# Size of a switch?

1. May 21, 2006

### cabellos

Why is the size of a switch determined by the stored energy that is to be interupted and by the inductance of the circuit it is connected to?

thanks,

Phil

2. May 24, 2006

### Suerbatica

When you disconnect a switch in a circuit of a given potential, it has the ability to transmit current directly through the air towards the nearest part of the switch. Since the switch is a conductive disconnecting device, the two sides of the circuit are in very close proximity to each other initially at the first point of disconnection, (over time, they obviously become further spread apart), and it is very easy for electric current to "arc" to the other side of the switch. Arcing is bad.
In the case of inductance, if no diode is placed parallel with the coil, the collapsing magnetic field of the inductor causes a voltage spike in the circuit (Its direction dependant on the fields polarity). That spike means the voltage is now higher than the source voltage and it is much easier to arc again to the other side of the switch, and at farther distances.

Switch sizes are based on their interrupt capacity. What they can safely disconnect without arcing. There are many protection methods employed. Magnetics the polarize the air against conduction of electricity, air blasting to disorganize ionized air particles for the same reason (corona voltage), mylar barriers, etc etc.

I hope this helps :)

Suer

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