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-boun...@lists.re-wrenches.org [mailto: re-wrenches-boun...@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 Fax: +1 916 624-2445 Service Line +1 877 697 6283 (Toll Free) Email: steve.jeffer...@sma-america.com www.SMA-America.com <http://www.sma-america.com/> This email and any attachments thereto may contain SMA America, LLC confidential, privileged and private material for the sole use of the intended recipient. Any review, copying, or distribution of this email (or any attachments thereto) by others is strictly prohibited. If you are not the intended recipient, please contact the sender immediately and permanently delete the original and any copies of this email and any attachments thereto. Thank you. *From:* re-wrenches-boun...@lists.re-wrenches.org [ mailto:re-wrenches-boun...@lists.re-wrenches.org<re-wrenches-boun...@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-boun...@lists.re-wrenches.org [mailto: re-wrenches-boun...@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 _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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