[RE-wrenches] fusing requirement for 4 strings run to a Inverter with 2 MPPT's

[Jay]

Hi Dan

Can you provide any documentation on this?  

Thanks Jay
Peltz power. 


Sent from my iPhone

> On Jan 28, 2016, at 8:52 PM, <don at energysolarnow.com> <don at energysolarnow.com> wrote:
> 
> 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 <bteitelbaum at aeesolar.com>
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> Subject: Re: [RE-wrenches] fusing requirement for 4 strings run to a
> Inverter with 2 MPPT's
> Message-ID: <7b344022a97655195ced29e564a31c54 at 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-bounces at lists.re-wrenches.org] *On
> Behalf Of *Allen Frishman
> *Sent:* Wednesday, January 27, 2016 6:12 AM
> *To:* re-wrenches at 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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