fault protection ADS

[soulman]

hi, can anyone please explain. I've been doing a bit studying and had a total mind blank. i know when there is a earth fault, the fault travels down the earthconductor to the transformer back along the line conductor and trips the circuit breaker. Does the same happen for a short circuit fault line to neutral does it travel to the transformer and then back along the line and trip the circuit breaker.

cheers for any replies

 

[ezzzekiel]

there needs to be a complete path for the fault current to operate the cb

 

[brucelee]

yes mate
but for a pscc it travels via the neutral to the star point and back through the line

 

[LlandrilloSpark]

I had also wondered this!, cheers

 

[ezzzekiel]

as in your pfc testing where:
pscc between line and neut where neut is the return path
pefc between line and earth where earth is the return path

 

[GrannySmiff]

there is a difference between rcd protected and non.

Non the earth current will just build up and up and up until more current is pulled through the CB than it can carry and off it goes.

with RCD, earth fault travels down the earth but because it is not going back via the neutral it trips the RCD very quickly and way before the fuse rating. You need to see how a RCD works its all to do with the currents not inducing a magnetic field in the rcd as they are in balance and cancel the magnetic effects out but once out of balance (earth fault) it creates a magnetic field and trips the RCD.

Hence we use RCD for earth fault as it clears it in very small fractions of a second where as a MCB will clear it but will take allot longer.

 

[xraytek]

Does the same happen for a short circuit fault line to neutral does it travel to the transformer and then back along the line and trip the circuit breaker.

It may help if you think about why its called a 'circuit'.
The current wants to get from one side of the transformer to the other, and will do what ever it can to get there.

The amount of current that flows in the circuit depends on the voltage across the circuit and the circuit resistance, and can be calculated using Ohms Law.

 

[soulman]

cheers guys

i done this last year at college, but mostly concentrated on the earth fault loop path. so couldn,t remember