How to fuse the DC side of a Multi RS?

Q&A and troubleshooting
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Hi!

What’s the appropriate way to fuse the DC side of a Multi RS? There are two places where fusing might apply:

  • From PV: the multi RS includes two fuses, one for each MPPT, right after the MC4 inputs (see picture) but there’s no info about them in the manual, nor they show up on the official pics (must be from and older revision). Has anybody pulled one of those out to check their nominal current? What type of fuses are they? And are they easily replaceable? I assume it would it be redundant to add additional fuses coming down from the panels.

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  • From battery: I read a post on this forum ( New Multiplus RS Solar + Pylontech --> all in one 19" rack ) where someone connected the Multi RS to the batteries without fusing, and the consensus seemed that it was ok to do so. Is that the case? The batteries would be 2x Pylontech US5000 with internal protection against short-circuit and overcurrent. Would the MEGA fuses be useless in this case?

Thanks!

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Over short distances, with adequate wire sizing, connecting a MULTI Rs to pyolontech is ok, with no fusing, as the pylontech batteries are well protected against over current.

With longer cable runs from the Multi RS to the battery, then the cables may be subject to damage, and need to be protected by fuses.

On the PV side, if the Multi’s PV input is fused, then only an external 2 pole disconnector is required, UNLESS local regulations require additional fusing - eg, if 3 strings are externally combined on one input.

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Thanks Mike!