Proper Circuit for 220 A/C

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I have an existing circuit from an old central air unit, dble pole 30Amp breaker, 12/2 w/g wire. Can I safely use this circuit for a 220 window A/C, 18500 BTU, rated at 9 Amps?

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Type: Question • Score: 8 • Views: 3,098 • Replies: 22

[+3] - timur - 06/25/2013[quote=Dale]I can envision all kinds of shorts or other destructive conduction between 9 and 30 amps burning down mul's house [/quote] Yeah? Tell me which ones... But before you come up with...

@mulder75,

What does your electrician say? You, of course, consulted with a qualified electrician right? How did it function with the previous A/c unit?

1 Reply

@Ragman,

The circuit worked fine with the previous unit. The compressor went bad, and I could never afford to replace it. No, I have not consulted with an electrican. I wired up my cooking stove, and most of my basement. If you feel I should hire an electrican, the entire posting is moot, true?

1 Reply

@mulder75,

It costs you nothing to ask an electrician about this...I'm just saying.

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@mulder75,

The use of a 30-amp breaker for a load of only 9 amps is pretty risky

1 Reply

@dalehileman,

why would you say that?

Admittedly though, I'm seeing 40 A circuit-breaker on mine.

1 Reply

@Ragman,

Quote:

why would you say that?

I can envision all kinds of shorts or other destructive conduction between 9 and 30 amps burning down mul's house

2 Replies

@dalehileman,

dalehileman wrote:

Ragman wrote:
dalehileman wrote:
The use of a 30-amp breaker for a load of only 9 amps is pretty risky

why would you say that?

I can envision all kinds of shorts or other destructive conduction between 9 and 30 amps burning down mul's house

A 30 amp breaker should only be used with wiring that can handle 30 amps (presumably a certain gauge of wire, and a certain amount of insulation around the wire). But I don't see any unusual risk to drawing only 9 amps through a 30 amp breaker, so long as the circuit can safely handle 30 amps.

But I have zero qualifications as an electrician.

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@mulder75,

I think you need to discuss this matter with an electrician because it includes risk in it so an expert is the only one who can help you out in this matter.

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Dale wrote:

I can envision all kinds of shorts or other destructive conduction between 9 and 30 amps burning down mul's house

Yeah?
Tell me which ones...

But before you come up with some dumb answer, and in the light of the OP's data, check out this:

American wire gauge

1 Reply

@dalehileman,

dalehileman wrote:

Quote:
why would you say that?

I can envision all kinds of shorts or other destructive conduction between 9 and 30 amps burning down mul's house

I too am curious what kind of destructive conduction you are referring to.

By the way, a short won't cause the problems you seem to envision. If the short is such that it pulls less than 30 amps the 12/2 wire will handle it. If it pulls more than 30 amps it will blow the breaker before it overheats the wires.

1 Reply

@timur,

Quote:

Yeah? Tell me which ones...

A family of mice builds an elaborate nesting system between a grounded outlet and an exposed hot wire junction from which the wirenut had become dislodged, in which their toilet is built across an absorbent span of decomposing wood in a nest of aluminum foil capable of retaining a significant volume of liquid. Eventually conduction of only a few hundred milliamperes melts a discarded candle supporting a batch of steel wool, which falls into the gap so as to initiate a series of pulsations less than 30 amps when the sparks start a fire

3 Replies

@dalehileman,

Wow?! Assuming that could be a possibility, what are the odds of that EVER happening? Is it one in a million or 100 million?

Back to reality and rationality, the common sense answer is to ask a licensed electrician.

1 Reply

@parados,

Quote:

I too am curious what kind of destructive conduction you are referring to.

ara see my posting #….861 above

Quote:

By the way, a short won't cause the problems you seem to envision.

Call it whatever you like: Electric current flowing through a substance of low enough resistance to cause heating but high enough to maintain flow less than 30 amps

Quote:

If the short is such that it pulls less than 30 amps the 12/2 wire will handle it.

Granted. However I can easily imagine dozens of situations in which a lesser flow owing to foreign objects or malfunction of the load or could easily ignite adjacent or surrounding combustibles as I described

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@Ragman,

Quote:

Is it one in a million or 100 million?

Three million seven hundred and sixty million, nine hundred forty

I am in fact one such victim. I had thought my rock-tumbler motor was getting pretty hot but I never imagined it would set my porch afire one night. Fortunately we were home, in bed, still awake, the bedroom window was open so we heard the crackling sound

Destructive conduction, pretty common occurrence: Doubtless short circuit over part of the field winding, increasing current over the rated value but not high enough to trip the breaker. I can easily imagine this sort of thing happens throughout the world scores if not hundreds of times a day, often starting a fire

Just how many caused by a breaker of excessively high rating for the load I couldn't guess

1 Reply

@dalehileman,

And that relates to the OP's question in which way?

When I said you would come up with a dumb answer..

1 Reply

@timur,

Quote:

And that relates to the OP's question in which way?

Can I safely use this circuit for a 220 window A/C, 18500 BTU, rated at 9 Amps?

Not as safely as a breaker of lower rating

Tim, a short is literally a new path for the flow of current caused for instance by two conductors having been pushed together. It is very common occurrence in a load consisting of multiple turns, for only part of a winding to be shorted, enough to cause heating but not to trip the breaker. For instance in a motor, either field or armature, two or more adjacent layers of the winding might short, reducing overall resistance and thereby causing an increase in current

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@dalehileman,

Wow. What a bullshit argument that has nothing to do with the size of the breaker, the wire, or the draw of the AC unit on the circuit. A 2 amp breaker could cause the fire under your scenario so it has nothing to do with the 9 -30 amp you claim is the problem.

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@dalehileman,

Quote:

I am in fact one such victim. I had thought my rock-tumbler motor was getting pretty hot but I never imagined it would set my porch afire one night. Fortunately we were home, in bed, still awake, the bedroom window was open so we heard the crackling sound

A faulty device really has little to do with the safety of the circuit. The circuit is still safe for the load. I suppose you would argue that if someone put an electric heater up against drapes, the breaker should be able to detect that and prevent a fire.

2 Replies

@parados,

Par our dilemma is purely semantic. He asks, "Can I safely use this circuit…." and I replied, "Not as safely as a breaker of lower rating"

0 Replies

Proper Circuit for 220 A/C

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