What is the typical 3 phase 208V circuit breaker current limit ?

[Tofo]

To my knowledge, a typical single phase 120V single phase power supply have 20A circuit breaker (Please correct me if I were wrong). Then, what is the typical 3 phase 208V circuit breaker current limit ?

Thanks

 

[LadderLogic]

That is scary...

 

[Steve Bailey]

Tofo, to your knowledge, what is the purpose of a fuse or circuit breaker?

 

[James Mcquade]

Tofo,

in regards to 120 volts.

you have 15 amp circuits using 14 ga wire. rated at 12 amps.
12 * 1.25 (125%) = 15

you have 20 amp circuits using 12 ga wire. rated at 16 amps
16 * 1.25 (125%) = 20 amps.

this is from the nec 70 code book.


as far as the 208 volt 3 phase question.
no one can answer your question because its to vague.

from your power company, you have a main plant disconnect, then feeders, then branch circuits, then motors.

each has fuses / circuit breakers rated for the specific purpose based on load, duty cycle, heat, number of conductors in the conduit and a list of other factors that must be considered.

regards,
james

 

[Outrage]

That is scary...

Couldn't agree more. It's scary to think that people with no electrical knowledge
Are attempting machine building. It seemd like visitors to this site expect more
and more but dont have the basics to contribute themselves.

 

[FactoryTalktotheHand]

You're comparing the wiring of a building with the wiring of a control panel. Two completely different things.

There is no "typical" when it comes to breaker sizing in a control panel. There is "right" and there is "wrong," and that is determined by knowledge of code. You want to know which breaker size you should use. Based on the information you gave us, the only answer we can give you is "the right one."

 

[jraef]

Scary? Yeah, maybe, but ignorance is not a sin in and of itself. Being ignorant of something and then still thinking you are qualified to do it? That's where it gets scary.

And how about the concept of "current limit"!?

A breaker does not "current limit", it trips on excess current, meaning it STOPS the flow of current.

In the spirit of generosity though, if what you are asking is "What is the trip point of a 20A circuit breaker?", it is 20A, at least. In reality there are tolerances and allowances involved, it is not an absolute value that can be predicted with any reasonable accuracy. The PURPOSE of a circuit breaker is to protect CONDUCTORS, and the sizing rules for conductors are tailored to what the acceptable tolerances of circuit breakers entail. So to the previous point, a 20A circuit breaker is what is used to protect 12ga wire. To use 12ga wire, the load cannot continuously (defined as 3 hours or more) exceed 80% of that 20A circuit size, meaning 16A in reality. So properly applied, a 20A circuit breaker should never see more than 16A continuously, and therefore should NEVER trip. It trips when there is a PROBLEM in the circuit that causes the current to exceed the design values. If the excessive current is only 20A, it MIGHT never trip, but not likely. If the excessive current is 30A, it SHOULD trip in a matter of seconds. There is a chart for every circuit breaker that you can get from the manufacturer that shows what is called a "Time Current Curve" (TCC) that you can use to plot out an expected trip time at a specific current level if you really need to know it.

 

[VictorBit]

Scary? Yeah, maybe, but ignorance is not a sin in and of itself. Being ignorant of something and then still thinking you are qualified to do it? That's where it gets scary.


Well said Sir.

 

[Lancie1]

To my knowledge, a typical single phase 120V single phase power supply have 20A circuit breaker (Please correct me if I were wrong). Then, what is the typical 3 phase 208V circuit breaker current limit ?

Based on your knowledge, a 3-phase 208 circuit breaker should have the same trip rating as the one for a single-phase 120 volt single phase circuit THAT HAS THE SAME CURRENT. "Typical" is not a good word to use here.