Mini split wiring question

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Old 06-29-17, 02:18 PM
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Mini split wiring question

I bought this system from Home Depot with the following specs:

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my setup will be:

10/2 liquid tight whip from condenser to 30A fused disconnect.
12/2 BX cable from main panel to disconnect (roughly 80 feet through attic)
20A breaker at main panel

my question is, can I use a bigger breaker at the main panel and if so whats the max?

the reason i ask is my panel is an old Zinsco panel and breakers are insanely expensive. I have a spare 40A single pole breaker laying around but I'm thinking that's way too big for this setup?

Also, roughly about 6-7 feet of the BX cable will be running down the outside wall to the disconnect. Would I need to run it through conduit or liquid tight even though i'm going to use a line set cover?
 
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Old 06-29-17, 02:32 PM
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Welcome to the forums.

For that run I would have used #10 but apparently the #12 was already in place. The code allows larger breakers to be used with A/C's to account for startup load.
30A max in your case.

I make it a policy to never over protect the size wire I've run regardless of the code.
I would try running that on the 20A breaker first before considering an upsize.

What can be said about the BX..... it's not supposed to be outdoors under any condition.
 
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Old 06-29-17, 02:45 PM
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BX cable is an obsolete term for some types of armoured cable. If you mean MC cable it can only be used outside if rated for outside use. Why not just use PVC conduit with individual conductors or just run UF cable all the way sleeving it with conduit outside.
40A single pole breaker laying around but I'm thinking that's way too big for this setup?
It is and if you used it to a fused disconnect you would have to use #8 wire.

Of course you know the Zinsco box is not safe for use don't you? Replacing it would be ideal. If you have the 2-pole 40 amp breaker. I might suggest a modern subpanel next to the main panel powered by the 40 amp breaker. Then run your new circuits from there.

Why are you using a fused disconnect? Most residential A/Cs only need a non fused disconnect. Does the manufacturer's instructions require it?
 
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Old 06-29-17, 03:45 PM
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Thanks for the welcome.

so using UF #10 cable W/30A breaker at main and non-fused disconnect would be a better option?

the manufacture instructions don't specify fused or non-fused although I've read on other threads that if the tag lists "MAX FUSE" only, then a fused disconnect would have to be used. Is there a disadvantage in using a fused disconnect? I figured it would be an extra layer of protection, especially with the outdated Zinsco panel.

the panel will be replaced in due time but it's what i got to work with for now.

thanks for the help!
 
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Old 06-29-17, 05:07 PM
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so using UF #10 cable W/30A breaker at main and non-fused disconnect would be a better option?
Yes, unless the manufacturer of your A/C requires a fused disconnect. Normally on residential A/Cs fused disconnect isn't required because the protection is built into the A/C. UF will need to be sleeved for protection where it runs down the wall.
Is there a disadvantage in using a fused disconnect?
They're more expensive.
 
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Old 06-29-17, 05:18 PM
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You would use a fused disconnect if you had a larger supply cable to a smaller unit.
I.E. 30-40A feed to 20A unit. You would use 20A fuses.

You can use a fused disconnect in place of a non fused one. The breaker, if smaller, sets the protection level. If you have a 20A breaker with 30A fuses...... the fuses will never blow but the breaker will trip on fault. That is ok.

A/C's list fusible size but breaker is also ok.

I just did a service call where customer had a 40A breaker feeding a fused disconnect with 60A fuses. The A/C tech told the customer the fuses where blown, to call an electrician, charged him and left. The 60A fuses will NEVER blow if protected by a 40A breaker.

The fused disconnects run approx $15 (plus the fuses) while the non fused run around $8.
BUT..... the fused disconnects are of a better quality overall.
 
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Old 06-30-17, 07:40 AM
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Your data label calls for fuse protection. It does not say max breaker size.
 
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Old 06-30-17, 10:00 AM
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I don't believe that the word "fuse" being on the information label literally means that a fuse must be used as the circuit OCPD. A 30A breaker on #12 for that A/C circuit without a fused disconnect is fine. With that being said, I agree with Pjmax and would just use a 20A breaker with the #12.
 
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Old 06-30-17, 11:00 AM
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I don't believe that the word "fuse" being on the information label literally means that a fuse must be used as the circuit OCPD. A 30A breaker on #12 for that A/C circuit without a fused disconnect is fine. With that being said, I agree with Pjmax and would just use a 20A breaker with the #12.
I've looked everywhere for a 30A non-fused disconnect but can't seems to locate one. HD has a 60A 120V/240V non-fused. would that work with the setup you mentioned?
 
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Old 06-30-17, 11:02 AM
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Yes, you need a disconnect that is rated at least 30A. The 60A will be fine.
 
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Old 06-30-17, 11:28 AM
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The labels on the equipment coming in from Asia are not always correct or accurate.
 
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Old 06-30-17, 12:00 PM
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How is anyone to discertain if the labels are correct?
 
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