[RE-wrenches] Fuse sizing in battery circuits
August Goers
august at luminalt.com
Wed Apr 10 14:13:27 PDT 2013
Steve,
So if we wanted to ground the negative would we literally run a ground wire
to one of the battery terminals? Is there anything in the NEC that governs
this? What are the deciding factors when deciding to ground the negative or
not?
As a separate note, I've noticed that the negative battery terminals
measure 0 volts to ground on a Sunny Island setup once everything is
connected without any extra grounding added. I thought that there must be
some reference to ground happening in the Sunny Island but apparently I'm
wrong.
Thanks, August
*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Steve Jefferson
*Sent:* Wednesday, April 10, 2013 9:56 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits
If the Batt negative is not bonded to ground, then yes SMA recommends
fusing both Positive and Negative.
Also, the negative is not bonded to ground internally in the Sunny Island.
SMA America, LLC
Steve Jefferson
*Supervisor, Service Line*
6020 West Oaks Blvd, Suite 300
Rocklin, CA 95765 - 3714
U.S.A.
Tel: +1 916 625 0870
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Email: steve.jefferson at sma-america.com
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*From:* re-wrenches-bounces at lists.re-wrenches.org [
mailto:re-wrenches-bounces at lists.re-wrenches.org<re-wrenches-bounces at lists.re-wrenches.org>]
*On Behalf Of *August Goers
*Sent:* Wednesday, April 10, 2013 9:45 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits
Hi All -
As a slightly separate topic, should we fuse both the positive and negative
battery lines with an SMA Sunny Island? I believe that the negative is
grounded so should not be fused but I've heard conflicting stories from
tech support.
Thanks,
August
*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Drake
*Sent:* Wednesday, April 10, 2013 5:52 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits
boB,
SMA does recommend protecting Sunny Islands with a fuse on the battery,
even though the breakers on the units are rated for 10,000 Amps. Are the
SI breakers inferior others you have mentioned?
Thanks,
Drake
At 12:14 AM 4/10/2013, you wrote:
After 100's of thousands of inverters having been shipped in the last many
years
and thousands of inverters broken and shorting the battery terminals, there
has
never been (to our knowledge) one breaker that has not tripped.
The Midnite site lists the AIC rating of all our breakers I believe.
The Carling F series of Magnetic-Hydraulic breakers poop sheet is here...
http://www.carlingtech.com/sites/default/files/documents/F-Series_Details_%26_COS_0.pdf
I guess there isn't a graph of AIC vs. voltage on their F series web page
but we remember
them showing us figures or a graph that says those breakers have an AIC of
more than
100,000 amps at 48 volts. We'll try to find that info or you may be able
to get that
from Carling.
I have, many times, directly connected these breakers across good L-16
battery strings
to demonstrate the left-hand rule to people where the 4/0 cable jumps apart
or towards each
other when very high current passes through those wires when they are near
each other.
It always trips. Never tried it at anything above a 48V battery banks IIRC.
Robin would like to mention that anyone that wants to use T-Classc
fuses.... Welcome back to the 1990's
boB
On 4/9/2013 1:23 PM, Ray Walters wrote:
Hey Bob;
Can you share that AIC vs Voltage chart?
Thanks,
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 4/9/2013 1:46 PM, boB wrote:
Those 250 amp and 175 amp breakers we have used for many many years now
have an AIC of 50,000 amps at 125 volts and if you look at the curve, at 48
volts
they are around 100,000 amps. I think that this information is on the label
of the breaker.
How many problems have you had with the Carlings or any other type of
those large breakers ?
boB
On 4/9/2013 10:40 AM, Michael Welch wrote:
If anyone would like an Acrobat version of this article, you can find it
here:
ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf
William Dorsett wrote at 07:00 AM 4/9/2013:
This topic comes up often enough that we ought to mention a yellowed
article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas
wrote *Overcurrent
Protection for Battery-Powered Systems *where he describes experiments he
did back when he was with Ananda. He put a 2000 A Big Switch to initiate a
short (4/0 cable) between the terminals on a set of four golf cart
batteries (2 strings @ 12V). In series, he put in a 500A Shunt so he could
measure current passing and various fuses and breakers. “For comparison, we
decided to directly short the battery…the meter read 6960 amps peak current
(three seconds) …during each test the 4/0 cable lifted off the ground 4
inches into the air by the forces generated by the extremely high
current..” They videoed the 250 A ANN buss fuses arc and smoke; the 200A
Heinemann Series AM breakers (paralleled ones that maybe Roy mentioned)
went 3 seconds without breaking and the video showed a flash and blue
smoke.
175A ITE breaker with 42,000 AIC “simply tripped…but still allowed a peak
current of 2960 amps
200A Class T Littlefuse “opened promptly with no external signs of
stress…1920 amps peak current”
Christopher’s recommendations:
“Every AE system must have overcurrent protection able to interrupt the
maximum current available from the batteries. For most systems, the main
protection should use current limiting high AIC fuses, such as a Class T or
Class R. A disconnect switch which allows the fuse to be safely changed
should be included. A lower cost alternative is to mount the fuse in a fuse
holder without a disconnect. Although the fuse would always be electrically
hot, it normally would not be changed during the life of the system. The
fuse holder should be mounted outside the battery enclosure. Fuses should
not be bolted directly onto the battery terminal, as they are not designed
to handle the physical stresses that can occur without the protection of a
fuse holder.
Fuses which have exposed elements, such as ANN fuses, should not be used
because they are not current limiting and have only 2500 amps AIC. They
also may be a significant hazard when installed near batteries.
High AIC breakers, like the Heinemann Series CF (25,000 Amps AIC @ 65VDC)
can provide overcurrent protection for individual items. They cannot be
used to protect lower AIC breakers. This eliminates their use as a main
disconnect in most systems.
Low AIC breakers, like the Heinemann Series AM (5000A AIC @65 VDC) or the
Square-D QO (5000A @ 125 VDC) can be used in load distribution centers and
components, but must be protected by a current limiting fuse. Using low-AIC
breakers alone will not provide sufficient protection with a battery system
and may be a significant hazard during short circuit situations.”
It won’t pull up anymore on HP’s article search but probably Michael has a
copy he could post for those interested.*
*
Bill Dorsett
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