Metal slugs vs fuses in Fronius IG V 5.1 inverter

CqCq
CqCq Registered Users Posts: 8 ✭
in Advanced Solar Electric Technical Forum #1
I am new to this forum, and this is my first post in this section.

Here is a direct quote from the manual of the Fronius IG V 5.1 inverter:

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Polarity Reversal of Solar Module Strings

The inverter comes standard with 6 metal slugs in fuse holders in the connection area. The
inverter is designed so that a reverse polarity of all solar module strings will not cause any
damage to the inverter when these metal slugs are used.


CAUTION! However, there is a risk of damage and fire to the inverter due to reverse polarity of a solar module string when the metal slugs are used.
The reverse polarity of a solar module string can cause an unacceptable thermal
load, which can lead to an inverter fire.

When using metal slugs, always make sure that the polarity is correct before connecting the individual solar module strings.


If string fuses are used instead of the metal slugs, the reverse polarity of an individual solar
module string can cause damage to the inverter and cause an inverter fire.

CAUTION! Risk of damage and fire to inverter due to reverse polarity of solar
module strings when using string fuses.
Reverse polarity of solar module strings can lead to an unacceptable overload to
a string fuse being used. This can cause a strong arc, which can lead to an inverter fire.

When using string fuses, always make sure that the polarity is correct before connecting the individual solar module strings.
=====

So it seems that the inverter is designed to work properly with the shipped metal slugs. When using either metal slugs or fuses there is a fire danger if the polarity of one string is reversed and connected, so that is the same.

So the question is what is the pro and con of replacing the metal slugs with the correctly rated fuses?

My self-installation is almost complete. It is a 4.3kw nominal panel rating, 2 strings of 10 panels each, Isc of each string is 8.1A. I may have to order the fuses if I need to install them, and wait for a while for them to arrive delaying the inspection and approval. So any ideas and suggestions are most welcome. Thank you.
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Metal slugs vs fuses in Fronius IG V 5.1 inverter

    I wonder if they realize they are contradicting themselves:

    "The inverter is designed so that a reverse polarity of all solar module strings will not cause any damage to the inverter when these metal slugs are used."

    However, there is a risk of damage and fire to the inverter due to reverse polarity of a solar module string when the metal slugs are used.

    So in the first sentence they say reverse polarity won't cause any damage, and in the second one they say it can burn the inverter up. That would be damage in my book.

    As for the fuse issue, since you only have two parallel strings you do not technically have to have fuses. An inspector might not see it that way, though.

    I believe the slugs are there in case local requirements demand external disconnect/breakers or other such wiring modifications. As always you need to check the local code demands to see if your wiring complies.
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