While Brian T. is correct that fusing is not required for string-to-string overcurrent protection with two strings into two channels, there is another reason to require fusing.
Transformerless inverters like Fronius Primo have no transformer to provide AC-DC isolation, so a ground fault can allow excessive AC current from AC neutral to enter the DC side and fry inverter components. Transformerless inverters need fuses on both DC
positive and DC negative legs to protect the inverter in case of ground
fault.
This is why both DC+ and DC- are switched and PV wire is
required for DC connections-- to protect
the inverters, not just the PV modules.
This is also why SMA, for example, no longer has any fuses in their disconnect switches but requires a separate fused DC combiner box with fuses for both positive and negative circuits.
I have had inverter damage with another inverter brand that only had fuses for the DC+. They now provide fuses on both legs.
Don Barch
Energy Solar
Date: Wed, 27 Jan 2016 17:31:22 -0800
From: Brian Teitelbaum <bteitelb...@aeesolar.com>
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>
Subject: Re: [RE-wrenches] fusing requirement for 4 strings run to a
Inverter with 2 MPPT's
Message-ID: <7b344022a97655195ced29e564a31...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Al,
As long as you only have a max of two strings going into each of the
separate MPPT channels, no string fusing is needed. So with four strings,
two on each MPPT input channel in the inverter, no string fusing is needed.
This is one of the big advantages to having multiple MPPT channels in GT
inverters.
No need to run separate conduits either. All four PV string circuits can be
run in a single conduit, as long as the conduit is properly sized for wire
fill, of course.
Brian Teitelbaum
AEE Solar
*From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On
Behalf Of *Allen Frishman
*Sent:* Wednesday, January 27, 2016 6:12 AM
*To:* re-wrenches@lists.re-wrenches.org
*Subject:* [RE-wrenches] fusing requirement for 4 strings run to a Inverter
with 2 MPPT's
Wrenchers,
What is the requirement for fusing 2 strings per MPPT? Specifically for
an inverter like the Fronius Primo that has no integrated fuses. If you
run 2 strings to each MPPT do you need to fuse each string? In this case
there is a total of 4 strings which would need to be fused if using a
single mppt.
If the home runs are run in separate conduits from the array to limit the
strings in the conduit to 2 per you still have all 4 strings together in
the inverter.
All thoughts and feedback are appreciated.
*Al Frishman*
AeonSolar
*(917) 699-6641 <%28917%29%20699-6641> - cell*
*(888) 460-2867 <%28888%29%20460-2867>*
*www.aeonsolar.com <http://www.aeonsolar.com/>*
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