# Amp Limitation on 120v Circuit

If an engineer needs to limit how many amps come out of a wall's circuit, how is this accomplished? I know that there is nothing preventing more than 15 amps from coming through my wall other than the breaker that trips if more is passed.

From my understanding of Ohm's law, you can limit the amps on a fixed voltage by increasing resistance. In order to get a 15 amp current, for example, out of a wall, instead of a huge current (which would obviously trip the breaker), what is used?

I am a bit confused on the whole way wattage and everything works, and I appreciate any responses!

• Why is a circuit breaker not good enough for you? Why do you want to limit the current? What are you ultimately trying to accomplish? – Nick Alexeev Oct 28 '15 at 22:17
• Every load has its own resistance. It'll consume exactly right amount of Amperes. For example, a typical computer consumes roughly 100 Watts, or 0.75 A from 120v grid. Therefore it'll have resistance of 500 Ohms, which will define the current (Amperes) consumed. – ilkhd Oct 28 '15 at 22:20
• $I=\dfrac{V}{R}$. Power = $\dfrac{V^2}{R}$ or $I^2R$ if you want it put another way. – Andy aka Oct 28 '15 at 22:26
• @NickAlexeev I am just trying to understand the way this stuff all works – Mad3ngineer Oct 28 '15 at 22:33

In order to limit the current drawn from a 120v socket to 15A using ohms law, you make sure that the load you attach has a resistance of at least 8 ohms.

However when you buy a kettle or toaster, it doesn't tend to say 'resistance 8 ohms' on the specification plate, it says '120v 15A'. So the simplest way to limit the current is to make sure that the rated current of the device you connect is less than 15A.

There is a sort of 'contract' you have with the socket, it agrees to supply whatever current you choose to draw, and you agree to not try to draw more than its maximum.

The breaker is there to enforce this contract. If you try to draw significantly more than the rated current, it cuts you off.