[RE-wrenches] MC4 Y Connectors

[penobscotsolar at midmaine.com]

My whole point is that this method is only good when you are paralleling
two strings, per breaker/fuse, no more. The "Y's" only combine two
strings. That allows an installer to cut in half the amount of
fusible/breakered strings in an installation. If you have 10 strings of
three panels you can parallel two sets of three panel strings five times.
This is an efficient design approach saving both installer time and the
customer money while fully protecting the system. It also makes wire
management much more aesthetically pleasing.

Daryl



> My take: if you have no more than two strings feeding your inverter,
> this is NEC compliant. If you have a ten-string array and you're
> planning to use a 5-fuse combiner, you're probably out of luck.
>
> Reason 1:
> For a typical 240W-ish module your Isc is around 8.5A. 8.5 x 1.56 =
> 13.3A. If you have two strings in parallel you would need to put a 30A
> fuse on the paralleled output-- according to the spreadsheet in SolarPro
> 4.6, the biggest fuse allowed for any cSi module is 20A, so this would
> only work with modules that have an Isc < 6.4A.
>
> Reason 2:
> If you have a fault in a string, you could have (Isc x 1.25) current
> from each parallel string sharing the fuse + (fuse value) 20A from the
> fuse flowing into that fault. With just one string per fuse, your fuse
> protects your module. With more than one string per fuse, the extra
> current contribution from those strings bypasses the fuse protection.
>
> I'm not seeing how this product is useful for cSi systems that have more
> than two strings. Maybe for some thin-films with low currents, a small
> fuse on their output, and a big max series fuse rating. If a module had
> a 30A fuse allowed and an Isc of 3.2A, you could do a 15A fuse on up to
> 3 strings.
>
> More info is in John Wiles's "PV and the NEC" guide, Appendix J.
>
>
> On 2012/3/9 10:33, Richard L Ratico wrote:
>> Can someone please explain why this is a bad practice? My understanding
>> is
>> the fuse will still prevent backfeeding a fault by more than one
>> additional
>> string,
>> the one paired by the Y connector. All the other strings are downstream
>> of
>> the fuse.
>>
>> Dick Ratico
>>
>> --- You wrote:
>>> Wrenchers,
>>> Has anyone used MC4 Y Connectors to combine strings?  This website
>>> claims
>>> that they are TUV Certified but does not list the manufacturer.  Seems
>>> like best practice to fuse each string but wanted to see what others
>>> think
>>> about this product and the idea of fusing every two strings instead of
>>> each individual string.
>>>
>>> http://www.solarpenny.com/MC4-Y-Connectors-609-4431.htm
>>>
>>> Al Frishman
>>> AeonSolar
>> --- end of quote ---
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