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Old 03-13-2019, 09:17 AM   #1
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Amp rating on AC unit

All,

A question for you electrical genius.....

On my 16K BTU Airrrr AC unit the specs show the fuse rating as 20 max 14 min. Why the difference?

If it can run on 14a, why put a larger fuse in?

As I understand AC units, they usually put out a high power or serge when starting then operate at a lower power.

I'm looking at power requirements for a shore power plug in, on another thread. Thanks
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Old 03-13-2019, 09:29 AM   #2
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I would imagine that has to do with breaker style (slow blow or instantaneous). There is a peak surge every time the compressor starts and the ranging of fusing is likely to compensate for that. As is often mentioned on TF, you are fusing to protect the circuit (wire size and plug rating). I would focus on that more than the unit. If you're wire size will handle 20 amps, go that route with your 30 amp shore power plug.

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Old 03-13-2019, 09:32 AM   #3
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Fuses and breakers (most) have a current vs time trip curve, which effectively allows a brief current surge above the trip point. So a 20A breaker can handle 30A for say a few seconds, but will trip at 25A in say 20sec. Hit it with 50A and it will probably trip instantly. This varies between designs and mfr's.

There are breakers that are fast acting, basically anything over setpoint causes a trip.

If your pump will be fed by the same circuit, I'd go with a 20A breaker. My 12.5kBtu unit with pump can draw about 12A, and I run it through a 15A breaker. A 16 with pump might trip a 15A breaker.
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Old 03-13-2019, 09:42 AM   #4
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To Ski's point above, the amperage specs for A/C units generally exclude the raw water circulation pump which typically adds a couple of amps to the total.


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Old 03-14-2019, 06:51 AM   #5
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All large induction motors have a measured LRS (locked rotor start) number that usually is 2x to 3x the amperage to operate the unit.

Air cond can install special devices to lower the LRS if dock or noisemaker power is minimal.
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Old 03-14-2019, 07:24 AM   #6
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My interpretation of that spec would be that you need a minimum of a 14A breaker to run the unit, and anything less will trip in normal operation. And the units wiring is can only handle 20A of fault current, so your breaker can't be any larger than that without creating a fire hazard in the unit itself. So using common breaker sizes, you could use a 15A or 20A breaker.


Good point made by others about possible piggy back loads like the circulation pump. You would have to dig deeper to see if that's included in the 14A min, or in addition to the 14A min. Or just assume it's in addition to, and use a 20A breaker.
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Old 03-14-2019, 10:00 AM   #7
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Good points and thx

I wonder if the install manual goes into more detail with the proper breaker with mention of slow or fast blow factors. Need to pull the panel to see what size I have. (wish they'd put that number on the switch).

As for other items like the water pump (only 1.2a), I'll figure them in separately as to the needs of a shore power supply.
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Old 03-14-2019, 10:11 AM   #8
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Quote:
Originally Posted by Seevee View Post
All,

A question for you electrical genius.....

On my 16K BTU Airrrr AC unit the specs show the fuse rating as 20 max 14 min. Why the difference?

If it can run on 14a, why put a larger fuse in?

As I understand AC units, they usually put out a high power or serge when starting then operate at a lower power.

I'm looking at power requirements for a shore power plug in, on another thread. Thanks
What's the hertz rating of your ac? Is it a range 50~60hz or a fixed 60hz?
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