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I'm having a minisplit system installed in a rental. It's a Mitsubishi system. When I did this in other places, sometimes the installer is fine with an unfused local disconnect for the outdoor unit. Other times they insist upon a true fused (not circuit breakers) disconnect for the unit. My current installer is saying an unfused disconnect is just fine. Thoughts?

3 Answers 3

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The instructions for mine (also Mitsu) say nothing about requiring a fuse - just minimum circuit ampacity and maximum overcurrent protection. Installed by approved Mitsu installers, who were just fine with circuit breaker feeding unfused disconnect.

I would suppose that there are installers who mistrust breakers (perhaps based on Stablok?), or possibly LAHJ's with extra-restrictive rules.

I see it as two (or 4) more points of failure and needless extra expense. Some may see it otherwise. That's opinion, though...

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  • Thanks! That's what my current installer is saying too, an unfused disconnect is fine. But another installer at my son's home new build (Fujitsu) was insistent upon a fused disconnect. Again, thanks for the comment! + Commented Apr 26, 2022 at 4:27
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    I find having fused disconnects simplifies troubleshooting, particularly if the wire run from the panel is allowed (240.3) larger overcurrent protection than is allowed by unit. Commented Apr 26, 2022 at 13:34
  • +1 @NoSparksPlease - but that's backwards IMO. It simplifies installation for swapping out a unit to what will almost undoubtedly be more energy efficient (and so the existing OC protection is too much - and with a fused disco, everything can be done outside and not open your panel and then have to find appropriate breakers), not troubleshooting; that's just one more thing that needs to be known-good, +1. If I'm troubleshooting, I want a 'switch', not fuses.
    – Mazura
    Commented Apr 28, 2022 at 4:21
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Code requires 3 things:

  • Circuit breaker or fuse protection appropriate to the unit, but that could be anywhere.
  • A disconnect (fused or unfused) near the unit so maintainers can know it's off - same disconnect rules as you find on any industrial machine.
  • A 120V NEMA 5-15 receptacle nearby to run vacuum pump and recovery pump
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  • Interesting, I never knew about the receptacle requirement. When my HVAC tech charged my system there happened to be a receptacle nearby that I installed for Christmas lights.
    – MonkeyZeus
    Commented Apr 27, 2022 at 12:11
  • @MonkeyZeus that's good enough. Commented Apr 27, 2022 at 22:18
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    2020 NEC Section 210.63. "15- or 20-ampere-rated service receptacle located within 25 feet of the following: Heating, air-conditioning, and refrigeration equipment" ...
    – Mazura
    Commented Apr 28, 2022 at 4:31
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When I was installing my outdoor condenser I asked my journeyman electrician friend about fused, unfused disconnects, and breakers. His reply was as follows:

A fused disconnect is a single point of failure which will trip when the rated maximum of the fuse is exceeded; it's the laws of physics.

I then asked if the dedicated circuit breaker in my panel is not good enough and he replied:

Realistically, you're fine. Think about all of the circuit breakers in use around the world. There's a reason that panel fuses have been phased out in favor of breakers.

In the end I just installed a glorified light switch because the pull-out disconnect would scrape my hands.


It usually just comes down to the installer's preference and personal experience; or whatever is readily available in their van that day.

Code enforcement is like this too. If both options are valid and legal according to NEC then the local ordinance can pick one, the other, or both based on their personal preference.

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