[RE-wrenches] Fuse sizing in battery circuits

Wed Apr 10 05:52:05 PDT 2013

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>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
>>303 505-8760On 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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