[RE-wrenches] Fuse sizing in battery circuits

Wed Apr 10 12:56:58 PDT 2013

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: re-wrenches-bounces at lists.re-wrenches.org<mailto:re-wrenches-bounces at lists.re-wrenches.org> [mailto: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

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

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