A/C disconnect switch bonding


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Old 11-02-17, 10:03 PM
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A/C disconnect switch bonding

I'm getting the material together to install a water proof 240v disconnect switch with fuses for a mini split a/c unit on the exterior of my house. What I would like to do is run two THHN green ground wires along with the current carrying ones in conduit to the switch. One for the exterior disconnect switch and one that will pass through the switch housing to the mini split A/C unit. That way I will not have to break the ground wire at the switch. My concern is that an inspector may not like it for whatever reason, although it makes perfect sense to me.
 
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Old 11-02-17, 11:17 PM
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Welcome to the forums.

One ground wire..... two ground wires...... un-needed but not against code.
 
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Old 11-03-17, 06:19 AM
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Does the unit call for fuses? If not I would use a pullout disconnect .
 
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Old 11-03-17, 11:07 AM
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240 volt A-C disconnects typically have a small ground bar with 2 or 3 holes for both the "Line" side ground and "Load" side ground. Once terminated, the ground wires would never be broken again. I cannot think of a single reason an inspector wouldn't like the way the disconnect is set up.
 
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Old 11-03-17, 01:32 PM
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Since I'm not sure how well the unit will protect the Mitsubishi condensing unit after the usual summertime momentary power failure, I can downsize the fuses in case the unit try's to start against high head pressure. Mitsubishi say's not to go over 25A on the fuses, so I plan on checking the amperage on a normal startup, and sizing the fuses accordingly.
 
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Old 11-03-17, 01:59 PM
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I've read somewhere on this forum that some inspectors require a crimped ground joint in a disconnect switch, that cannot be taken apart. My switch is a Square D top fed through a hub, with a lever handle that has an easy to get to grounding bar. Some handyman could easily unscrew a grounding screw and use the power for multiple sources.

Last year a plumber I know was cutting a galvanized steel water pipe that started arcing. Someone had barely buried a piece of black 14 gauge wire in the ground to feed a backyard lighting fixture with no neutral or ground wire. To complete the circuit they ran another short piece of wire to the nearby galvanized steel water pipe, and the light worked fine until the plumber cut the pipe.
 
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Old 11-03-17, 02:19 PM
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That's called an irreversible ground. A ground that cannot be take apart. That would only be required in a main panel... not at your service disconnect.
 

Last edited by pcboss; 11-03-17 at 04:34 PM.
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Old 11-04-17, 08:19 AM
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Mitsubishi say's not to go over 25A on the fuses, so I plan on checking the amperage on a normal startup, and sizing the fuses accordingly.

You could also use a 25 amp breaker unless the installation instructions specifically say you must use fuses. 25 amp breakers are not terribly common and many people have used fuses to get that exact level of protection in the past, but 25 amp breakers are becoming more common along with the more efficient A-C systems of today. The big box stores even sell them now.
 
 

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