Circuit amperage question

In a word, Yes

Most likely, Jenny. Also, remove the cover from a light switch and look at the size wire going to the switch. Then look at the wire to the socket you are planning to use. if the wire at the socket is larger you can pretty safely assume that it is. The "20" molded into the handle of the breaker means that it is a 20 amp circuit but the visual check will provide more proof. If all else fails, see if you can find an electrician who will look at it for you without charging you to do so.

Jim Chandler

If the house was built to code, a breaker marked "20" should feed a circuit suitable for a 20 amp load. But when you buy a used house you can often get some nasty surprises. :(

I'd probably go ahead and assume that you have a 20 amp circuit but I would check to see if there is anything else on the same circuit. Snap the breaker 'off', see what lights and outlets go dark. A stray floor lamp or cloaset light is no big deal but your new A/C will not coexist happily with any kind of heating appliance like a toaster oven or hair dryer.

If the house has full conduit, it is usually not that big a deal to run a new pair of wires to give one outlet a dedicated circuit. BTDT for an permanent install of a wall A/C unit.

Stay cool!

snipped-for-privacy@msn.net wrote:

It's a 20 amp circuit, you can safely plug a 15A appliance in.

Grant

What would lead you to suspect that it is not a 20A circuit?

That would be a minimum rating -- perfectly OK to connect it to a 20A circuit. Probably *better*, in fact, if there's anything else on the circuit in addition to the AC.

Probably safe to make that assumption, yes. You certainly have a 20A circuit breaker. The only question is whether the wire on the circuit is appropriate for 20A, or if some knucklehead in the past replaced a 15A breaker with a 20A, without changing out the wire too. If you're in doubt, consult an electrician.

Of course, she could whip out her trusty li'l digital calipers, and measure the goddamm wire. #14: .065 #12: .080 #10: .100

Course, then, to really make sure, you'd proly have to open each junction box, to make sure someone didn't pull a fast one. Then, actually test the breaker, in case comeone pulled a fast one.

Then, check calibrate the calipers, to make sure someone dint pull a fast one.

She's sure shit is to code. Why the Q??

Oh, those dimensions would be the bare copper, not the insulation. Oh, and make sure when you measure the bare copper, you don't get caliper edge in the nick sometimes created by stripping the wire.... Cain't be toooo careful, y'know.....

All Jenny needs to do is to "calibrate" her Mark 1 Eyeballs (Hairy) with a few samples of #12 and #14 Copper wire with the same insulation as the house (TW or THHN), and you can easily spot when somebody has cheated. You double check the eyeball measurements by reading the markings on the wire, that's why they get printed on.

If the circuit starts at the panel properly on #12 wire, and finishes at the receptacle properly on #12 wire, and there are no other obvious mis-breakered circuits in the panel or the house, the chances are really good that it's #12 wire all the way and perfectly safe to use breaker protected at 20 Amps.

Where the fun usually starts is when Joe Handyman does his own electric work doing a room addition, runs out of #12 wire halfway through the day, and rather than run to the store to get more just switches over to #14 wire in mid run - but forgets (or doesn't know) to swap out the breaker to a 15A.

Or Joe Handyman puts in a new panel and starts changing out breakers and doesn't worry about changing an old 15A with a new 15A, and just tosses in all 20A breakers.

If the old breaker was a 15A there's usually a reason they derated the circuit, even if it starts out on #12 wire. You have to check out why it was done that way before arbitrarily increasing the breaker.

Might be that circuit is connected to a refrigeration compressor or other equipment that calls for a 15A breaker maximum, might be a wire gauge switch in mid-run.

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Jenny: Please read the paragraphs below and acknowledge it. And anyone else that does any of their own electrical should read, too.

WARNING: If you find Aluminum wire has been used in your house or mobile home for a convenience receptacle or lighting branch circuit that goes to multiple junction boxes and multiple devices, STOP and call in a professional to do ANY work.

Aluminum branch circuit wiring may be found in site-built homes and manufactured housing ('mobile' or 'modular' homes) built from the late

1960's through early 1980's, depending on state and local building codes - some areas allowed it early, some never did at all.

It takes proper retrofitting with special compression connector "pigtails" at each junction box along each circuit run to make it safe. If the house has not been "pigtailed" as a retrofit, and someone doesn't follow the special precautions when doing any small repair work after that (special anti-oxidant compound filled wirenuts and special techniques) the conditions can be ripe for a house fire.

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Aluminum wire is still legal to install, but only if it makes only one stop at each end, either between two power panels (main to sub) or running from the panel to a heavy appliance like the range, oven, clothes dryer or air conditioner.

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Interesting... didn't know that. Got a citation for that in the NEC? All I can find is Article 110.5: "Conductors normally used to carry current shall be of copper unless otherwise provided in this Code."

I'll have to go find the exact language they refer to with that cryptic "unless otherwise provided in this Code", but it's in there.

They still sell AL, I still use it (don't like to, but people balk at doubling the bill to use Copper), and the Inspectors still pass it.

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I'm sure it is -- I wasn't doubting you, and I apologize if I gave that impression. I just haven't ever seen it, and I'd like to know the details.

As an "old,old (age) person that started his working career in the mid 60's I can tell you exactly why aluminum was (is) frowned upon. It is primarily due to aluminums large rate of expansion/contraction. Here is about 3 of the most common problems,

Most electricians use wire skiners that would occaissionaly put a tiny nick in the wire, when you put aluminum on a steel screw the expansion rates of aluminum vs steel allow the nick to fracture. The load also generates heat that amplifies expansion/contraction problems.

Aluminum if crushed by over tightining stays crushed, and once the circuit cools it is no loger as tight as it was. Do this a couple thousand times (2-3 years ) you can have a loose connection.

Aluminum oxidizes as do other dissimilar metels when joined. In many humid locations a protective gel (Penetrox) must be use religiously.

The common sizing for curcuits was to go up 1 wire size from copper.

These expansion problems are exacerbated by two undesirable properties of aluminum when compared to copper: greater coefficient of thermal expansion, and higher electrical resistance. So not only does it expand more than copper when heated, it also is heated more.

It's not necessary for the circuit to be energized, ever, for the connection to loosen. Aluminum exhibits a considerable degree of cold flow (when compared to copper), and will "ooze" away from an overtightened connection even if it's never heated.

And right there is the biggest problem. Copper oxide is a good electrical conductor. Not quite as good as metallic copper, but still a good conductor. Aluminum oxide is an electrical *insulator*.

Antioxidant compounds should be used even in non-humid environments.

Two AWG gage sizes, actually, in almost all cases. At smaller gages (6AWG and under), that's equivalent to "next size up" for electrical conductors, since they don't come in odd numbers. But you can't replace 4AWG copper with 3AWG aluminum; you need to use 2AWG. Similarly, 3 Cu = 1 Al, 1/0 Cu = 3/0 Al, etc.

] Even with copper, I sort of shudder at the notion of wire nuts. In my

1920-ish house, connections are wire nutted AND soldered!

"Proctologically Violated©®"

Good ol knob and tube wiring .. it not only provided power but when equiped with a 30A fuse it gave you warmth too

Hi guys,

Thanks for that. I asked the question as I was unsure if the 20 meant tripping current or running current. If it was tripping then that would suggest the circuit is 15A to my simple mind. Being a 20A circuit is even better. Thanks again, the A/C is on it's way.

As a journeyman inside wireman (and I've the ticket to prove it), I had to smile at most these posts...especially the involving the use of calipers to determine wiresize...HAHAHAHAHAHA !! (if you can't tell by sight, probably best to stay out of the circuitry)

A breaker (or fuse) protects circuitry (the house wireing), equipment and people. Ideally you want the circuit beaker rating to closely match the rating of the equipment being protected. The air conditioner is rated at 11 amps. A 15 amp breaker is closest and most ideal for it. But a 20 amper will be just fine (and makes allowances for other minor things on the same cicuit like lights). A navy electrician would no doubt use 12 gauge wire with a 20 amp breaker and it will almost certainly be ok.

Geez, I wouldn't make things so complicated....chill out.

That's the maximum safe continuous current - but those ratings are set VERY conservatively, the wire is good for quite a bit more. But in the interest of safety the Codebook says "for household convenience circuits you shall rate 10-Gauge for 30 Amps, 12-Gauge for 20 Amps, and 14-Gauge for 15 Amps, Period".

Even with more modern THHN (Nylon over PVC) or XLPE wire insulation that's safe for 90-C operation, they retain the old ratings from the Rubber insulated wire.

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