[RE-wrenches] Fuse sizing in battery circuits

[Ray Walters]

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
>>
>> <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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