Electrical disconnect for mini split
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wwhitney
In the Trades
The spec sheet should list both MCA (minimum circuit ampacity) and MOCP (maximum overcurrent protection device). The latter may be higher than the former, HVAC is one of the few loads where you can put, e.g. #12 AWG copper wire on a 30A breaker.
Anyway, use the MOCP value for the disconnect rating. Disconnect could be fused or unfused. If your upstream OCPD is properly sized, no real upside to fuses, unless the MOCP says e.g. "30A fuses", then you are required to have actual fuses.
Cheers, Wayne
Anyway, use the MOCP value for the disconnect rating. Disconnect could be fused or unfused. If your upstream OCPD is properly sized, no real upside to fuses, unless the MOCP says e.g. "30A fuses", then you are required to have actual fuses.
Cheers, Wayne
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wwhitney
In the Trades
I suggest a 20 amp circuit breaker, #12 copper conductors, and a 30A fused disconnect (the smallest size). That way if the nameplate really says "max fuse" instead of "max breaker," you can change the fuses to 20A. Note that a 30" wide by 36" area in front of the disconnect has to remain clear, so put the unit to the side of the disconnect, not in front of it.
Cheers, Wayne
Cheers, Wayne
wwhitney
In the Trades
Also worth noting, then, is that if the disconnect is mounted directly on the siding of your residence, it's OK to bring NM cable into the back of the disconnect for the supply side, but you can't use NM cable from the disconnect to the outdoor unit. NM is not allowed outdoors, even in conduit. You can definitely get short lengths of LFNC with connectors, and you may be able to get them with wires preinstalled of the right size. (If you use #10, double check the lugs on the unit are rated for #10s). Otherwise, you'll have to get some lengths of THWN in the correct colors.
Cheers, Wayne
Cheers, Wayne
wwhitney
In the Trades
NM (romex) is OK inside your house, inside an enclosure outdoors, and within your siding.
So if you come into the back of your disconnect mounted on the siding, you can run NM all the way into the disconnect. If you enter the disconnect in any other fashion, you'd need to transition inside from NM to an outdoor wiring method.
Load side, yes, you use a whip with THWN conductors.
Cheers, Wayne
So if you come into the back of your disconnect mounted on the siding, you can run NM all the way into the disconnect. If you enter the disconnect in any other fashion, you'd need to transition inside from NM to an outdoor wiring method.
Load side, yes, you use a whip with THWN conductors.
Cheers, Wayne
My box will be very low to the ground if I come out of my siding because I'm coming out of my crawlspace with wire. Unless I pull some drywall out or fish it through the wall up higher. I figure it will be easier to come out of crawlspace and route it up higher. Is this what I need.
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wwhitney
In the Trades
Option 1: Use UF cable from the panel to the disconnect box. That way you can run it outside for the vertical jog up to your disconnect box. You might want to use a conduit sleeve to protect the vertical leg. Avoids a splice.
Option 2: Set an exterior junction box at the location you come out of the house, enter it from the back with NM. Splice to individual conductors there. Use a short conduit run up to the disconnect.
As to the wires, that's a good choice if it is stranded. Solid is allowed, but I think it would make pulling the wires through the LFNC harder, particularly with the angle connector. Or maybe it would be OK.
Cheers, Wayne
Option 2: Set an exterior junction box at the location you come out of the house, enter it from the back with NM. Splice to individual conductors there. Use a short conduit run up to the disconnect.
As to the wires, that's a good choice if it is stranded. Solid is allowed, but I think it would make pulling the wires through the LFNC harder, particularly with the angle connector. Or maybe it would be OK.
Cheers, Wayne
So I guess I just run a piece of conduit through my crawlspace wall into the junction box, then screw the junction box into the exterior crawlspace wall.
wwhitney
In the Trades
Since the unit is 120V, you don't want a fuse in the neutral conductor. Since most (all?) disconnects are two poles, you'd just one one side with the ungrounded conductor, and splice the neutral conductor straight through. The other side would be unused.
If the second item really is a one pole disconnect, meaning it only has one fuse, and maybe has a set of lugs insulated from the case for splicing the neutral, that would be convenient. But if you look up the manufacturer part number given, there's no discussion of that. So I think that's just a typo on Lowe's website, and the two items are basically the same.
Your other option is to get a copy of the name plate (or wait until you have the unit), and see if it really says "Max 20A Fuses" or instead uses the word OCPD or Breaker. In the latter case you could use an unfused disconnect. I'd be inclined to go that way.
Cheers, Wayne
If the second item really is a one pole disconnect, meaning it only has one fuse, and maybe has a set of lugs insulated from the case for splicing the neutral, that would be convenient. But if you look up the manufacturer part number given, there's no discussion of that. So I think that's just a typo on Lowe's website, and the two items are basically the same.
Your other option is to get a copy of the name plate (or wait until you have the unit), and see if it really says "Max 20A Fuses" or instead uses the word OCPD or Breaker. In the latter case you could use an unfused disconnect. I'd be inclined to go that way.
Cheers, Wayne
I believe I will go the umfused route. Seems like they are more expensive and not as available as there fusible counterparts. I usually shop at lowes. It doesn't look like they have any. I sincerely appreciate your help.
wwhitney
In the Trades
If unfused, sure. 60 amp may be the smallest size they make.
If fused, I'm not sure, there's a question of whether the bigger size will take a 20 amp fuse if need be. I'm guessing 30 amp and under is one physical size, and 31-60 is a different physical size. But in that case they probably make reducers that allow the physically smaller fuse to fit in the larger fuse holder.
Cheers, Wayne
If fused, I'm not sure, there's a question of whether the bigger size will take a 20 amp fuse if need be. I'm guessing 30 amp and under is one physical size, and 31-60 is a different physical size. But in that case they probably make reducers that allow the physically smaller fuse to fit in the larger fuse holder.
Cheers, Wayne
I guess since there is no fuse it doesn't matter if I only need 30 amp. I guess it'd be like using 12 gauge wire on 15 amp circuit.
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