10A device in 15A socket vice versa?

[Dokroma]

How come you can plug in a 10amp device into a 15amp wall socket but not a 15amp device into a 10amp socket? Wouldn't plugging the 10amp device into the 15amp cause it to blow?

[TimFox]

A 15 A socket means it can tolerate currents up to 15 A, and has a fuse or circuit breaker rated for that.  What can you possibly mean here?

[Siwastaja]

The device "decides" how much current it takes. Sockets, wires, power supplies are rated for a maximum current. Generally, the wall socket and house wiring cannot actually reduce the current the device takes, the only thing it can do is to cut it completely if the limit is exceeded, using traditional fuses or modern high-tech alternatives.

[TimFox]

An ideal model for the wall socket in ones house is a constant-voltage source with a switch (circuit breaker or fuse) that opens when the current exceeds the set limit.  If you connect a shorting plug, the switch opens but the huge current will flow momentarily, long enough to flip the switch from on to off.

[garethw]

An ideal voltage source will supply what ever current is needed to keep the voltage at the desired level. For example, mains in the US is 110V (I'm in the UK so ours is 240V). If you plug in a phone charger for example, it will only draw a few hundred mA at most. That is all the circuit consumes. Plug in a kettle and suddenly you need 10A to keep the voltage at 110V. The device will consume what it needs.

A current source, however is a different story. It will generate a voltage that is required to cause a set current to flow.

If I have a 100V DC voltage source with a 1A rating and I connect a 1000 Ohm resistor across the terminals I get:
100V / 1000 Ohms = 0.1 A

If I upgrade my voltage source to a 100V DC with 100A rating and connect the same 1000 Ohm resistor I get:
100V / 1000 Ohms = 0.1 A

The current rating has no effect on the current consumed.

[vk6zgo]

How come you can plug in a 10amp device into a 15amp wall socket but not a 15amp device into a 10amp socket? Wouldn't plugging the 10amp device into the 15amp cause it to blow?

As others have said, the device draws just the amount of current it requires.
A moment's reflection reveals this is obvious------otherwise you would have trouble using things like phone chargers from the normal 10 amp sockets.

The other way around is where you can get into big trouble.----it is an evil habit in Oz amongst some sections of the community to file the large "Earth" pin on a 15 amp plug down so it fits in a normal domestic 10 amp socket.

Sometimes they get away with it!

For non-Oz folks:-
The normal 10 amp plug is similar to the Chinese one.

For 15 amp, the plug looks similar, but the "Earth" pin is made larger, so that it won't fit into a 10amp socket.

The 20 amp socket looks still looks similar, but the "Active" & "Neutral"  pins are larger, & the "Earth" pin is round.

[helius]

The other way around is where you can get into big trouble.----it is an evil habit in Oz amongst some sections of the community to file the large "Earth" pin on a 15 amp plug down so it fits in a normal domestic 10 amp socket.

Sometimes they get away with it!

In North America, a similar quick & dirty technique exists to fit a 20A plug into a 15A socket: one of the blades of the 5-20P is rotated 90 degrees from the corresponding part of a 5-15P. Take out the channellocks and twist the blade so it fits—you may get away with it if the equipment doesn't actually use more than 1800W.

[Dokroma]

How come you can plug in a 10amp device into a 15amp wall socket but not a 15amp device into a 10amp socket? Wouldn't plugging the 10amp device into the 15amp cause it to blow?

As others have said, the device draws just the amount of current it requires.
A moment's reflection reveals this is obvious------otherwise you would have trouble using things like phone chargers from the normal 10 amp sockets.

The other way around is where you can get into big trouble.----it is an evil habit in Oz amongst some sections of the community to file the large "Earth" pin on a 15 amp plug down so it fits in a normal domestic 10 amp socket.

Sometimes they get away with it!

For non-Oz folks:-
The normal 10 amp plug is similar to the Chinese one.

For 15 amp, the plug looks similar, but the "Earth" pin is made larger, so that it won't fit into a 10amp socket.

The 20 amp socket looks still looks similar, but the "Active" & "Neutral"  pins are larger, & the "Earth" pin is round.

And how does the device decide how much current it should get? Through the resistance? But then what about if the device needed 10amps exactly, wouldn't the device e.g a kettle need 0 resistance in its circuitry? But then wouldn't that cause it to blow up since don't circuits need some resistance? I am very new to electronics and amps confuse me, along with volts.

[0culus]

How come you can plug in a 10amp device into a 15amp wall socket but not a 15amp device into a 10amp socket? Wouldn't plugging the 10amp device into the 15amp cause it to blow?

Because drawing 15 amps will trip the 10 amp breaker on a 10 amp circuit. The quoted rating of a circuit is the MAXIMUM allowable current on that circuit before a protective device trips. A 15 amp circuit will happily supply 10 amps @ standard wall voltage for your area all day long.

[John B]

The 10A and 15A ratings refer to an acceptable standard of self heating in the switches, wires and power cords. Take out the circuit breaker for the moment - more than 10A or 15A is capable of flowing through either circuit, but the temperature of the whole system may rise to a dangerous level and pose a fire hazard.

Remember that the circuit breaker is to protect the rating of the circuit, the circuit isn't built to the rating of the circuit breaker (ie, the circuit safety margin should exceed the circuit breaker)

Of course, that doesn't rule out the existence of BAD wiring.

[Brumby]

You need to pay more attention to Ohms Law.  The voltage is a key part of the situation!   (Just stick to resistive loads for the moment until you get your head around this.)

The device "decides" how much current it takes.

This is the key fact ^  ^  ^  ^  ^

Sockets, wires, power supplies are rated for a maximum current.

Yes, sockets and circuits are able to supply UP TO their rated current.  Imagine you power bill if every device plugged into a 10A socket pulled 10A!!!!

You can have a device that needs 1 amp - and that's all the current it will take.  The socket cannot force any more current than that down its throat.

It is also the reason our power points in Australia - which look like these below - will allow you to insert a 10A plug into a 10, 15, 20, 25 or 32A (capacity) socket.  The same can be said for any plug - it can be inserted into a socket of matching or higher rating, but NOT into one of lower rating.

The reason for this is very straightforward....  If a device is one that may need up to, say, 20A, then if you were to plug it into a 10A capacity socket, you would almost certainly overload it - melting things, burning things and possibly setting things on fire - especially if the circuit breaker didn't trip.

This is why they are shaped the way they are.

As a simple example - if I were to plug a clock radio which requires 0.1A into a socket rated for 10A, 20A or 32A - then the current which would flow would be 0.1A in all cases.  It's the 240V (sorry, 230V  **) which is important.


** Up to 2000: 240V  +6% -10%
     From 2000: 230V +10%  -6%

[sleemanj]

But then what about if the device needed 10amps exactly, wouldn't the device e.g a kettle need 0 resistance in its circuitry?

No.  Ohm's law.

Volts = Amps x Ohms

Volts is constant in your example, the Volts coming out of your wall in Australia is 240, it doesn't change (ignoring tolerance).

The designer of the kettle decides they want to draw 10A from your 240V supply, so they use Ohm's law

Volts = Amps x Ohms

they plug in what they know

240 = 10 x Ohms

and rearrange the equation to work out what they don't know

240 / 10 = Ohms

and now they can make thier heating element be 24 Ohms, and that will draw 10A on the 240V supply.

(For sake of simplicity, I have just accepted that your imaginery designer chose 10A, rather than based their decisions on some other reasons like desirable time to heat the water and the power required to do that).

[Brumby]

And how does the device decide how much current it should get? Through the resistance? But then what about if the device needed 10amps exactly, wouldn't the device e.g a kettle need 0 resistance in its circuitry? But then wouldn't that cause it to blow up since don't circuits need some resistance? I am very new to electronics and amps confuse me, along with volts.

Yes, you certainly are confused.  It's good that you are honest about this as it shows you really want to understand.  So we will try to help you get there.

First things first...  There are sources of energy and there are consumers of energy.  (They both can be complicated - but we will stick to simple examples^*1 to help you "get it".)

Energy supplying devices come with two basic parameters:
 1. The nominal voltage they provide - which is usually fixed^*1
 2. The maximum current they are able to provide.

Energy consuming devices come with two parameters as well:
 1. The nominal voltage they are expecting - which is usually fixed^*1
 2. The amount of current they need to do their job.

Standard operating scenario:
 1. Voltages need to match (within allowed tolerances)
 2. Current required from the consuming device should be less than or equal to the maximum current the source device is able to provide.  Actual current flow is determined by the consuming device.


The Water Analogy.
It is an old analogy - but a very good one to get a grasp of a few basics....

Let's just start with a very basic example - a dam with a pipe at the bottom.

Consider voltage as pressure (in fact, voltage is sometimes referred to as electrical pressure).  The higher the voltage, the greater the pressure and vice versa.  No water needs to flow for this pressure to exist. 

Lets look at our dam with the pipe blocked off.  We could measure the pressure in the pipe.  The higher the water level, the higher the pressure.

Now let's open the pipe ... water will flow - but how much water will flow?  That will depend on the pressure and the size of the pipe (and anything along the pipe that could affect the flow of water - but don't worry about that just yet).

Next step is we run a big pipe (say 30cm dia.) to somewhere.  This pipe is capable of carrying a lot of water - but when we get to the somewhere, we connect a 1cm dia. pipe to it.  Here, the amount of water that flows depends on the smaller pipe, not the big one.

Electricity works in the same way.

[ledtester]

And how does the device decide how much current it should get? Through the resistance? But then what about if the device needed 10amps exactly, wouldn't the device e.g a kettle need 0 resistance in its circuitry? But then wouldn't that cause it to blow up since don't circuits need some resistance? I am very new to electronics and amps confuse me, along with volts.

The wall outlet provides a certain voltage and up to a certain amount of current at that voltage -- e.g. 230V and a max of 15 amps.

If the kettle needs exactly 10 A it will set its resistance to 230/10 = 23 ohms.

Of course, simple devices like kettles have a fixed resistance, so in this case the manufacturer will design the kettle to have a resistance of 23 ohms.

If you plug that kettle into a 115V outlet it will draw half as much current -- 115V/23 ohms = 5A.

This is why some devices which are made to work around the world have a switch which tells the device why kind of power (115 vs. 230) is coming in on the mains socket -- like the little red switch you find on the back of PC power supplies:

[Circlotron]

It's like saying you can safely put a 10 ton load on a 15 ton bridge, but you can't safely put a 15 ton load on a 10 ton bridge. The amps rating of the outlet is what it will tolerate, not what it supplies to any load. The load determines the amps, not the supply.

*Of course, we are talking about a voltage source here, not a current source. Let's not complicate things.

[Siwastaja]

And how does the device decide how much current it should get? Through the resistance?

Some traditional, simple devices, mostly heaters, by using a specific resistance. I = U/R.

More modern devices are, in principle, the same, except harder to analyze for a beginner because the "actual" power-hungry circuit, say a battery charger or a CPU, isn't a constant resistance, but it varies, and there are active power converters inbetween.

But then what about if the device needed 10amps exactly, wouldn't the device e.g a kettle need 0 resistance in its circuitry?

Oh, no, if the designer wants to design a kettle that draws 10A exactly, in a 110V system (now this depends on the country), they design in a 11 ohm heating element. Current = voltage / resistance. 110V / 11 ohms = 10A. Job done! Of course, if you run that kettle accidentally at 230V, say you use a plug adapter, now the 11 ohm element is taking 230V/11ohm = 20.9 A, and the kettle likely burns down.

Do also note that current ratings seldom are very accurate. If a 10A socket has a 10A fuse, it's typically guaranteed to blow only after exceeding 15A for a long time (possibly minutes), and between 10A and 15A is some grey area where it may or may not blow. Same thing for the kettle. Cheap manufacturing can't repeatably make exactly 11 ohm heating elements, and the power line voltage isn't exact either.

[tooki]

The point is, voltage is the "pressure" that forces electricity to flow through a load. (That's why excess voltage can damage a device.) The current is the amount of electricity that manages to flow given the pressure (voltage) and the resistance (think of the size of a hole in a pressurized tank).

The current rating of a device is the maximum current it wants to draw when applied to its rated voltage.

The current rating of an outlet is the maximum current it can carry safely. But it's the voltage that does the pushing, so a load will never draw more current than it wants to — the outlet can't force current through.

[Dokroma]

Ok, I understand it now. Also, what would happen if someone got shocked by a 230V outlet? What would happen? What about a 120V outlet? Also how long does it take to learn everything about electronics? I only know the names of some PCB components but I don't really know anything about how they work and stuff, but I have some experience with soldering.

[Dokroma]

Also, if I put my multimeter in Amps mode and put the probes in the socket, it would read the internal current of the multimeter right? And not 10Amps?

[Dokroma]

Also, do any of you make money off electronics? Have you ever made a circuit and put it in a case and sold it? Could I make a high quality product with little mistakes and have it made in China and sold around the globe?

[atmfjstc]

Ok, I understand it now. Also, what would happen if someone got shocked by a 230V outlet? What would happen? What about a 120V outlet?

Technically speaking, depending on the circumstances (and pure luck), a wide range of outcomes is possible, from walking away nearly unscathed, to being maimed or killed in all sorts of ways: cardiac arrest induced by the current, burns, cracking your head against something hard as you are jolted away etc etc.

Basically something you should avoid if at all possible.

[atmfjstc]

Also, if I put my multimeter in Amps mode and put the probes in the socket, it would read the internal current of the multimeter right? And not 10Amps?

A multimeter in Amps mode acts like a short across its terminals, so plugging it in the mains is the same as plugging a simple wire in the mains. Oops. Don't do it, unless you want bad things to happen to your multimeter, the socket, and possibly your hands.

[Brumby]

Also, if I put my multimeter in Amps mode and put the probes in the socket, it would read the internal current of the multimeter right? And not 10Amps?

NO!

DO NOT DO THIS!

There is a VERY BIG DIFFERENCE in using current measurements and other measurements.

This is a very softly stated description of what will happen...

A multimeter in Amps mode acts like a short across its terminals, so plugging it in the mains is the same as plugging a simple wire in the mains. Oops. Don't do it, unless you want bad things to happen to your multimeter, the socket, and possibly your hands.

[Halcyon]

Also how long does it take to learn everything about electronics? I only know the names of some PCB components but I don't really know anything about how they work and stuff, but I have some experience with soldering.

The day you stop learning in *any* trade is the day you should just give up. You never stop learning.

[tooki]

Ok, I understand it now. Also, what would happen if someone got shocked by a 230V outlet? What would happen? What about a 120V outlet? Also how long does it take to learn everything about electronics? I only know the names of some PCB components but I don't really know anything about how they work and stuff, but I have some experience with soldering.

It takes ∞ years. Because it's literally impossible to know EVERYTHING about a topic — there's always something new to learn.

I think you need to start with the basics and go from there. Don't do anything with AC yet — you're not ready.