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Old 05-07-2019, 07:22 PM   #1
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Default Whats the best way to size a disconnect for a AC Condenser

I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.
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Old 05-07-2019, 08:14 PM   #2
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Originally Posted by Sparky1744 View Post
I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.
its a disconnect. any disconnect at a rating of more than 208/30 will do. if it is fused, you will need to comply with 440. I'm answering the question you asked, but not sure if you didn't ask the question you thought you asked ?

You didn't post horses or locked rotor, but here's the beginning of the article you should read in 440:

Quote:
440.12 Rating and Interrupting Capacity.
(A) Hermetic Refrigerant Motor-Compressor. A disconnecting means serving a hermetic refrigerant motorcompressor shan be selected on the basis of the nameplate rated-load current or branch-circuit selection current, whichever is greater, and locked-rotor current, respectively, of the motor-compressor as follows.
(1) Ampere Rating. The ampere rating shall be at least 115 percent of the nameplate rated-load current or branchcircuit selection current, whichever is greater.
Exception: A listed unjilsed motor circuit switch, without jitseholders, having a horsepower rating not less than the equivalent horsepower determined in accordance with 440.12(A)(2) shall be permitted to have an ampere rating less than 115 percent of the spec~fied current.
(2) Equivalent Horsepower. To detennine the equivalent horsepower in complying with the requirements of 430.109, the horsepower rating shall be selected from Table 430.248, Table 430.249, or Table 430.250 corresponding to the ratedload current or branch-circuit selection current, whichever is greater, and also the horsepower rating from Table 430.251(A) or Table 430.251 (8) corresponding to the locked-rotor current. In case the nameplate rated-load current or branch-circuit selection current and locked-rotor current do not correspond to the currents shown in Table 430.248, Table 430.249, Table 430.250, Table 430.25J(A), or Table 430.25J(B), the horsepower rating corresponding to the next higher value shall be selected. In case different horsepower ratings are obtained when applying these tables, a horsepower rating at least equal to the larger of the values obtained shall be selected.
(B) Combination Loads. Where the combined load of two or more hermetic refrigerant motor-compressors or one or more hermetic refrigerant motor-compressor with other motors or loads may be simultaneous on a single disconnecting means, the rating for the disconnecting means shall be determined in accordance with 440.12(B)(l) and (B)(2).
(1) Horsepower Rating. The horsepower rating of the disconnecting means shall be determined from the sum of all currents, including resistance loads, at the rated-load condition and also at the locked-rotor condition. The combined rated-load current and the combined locked-rotor current so obtained shall be considered as a single motor for the purpose of this requirement as required by (l)(a) and (l)(b).
(I'm stuck on NEC2014, but I don't think much has changed here)
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Old 05-07-2019, 10:31 PM   #3
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Cheapest one that meets the hp. Usually a 60 amp non fused for less than 20 bucks.
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Old 05-08-2019, 02:29 AM   #4
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Originally Posted by Sparky1744 View Post
I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.
It's a puppy, but still you'll be using a 30A frame size safety switch.

Is this an apartment or micro commercial? I say that because 208 VAC single phase is not seen in ordinary commercial.

Most condensers that small are dual voltage rated anyway. They expect 240 VAC but will put up with 208 VAC.

Even cheop residential discos -- with fuse pull blocks -- are still fused -- and the label is telling you to got with 25A fuses -- time delay or slo blow.

The Hertz is irrelevant to you.

You might go with #12 conductors. as 12.1 FLA is 0.1 Amps over the 80% of 15Amp #14 limit. But this is fundamentally a motor load. So even #14 wire will suffice.

Read 440.

In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)
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Old 05-08-2019, 07:06 AM   #5
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Originally Posted by telsa View Post
It's a puppy, but still you'll be using a 30A frame size safety switch.

Is this an apartment or micro commercial? I say that because 208 VAC single phase is not seen in ordinary commercial.

Most condensers that small are dual voltage rated anyway. They expect 240 VAC but will put up with 208 VAC.

Even cheop residential discos -- with fuse pull blocks -- are still fused -- and the label is telling you to got with 25A fuses -- time delay or slo blow.

The Hertz is irrelevant to you.

You might go with #12 conductors. as 12.1 FLA is 0.1 Amps over the 80% of 15Amp #14 limit. But this is fundamentally a motor load. So even #14 wire will suffice.

Read 440.

In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)
I don't bother with a fused disconnect if the max ocpd rating is a standard sized breaker. I pop in the right sized breaker, then use an $8 60A pull out style non-fused disco.

ETA: This is obviously for single phase small A/C systems. Thought I'd throw in that caveat.
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Old 05-08-2019, 11:59 AM   #6
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25 amp breaker (if you can get one), 14 awg or larger feed - i'd run at least 12. And a cheap $7 60 amp pull out non-fused disconnect from home creepo. If you can't find the 25 then, use a 30 and a $12 fused disconnect from the creepo with 25a time delay fuses.
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Old 05-08-2019, 01:45 PM   #7
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Whats the best way to size a disconnect for a AC Condenser?
You size it by profit 1st and amperage 2nd
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Old 09-09-2019, 06:14 PM   #8
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Originally Posted by Sparky1744 View Post
I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.
Most AC has the MFG information on them. Is this coming from a 208 3 phase. We do not have 208 single phase in this part of the world
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Old 09-09-2019, 07:40 PM   #9
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We do not have 208 single phase in this part of the world

Sure we do. Any two legs of three phase 208 is single phase 208.
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Old 09-09-2019, 08:03 PM   #10
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Sure we do. Any two legs of three phase 208 is single phase 208.
My question was it coming from a 208 3 phase.
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Old 09-09-2019, 08:06 PM   #11
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My question was it coming from a 208 3 phase.

It would have to be in order to be 208. Lots of apartments and offices are fed with a 208/120 three phase service and distributed to the units as single phase.
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Old 09-09-2019, 09:13 PM   #12
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In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)
Looseleaf?
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Old 09-09-2019, 09:32 PM   #13
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In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)

Can you post a copy of this local amendment? Surely, you own a phone capable of taking pictures of this document. Or maybe a link to the PDF this amendment is contained in.
I personally would locate the AHJ in question and grovel for the return of your balls which he is currently carrying in a brown bag and taunting you with
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Old 09-10-2019, 12:48 AM   #14
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Most AC has the MFG information on them. Is this coming from a 208 3 phase. We do not have 208 single phase in this part of the world
If you're going to use the phrase "this part of the world", you really should fill out your profile, so we know where "this part of the world" is. We have members from all over the world, (even Canada), and little details, like location, are helpful in providing meaningful replies.

In this part of the world, we can only get single phase 208v, from 3-phase 208v, otherwise it's 120v. Also, all A/C equipment must have a nameplate, or it won't pass inspection.
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Old 09-10-2019, 12:54 AM   #15
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Originally Posted by telsa View Post
It's a puppy, but still you'll be using a 30A frame size safety switch.

Is this an apartment or micro commercial? I say that because 208 VAC single phase is not seen in ordinary commercial.

Most condensers that small are dual voltage rated anyway. They expect 240 VAC but will put up with 208 VAC.

Even cheop residential discos -- with fuse pull blocks -- are still fused -- and the label is telling you to got with 25A fuses -- time delay or slo blow.

The Hertz is irrelevant to you.

You might go with #12 conductors. as 12.1 FLA is 0.1 Amps over the 80% of 15Amp #14 limit. But this is fundamentally a motor load. So even #14 wire will suffice.

Read 440.

In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)

Isn't that pretty much standard anywhere? I've never seen #14 on a commercial project, except maybe BMS.
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Old 09-10-2019, 01:37 AM   #16
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Isn't that pretty much standard anywhere? I've never seen #14 on a commercial project, except maybe BMS.
Lay off Telsa. After all his old girlfriend was a penthouse pet of the year. I think she couldn't take all his constant studding her. He's a beast.
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Old 09-10-2019, 06:17 AM   #17
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Originally Posted by Sparky1744 View Post
I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.
I would use one of those $6 30amp non fused pull-outs unless someone wants to pay for something fancy.
Im not a big fan of installing a fused disconnect at a consumer site. If its a commercial job, and they wanted to pay for it, I would install a small fused disconnect to make it easy for the maintenance guy.
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Old 09-10-2019, 06:22 AM   #18
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Originally Posted by Sparky1744 View Post
I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.
I would use caution sizing the conductors. They call out 14.8 to force you into #12s but, you need to pull out the installation manual. That little book will call out the conductor size based on the length of the run. You should follow those recommendations.
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Old 09-10-2019, 02:32 PM   #19
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Looseleaf?
Actually, yes.
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Old 09-10-2019, 03:13 PM   #20
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Isn't that pretty much standard anywhere? I've never seen #14 on a commercial project, except maybe BMS.
It's an unwritten schoolyard "standard". In some cases job spec. Very similar to using 3/4" pipe for everything. I never saw 1/2" pipe once in commercial work. Even for a pair of conductors going down to a single switch, we used 3/4 pipe.

But it's not code.
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