Central AC disconnect

scottysDecember 28, 2009

I am installing central ac for the first time and I am running the line myself. Do I need a fusible or non-fusible ac disconnect switch for my outdoor condenser

unit? The 220v unit will be fed by #10 wire protected by a double 30amp breaker located in the main panel.

Does the fusible switch offer a measure of "extra" protection? or would i be better off with the more compact and cheaper non-fusible disconnect?


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The local disconnect is simply that -- a disconnect. It does not need to be fused and there is no compelling advantage to buying a fused disconnect. A cheapie should be fine here.

[BTW, have you checked the manufacturer's specific recommendation on the breaker size? The reason I ask is that AC units are sometimes fused at the max amps rating to accommodate the starting surge of the compressor whereas the wire is sized according to the minimum circuit. This may be a case where you can use #10 wire on a 40A breaker, so doublecheck that rec' before buying the breaker.]

    Bookmark   December 28, 2009 at 2:55PM
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"It does not need to be fused and there is no compelling advantage to buying a fused disconnect. "

In some jurisdictions it won't pass code enforcement without one!

    Bookmark   December 29, 2009 at 3:56PM
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Just so I'll know for future reference, where, exactly, are a few of these jurisdictions located? Is this a commonplace local code modification in some region or another? Does it apply to residential applications?

Alternatively, if the "code enforcement" is based on the NEC, what's the code cite used to disapprove an unfused disconnect? (Notwithstanding the obvious case where additional overcurrent protection is needed at the point of a disconnect fed from an oversized circuit.)

Has anyone else run into this problem?

    Bookmark   December 29, 2009 at 4:44PM
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I've never run into the requirement for a fusible disconnect in addition to a protected circuit. One of the counties here in Maryland (Anne Arundal County)has some of the most stringent local requirements in addition to NEC, in the country and the only requirement for a disconnect is, a lockable disconnect at the condensing unit.

    Bookmark   December 29, 2009 at 6:09PM
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... There are some units whose manufacturers specify FUSE. This is the case when a fused disconnect will be required.

ie, your A/C unit states "30A Fuse or circuit breaker" = no fused disconnect required. However, if it states "30A FUSE", one IS required.

    Bookmark   December 29, 2009 at 6:18PM
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"However, if it states "30A FUSE", one IS required."

Yep, that makes sense to me, Mike. If a manufacturer specifically calls for a fuse then I reckon you'd have to follow that instruction. What complicates matters, I suppose, is that the term "fused disconnect" is also commonly used to include disconnects with breakers. Similarly, a topical heading like "Fusing" often refers to overcurrent protection in general, whether by breaker or fuse.

(BTW, I wasn't aware of manufacturers who specifically require fuses for small residential A/C units these days. But if they're out there, I agree with you.)

    Bookmark   December 29, 2009 at 7:58PM
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