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: [email protected]
[mailto:[email protected]] 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:[email protected]>[email protected]
[mailto:[email protected]] 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
Christophers 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 wont pull up anymore on HPs article search
but probably Michael has a copy he could post for those interested.
Bill Dorsett
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