Time Delay or Fast Acting Fuses for Supply Side Connections


Wondering what others are using for fuses in the AC disconnects with supply side connections, time delay or fast acting fuses? Since there isn't any surge with grid tied inverters it seems like fast acting would be the way to go but curious to hear other's opinions.
I always use time delay dual element fuses. Sometimes voltage sags and current increases and when the fuses are in a box in direct sunlight during the summer you could get false tripping of your fuses. My engineered plans always call for time delayed dual element fuses.

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Senior Member
On a job of ours the utility (PGE) required Fast Acting. Not sure if that was specific to their transformer located there or that is standard for them.
What was the overall ac wattage and voltage of the system and what size fuses did you use? I know here in kansas and missouri if you use a 7.6kw inverter with 40 amp fuses or an 11.4kw inverter with 60 amp fuses we can get a few false tips in the heat of the summer.

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Senior Member
I always specify RK1 or RK5 fuses to provide a high AIC rating for the disconnect, so I just don't have to worry about the available fault current from the utility. The default type H fuses only give a 10kAIC rating.