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
<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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