Thanks for the Clarification Bill, I may forward your comments to the
AHJ at some point. The system is proposed to be located in the 4 car
garage, so there will be cars filled with gasoline in there as well.
I always keep my battery cable runs short as possible, in this case the
bank will be long and skinny, but the positives can be located at the
end near the inverters. The negative (grounded conductor) will have the
long run through the battery enclosure. Only the 3rd inverter would be
more than 5 ft from the battery enclosure. I am considering a battery
combiner box with breakers for each string (only 2 strings) to meet
690.71(H)
As others have pointed out, killing the AC output of the inverters is
much easier to accomplish remotely. Locking the Birdhouse would prevent
unauthorized disconnection of critical loads, but unfortunately the
Birdhouse does not have lockable cover, so that is still a very real
concern for the owners. As you pointed out, the real danger of the
backup system is the batteries themselves, I spoke with firefighters
this week, and they have to go into HAZMAT mode when they start dealing
with a large battery bank. So as you mentioned, the short run of 48 vdc
is not what they are concerned with.
My main goal at this point is not to get red tagged and have to retrofit
a bunch of expensive, special order gear later. Our motto: "Do it right
the first time" is easy to say, but can be hard to live up to.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 8/26/2015 10:19 PM, [email protected] wrote:
Ray,
Do you have a massive battery bank and 3, 8kW inverters inside the house? Is
this in a garage or power shed. If it is a power shed, then 690.12 is not
intended to relate to the power shed. That will be clarified in the 2017
NEC.
The area for discussion is what constitutes the length of battery cables.
690.71 has restrictions on where overcurrent protection needs to be for
circuits longer than 5'. Do people really follow that religiously? This
would be a discussion that really needs to happen with the AHJ. My basic
view is that if I have a 4' run from a battery box to my inverters (even
though one lead may be 10' long), many would call that a 4' run. That is
what is exposed from a fire fighter point of view. Remember the battery is
potentially a massive bomb in a fire, so 48V conductors are the least of a
fire fighter's concern.
Bottom line is how to make it easy for a firefighter to kill the vast
majority of wires in a building. A backup system simply reenergizes
everything. Cutting off the dc from the array and the ac out of the
inverters solves the problem--keep the battery as close as possible and
don't worry about trying to turn off the battery circuit to the inverter.
Bill.
-----Original Message-----
From: RE-wrenches [mailto:[email protected]] On
Behalf Of Ray Walters
Sent: Wednesday, August 26, 2015 12:40 PM
To: RE-wrenches <[email protected]>
Subject: [RE-wrenches] Rapid Shutdown Battery Systems
Hi Wrenches;
I have an upcoming project to be inspected, ,and having spent too much time
on off grid and out of country work, I'm now playing catch up with the new
690.12 and 690.71(H) requirements.
The proposed GTB system is 3 Radians with a ground mounted 18kW array and
large HUP battery bank. I just read a Bill Brooks article that basically
says that Rapid Shutdown not only applies to ground mounted arrays that come
into buildings, but also applies to battery cables if longer than 5 ft.
There are 690.12 compliant combiners from Midnite that work with their
Birdhouse system, so I think I've got a handle on the array requirements
(more or less).
What is stumping me is how to feed three 8kW inverters from a large battery,
and install auto disconnect breakers within 5 ft.
1) the disconnect has to be large enough, Midnite only makes a 250 amp
remote trip breaker, so I'd have to parallel 3 of these?
2) 690.71(H)3 says the breaker can't be in the battery enclosure, which is
tricky since the enclosure is 160" long from one end to the other with 2
parallel strings.
3) I'm having trouble even finding an enclosure for 3 large DC breakers
(Flex 1000 is the only thing I know of) and to get the enclosure close
enough is an issue too.
I just got off the phone with Tech support at Outback and they don't seem to
have any Rapid Shutdown gear ready.
Are inspectors actually requiring this yet, or because of the lack of
available UL listed products, can we take a pass on at least some of the
requirements? Another strategy the Outback tech thought of is to put all
the equipment into a shipping container and then its not in or on a
"building", and 690.12 doesn't apply.
--
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
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