Do installations with transformerless inverters require combiner boxes with OCPD?

Hello,

To my knowledge in installations with only 1 or 2 series strings a combiner box is generally unnecessary as the strings can be run directly into the inverter inputs. However, I've been told that installations using a transformerless inverter always require a separate combiner both with OCPD. Is this correct?

Doug

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Doug,

All transformerless inverters are slightly different, but here's an example:Kaco XP10 Transformerless

2 MPPT Input circuits with four strings total (in this example).
Each input circuit has two strings and each string is rated for the same short circuit current (module Isc rating).
No OCP is required here - if there were three or more strings combined on one circuit, two of them at Isc would exceed the rating of the third and OCP would be required. If OCP is required, then it must be for both + and - conductor.
The two strings may be combined with a simple polaris tap.
Disconnect - both conductors must be opened by the disconnect. A Square D non-fusible disconnect could work here (depending on amperage) and the Polaris fits inside.

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11 years 6 months ago

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Doug Fischer

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