Hardware specs - amperage thoughts

I see a lot of talk about devices not rated for high amp. I get that. I also feel it's somewhat of a gimmick - or just call it a place of confusion for john q public.

In the US, most house circuits are 15A. I personally have never seen a power cable go through a wall just to one socket. it's always a daisy chain through a few rooms.
My Seedan/CMARS outlets are rated at 10A. that is a ton of juice. The idea that someone truly needs a device that can handle 20A or more... always makes me shake my head.
Perspective - a blow dryer is 1500w. (ymmv). 12.5 A. Now. I was a hardware engineer when I got out of college, specializing in AC/DC. When we built something we used the 'factor of safety' rule. thats 10% over design. Your 1500w hair dryer really puts out 1350w at max. 11.3A
The 10A rated outlet is 10% off as well. it's really 11A. I realize we're close here but this is just point of discussion - spending tons of money to get a 20A rated outlet or relay is nuts since the circuit is a 15A outlet to begin with! What we need to be looking for is 15A rated outlets!

I'm not following all your comments.

In any case, when a circuit breaker is rated for 15A, it probably uses 14 gauge wire that can only safely handle 15A (and for a limited distance). And, all the outlets and switches are rated for 15A.

The reason for the "safety factor" is to allow for age and other unpredictable things--not so someone can just blindly go ahead and try pulling 17+ Amps. That's a fire waiting to happen.

And, there are some devices that are best plugged into a 20A outlet (some even come with associated "sideways" plug).

The real concern I have is with how "derated" every thing is when you're dealing with LED bulbs.

A dimmer (or even a switch) rated for, say, 1500 watts of incandescent load--is often only good for about 300 watts of LED load. :frowning:

I'm in no way qualified, but still happy to offer an uneducated guess... :slight_smile:

Could the higher load plugs be more for beefier tools, welders and alike?

In a more common situation, could the higher load wiring be required for combinations of devices that, together can draw more power, so in a bathroom heat lamps on the same wiring as a couple of lights and a fan. I know, at least in terms of the 4-gang switch I put in my bathroom, the electricians told me to buy another one rated high enough to cover the 4 heat lamps that were connected to it along with a bulb and an exhaust fan.

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In my house, 20Amps go to the water heater, the baseboard heaters, cloth dryer and a saw in my shop that would always pop the 15 amp breaker. This last one required the addition of a new breaker, a new power cable and a new outlet. All other plugs and lights are on 15 amp breakers.


In my house the 20A breakers (and 12 gauge wiring) go to:

dishwasher, kitchen microwave, garbage disposal, clothes washer, all other kitchen outlets, all garage outlets.

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Just imagine how many amps your "5 HP" shop vac would pull if it was really 5 HP!


Very interesting that some have 20A for kitchen appliances and others don’t!


It would be interesting to know what new infrastructure may be needed to prepare for electric vehicles of the future.... I can only imagine 15A may not cut it....


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Yes. Currently, home level 2 chargers in North America typically use either 16 or 32 amps at 240V. Part of my remodel will be to run a new circuit for a Level 2 charger.

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Interesting they are 240V, I thought you guys ran on 210V or something lower than us...

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Residentially, we typically have three wire service into a house. One neutral, and two 110-120V hot legs that are 180 degrees apart, so the potential difference between the two hots is 220-240V.

Most circuits are 110-120V (so one hot leg and a neutral). Larger appliances, like an electric stove, electric dryer, or A/C compressor, are 240V (both hot legs and the neutral).

Commercial tends to be three-phase, so three hots at 120V and one neutral. The three hots are 120 degrees separated from each other.

That probably explains the different plugs then, we typically have 3-proonged outlets.

And yes, three-phase is less common, but not completely out of the ordinary, I think my parents had that put on during their renovation when I was growing up.

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So do we. One hot, one neutral, one ground. But the hot is at 120V.

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I have a 50A circuit for my EVSE (*), using 6 gauge wire (it's a very long run). That lets me charge our cars at 40A/240V. There's a rule that you can only use 80% of the circuit's rating for a continuous load.

Most EVs come these days with a charger capable of at least 32A, and up to 48A, except for low-end cheapo ones (like my old "really only for around town" Nissan LEAF, which maxes out at 27A). My wife's Model X has a 72A charger on board, but my Model S is only 48A.

If you are installing a circuit for EV charging, future proof your installation and put in at least a 50A circuit (40A charging). People who put in a 30A circuit (24A charging max) are just shortchanging themselves. The bulk of the cost of putting in a charging station is the labor involved; the incremental cost from 30A to 50A is not that much.

(*) "home level 2 chargers" is the wrong term; it's called an EVSE or charging station. For Level 1 and 2 charging, the charger is built into the car. For DC (Level 3), the charger is actually in the station.

The EVSE is just a very fancy electrical cord that has some special cutoffs and the ability to negotiate amperage delivered with the vehicles charger.


In N.A., this results in 208V being common in commercial settings (and often in apartment buildings).

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Many things need 20A circuits around the house, microwaves, disposals, dishwasher, and so on.

Do you really think those $15 non-UL listed (or any testing agency for that matter) outlets are rated over the labeled current? I would be shocked (no pun intended) if they even meet the ratings on the sticker. In fact, I would not get anywhere near the rated amps on those devices. Maybe if you are talking Jasco or Lutron would I trust the rating.

Also, you are forgetting that there are different types of loads (resistive, capacitive, inductive) and you often need a higher rated outlet for inductive devices like motors, where there is a large inrush current. Your example only discusses resistive.


I'd venture to speculate that that's because US Residential code required 2 20 Amp circuits in kitchesn since 1959, so older homes may not have it. And with only 2 required, it seems that other circuits could be 15 Amp, using cheaper 14 Gauge wire, so a mix is probably common. I'm not sure what current code actually says, but when I rewired my kitchen I pulled all 12 Gauge, and used 20 Amp breakers everyplace except the Island.

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Kitchens, dining rooms, and bathroom receptacles all require 12 gauge and 20A.



I expect that any UL-listed appliance that draws more than 15 amps under normal, continuous use would be required to have the sideways plug (NEMA 5-20P) so that it could only be connected to a 20A receptacle. I've only ever seen this on some pressure washers, air compressors, small air conditioners, etc.

It's important to note that the US NEC requirement for 20A "small appliance branch circuits" is based on worst-case loads plus a safety margin. Most of those 20A circuits will feed typical NEMA 5-15R style receptacle rated for only 15 amps, and (at least in my home) the actual appliance draws WELL under the circuit rating. For example, my microwave has a 14AWG cord while both my disposal unit and dishwasher have 16AWG cords. MANY of the items we plug into our receptacles could not safely carry the full current capacity of the circuit that powers them. The important thing to understand is that each device has a limit to the amount of current it can safely handle, and going over that limit is dangerous. For "listed" devices in Canada and the US, this limit is usually easily obtained and can be trusted. For non-listed devices, there is uncertainty and, possibly, risk.

What do folks outside of the US rely on to ensure that the electrical appliances and devices in their homes are safe? I'm aware of the CE certification, but I understand this is a self-certification my the manufacturer. Are there independent organizations that test and certify devices to meet certain standards of safety and quality?

You're asking the wrong guy... :slight_smile: I certainly wouldn't want me to be one ensuring electrical appliances are safe.

That comment was more based on what I thought was a different voltage that appliances expected in the states vs Australia. Ours are normally rated to accept / expect 220 - 240V I believe, whereas I thought that appliances in the states were typically expecting a lower voltage, which is why we can't buy larger appliances from the U.S. market.

Again my own understanding is that there are typically quite strict regulations around electrical equipment and work down here, but there are others more clued up on that than me.

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