Earth

Hi
i building a small pop corn for my personal use.Every electrical hobyist knows that an earth provide safe path for faulty current to escape.I want make sure the metal case is earthed.
My question is if the live lead should touch the metal /frame casing ,how long will the earth wire provide an escape route for the faulty current before the fuse gets blown or circuit breaker trips.Which is more effecient? circuit breaker/cartridge fuse .

The both will trip within milliseconds under a short circuit, the fuse perhaps being a little faster.

the fuse will most likely blow before a circuit breaker, if you have RCDs fitted then these usually trip within 30 milliseconds.

What are you building again? A pop-corn popper?

Why not just use a small pot with a lid (like 4-quart saucepan)? Add a couple tablespoons of oil, a 1/4 cup of popcorn, and put on a stove or over a fire. Shake it occasionally (keep it on the heat, and hold the lid) and keep a listen to the corn. When you hear it start to go, start shaking it furiously like a madman until popping slows to 1-2 pops every second or so, then remove it from the heat. Season it and enjoy.

Fuses & circuit breakers are for overcurrent protection while RCDs are a different animal entirely. They are a current inbalance device that will trip if the current in the active & neutral are not the same. ie current gone missing.

In other words, an RCD is what we call a GFCI in North America.