I've have a GE 120V 20A circuit breaker. I'm aware that once it exceeds the 20A rating the breaker does its job and trips, but what happens if the current is less than 20A and the voltage lets says jumps to 320V. Will the breaker trip?
Electronic – Does a circuit breaker trip depending on voltage or current
accircuit breakermains
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simulate this circuit – Schematic created using CircuitLab
Figure 1. Bench test mains power supply.
How it works
- The transformer XFMR1 is a 1:1 mains power transformer. You need to figure out what's the most powerful appliance you need to test and size accordingly. e.g., for 1000 W use a 1000 VA transformer.
- The transformer will isolate the load from the mains and if there is an earth leakage fault on the appliance it will prevent your main RCD and the one on this setup from tripping. (More later.) It will also protect you while the EARTH TEST switch is open.
- The lamp serves as a current limiting test device. Open the FULL ON switch before you plug in the device. The brightness of the lamp will give an indication of the current draw. If it goes to full brightness on a small appliance, for example, you may have a short circuit but current will be limited to 0.5 A (230 V AC lamp) or 1 A (120 V AC lamp). If all appears well then switch FULL ON.
- If all is well then close the EARTH TEST fault switch. Now if there is an earth fault on the appliance some of the current will return on the earth-wire instead of the neutral (N). The RCD will detect a difference between the L and N current and trip out. This would usually only trip if there's an earth fault to a metal-cased appliance.
- Size the RCD (current rating) to protect the transformer.
That should help you sort out most problems on the bench.
The USA National Electrical Code Table 430.52 and Section 430.54 say that the the maximum setting for an instantaneous-trip breaker shall be no higher than 800% of FLA for motors other than NEMA design B high efficiency motors and no higher than 1100% for NEMA design B high efficiency motors. If that is not high enough to start the motor, the setting can be increased to 1300% or 1700% for the respective motor designs. I did not look for guidance regarding IEC motors.
I believe that starting current inrush is higher than locked rotor for the first half cycle or several half cycles and that magnetic circuit breakers can trip with one half-cycle of current above the trip rating.
I found a paper that showed a trace of motor starting current with the first half cycle peak with an RMS value of 7.4 X FLA. After that, the starting current was within 10% of 5.3 X FLA until it began to decline to normal.
M. J. Melfi and S. D. Umans, "Squirrel-Cage Induction Motors: Understanding Starting Transients," in IEEE Industry Applications Magazine, vol. 18, no. 6, pp. 28-36, Nov.-Dec. 2012
Best Answer
The vast majority of Circuit Breakers are not voltage sensitive, they are current and current/time sensitive. You can find advanced Circuit Breakers that include undervoltage sensing which are used to protect sensitive equipment from brownouts. If you like the technical details of why it is Current/Time for most breakers you could read this.
Circuit breakers are becoming more accurate and have active electronic current sensing in the most advanced units. You could read this to get a glimpse, but they are rarely voltage sensitive since the design domain means it's extremely unlikely they would ever be exposed to large changes in voltage within a given design.
For typical house type breakers the current/time curve is quite extended. Read this .....and this is a typical curve:
The curve is asymptotic at its rating, so there is no guarantee that a breaker won't ever trip with only its rated current flowing....it'll just usually take a really long time.