[RE-wrenches] Fuse sizing in battery circuits

Drake drake.chamberlin at redwoodalliance.org
Sat Apr 13 12:14:12 PDT 2013


Is it possible that not grounding the DC on an 
inverter could be code compliant?  In the past, 
we were always required to install grounding 
electrode conductors to the DC negative, as 
required for grounding Direct Current systems (250 VIII).

Maybe grounding can be eliminated in a purely AC 
coupled system due to the fact that the system is 
not supplying premise wiring. Maybe the DC can be 
considered as an integral part of the system supplying the AC.

The rules for grounding DC are stated below.

250.162 Direct current Circuits and Systems to Be Grounded
(A) Two-Wire, Direct-Current Systems. A 2-wire, 
dc system supplying premises wiring and operating 
at greater than 50 volts but not greater than 300 volts shall be grounded.
Exception No. 1:  A system equipped with a ground 
detector and supplying only industrial equipment 
in limited areas shall not be required to be grounded.
Exception No. 2:  A rectifier-derived dc system 
supplied from an ac system complying with 250.20 
shall not be required to be grounded.
Exception No. 3:  Direct-current fire alarm 
circuits having a maximum current of 0.030 ampere 
as specified in Article 760, Part III, shall not be required to be grounded.

In a Sunny Island system there is no charge 
control, nothing else in the DC besides the 
battery and battery cables.  Does not grounding 
the negative really meet code requirements in the 
US ? Are the inverter cables not considered to be premise wiring?

Thanks,

Drake


  At 03:56 PM 4/10/2013, you wrote:
>Content-Class: urn:content-classes:message
>Content-Language: en-US
>Content-Type: multipart/alternative;
>         boundary="_000_B448FC9E37458B469E77EA0BB954AD4702BD99AC6Emailbox01_"
>
>August:
>
>The SI can run with an ungrounded battery or a grounded battery.
>With the internal breaker it is set up for a negative ground battery.
>I believe the manual says ground at the battery terminal.
>If you chose to go ungrounded you will need to 
>have an OCPD in both battery + and battery – (all ungrounded conductors).
>
>I am pretty sure the SI is not internally bonded to ground.
>This is normal in the rest of the world.
>Mine are running with an ungrounded battery and 
>there isolation between battery and ground.
>
>Best Regards,
>
>John Berdner
>General Manager, North America
>
>SolarEdge Technologies, Inc.
>3347 Gateway Boulevard, Fremont CA 94538 
>USA  (*Please note of our new address.)
>T: 510.498.3200, X 747
>M: 530.277.4894
>
>From: re-wrenches-bounces at lists.re-wrenches.org 
>[mailto: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: 
><mailto:re-wrenches-bounces at lists.re-wrenches.org>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>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>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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