution" surrounding this topic when dealing with Inspectors,
Code, and Building Departments.
"This is a slippery slope....."
We may all know what we mean when we say "source of power" and
"system"... We may know that they are functionally interchangeable when
used for this conversation.... The NEC DOES NOT!....
A source of power does not necessarily equal a "system" and vice versa.
The NEC does not use the terms interchangeably.
I am from a line of thinking that "non-backup pure grid-tied PV"
applicationers (is that a word?) should erase the term "separate system"
from their vocabulary.... We are "Interactive"... (Stays away from all
the hold-down breaker and confused grounding stuff that way!)
In all fairness, one should not expect to have their cake and eat it
too, even if it is X-mas Eve... In which case, I would expect it to be
pie instead of cake, but in any case, Season's Greetings to all,
regardless of the dessert selected... Just hope everybody got some, no
matter what their beliefs may be... I chose beer, for the record.... LOL
Back to the topic at hand... If you choose to use the "separate system"
approach, be prepared to be held to other requirements of the Code.
If you elect to go with the "Interactive" (Read this as "not separately
derived system") approach, be prepared to meet the related Code
sections.
Due to the diversity of possible system configurations, there isn't a
"one size fits all" answer that I know of... Other implications come
into play, too. Like your local Inspectors and Building Departments...
Your relationship with them... I'll leave Unions out of it this time...
The variation in your applications, Etc.
Keeping it short for all of our sakes,
Two Palms, A Hammock, & Winning Lotto Tickets for All!
Matt Lafferty
mlafferty at universalenergies.com
(916) 422-9772 Office
(916) 914-2247 Fax
(916) 628-7694 Cell
www.universalenergies.com
-----Original Message-----
From: Christopher Freitas --- OutBack Power
[mailto:cfreitas at outbackpower.com]
Sent: Wednesday, December 24, 2003 12:10 PM
To: RE-wrenches at topica.com
Subject: RE: six motions of the hand [RE-wrenches]
Matt made many good points on handling the inspector - I agree and have
used many of them myself...
The term "six motions of the hand" is used more with
commercial/industrial applications - but most inspectors understand the
idea. The code also has some flexibility on how it is to be applied.
My understanding of the NEC code is that the DC and AC systems are
considered as seperate sources of power. Therefore - you get 6 "motions
of the hand" for each of the systems. This is in addition to the
disconnect for the utility service to any non-backed up loads.
Multiple breakers which are "handle tied" together are considered to be
one switch - even when they are not paralleled together as a single
device. This can reduce the number of "motions" involved. I even have
had inspectors allow one hand motion to turn off several breakers
located all together which were not handle tied together. Its their
call after all.
The requirement for shutting down the system in six motions is not to
operate every disconnect or breaker involved - but it is to stop the
flow of power quickly and easily. So the PV array can be disabled by
throwing the PV array side breaker or the battery side breaker for the
controller - both are not required to be operated.
Similarly - the AC output breakers on the inverter should not be
required to be turned off if the AC input breakers and DC battery
breakers are operated - along with the PV array.
I've also been involved with jobs where providing an emergency OFF
switch was viewed as being more important - mostly due to the access
issues for the disconnects. Many newer inverters (like the OutBack FX
series) has terminals to allow connection of just this type of switch
remotely located.
Obviously - this all can get messy - but I have found that providing the
inspector with a logical, well documented presentation ahead of time is
very useful in getting him to be more comfortable - it also gives him
something to put in his file to later reference if he gets called on it.
I usually do not put these types of documents on letterhead - leaving
it up to the reviewer to decide who actually did the work creating it.
This can be helpful to the inspector back at his office when he needs to
document the job and the work he has completed...
Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030
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