N-E joined at the incomer of your house

[Kev2632]

I was just wondering with the N-E being joined at the incomer, if i was to go downstream of a circuit which was "NOT" Rcd protected and tested between Neutral and Earth that would appear as a dead short between N-E is that correct? but if i was to go downstream of a RCD protected it wont be there is at that correct? as it cant get passed the RCD is that right?

Thanks.

 

[Rockingit]

Not quite, no. An RCD is basically a measuring device, not a physical barrier (until it trips), so the N that goes in is the same N that goes out. But what you will find is that the minute you try to test the principle it will trip due to various stray currents in the system.

 

[Kev2632]

Not quite, no. An RCD is basically a measuring device, not a physical barrier (until it trips), so the N that goes in is the same N that goes out. But what you will find is that the minute you try to test the principle it will trip due to various stray currents in the system.

Yea, but why doesnt the RCD see the neutral to earth that is present at the Service point then??

 

[morph]

N-E are not joined on the consumer side

 

[Spudnik]

N-E are not joined on the consumer side

They are on a TNCS with the main switch on.:leaving:

 

[Kev2632]

N-E are not joined on the consumer side

yea, but why doesnt the neutral to earth which is joined at the incomer, continue on downstream of an RCD protected circuit, and why doesnt the RCD see this ???

 

[snowhead]

Yea, but why doesnt the RCD see the neutral to earth that is present at the Service point then??

The RCD isn't looking for N to E, it's looking for a difference in current in the L and N,( which can only have gone to E.)

 

[Kev2632]

yea i know that, but why doesnt it see that the neutral and earth are joined then? as the N has gone to E?

 

[morph]

They are on a TNCS with the main switch on.:leaving:

technicaly they are joined with the switch off too , was keeping it simple

 

[Kev2632]

technicaly they are joined with the switch off too , was keeping it simple

So how does it work then, with the RCD present in a circuit, why cant it see that there will be leakage to earth from the neutral if they are joined?? :/

 

[Guest55]

Because the rcd only monitors faults downstream to the device , not upstream towards the supply origin.

 

[Kev2632]

Because the rcd only monitors faults downstream to the device , not upstream towards the supply.

So in others words the Neutral to earth being "JOINED" at the incomer cant get passed the RCD as the Rcd only monitors what is down stream

 

[Knobhead]

The RCD is only looking at the consumer side. If it looked at the supply side NO RCD would work as at some point all systems have the neutral connected to earth.

 

[Spudnik]

I like threads like this! :clap:

 

[snowhead]

yea i know that, but why doesnt it see that the neutral and earth are joined then? as the N has gone to E?

It's not looking for (monitoring) N to E or L to E it's only monitoring L and N for missing current.
What goes up L must come back on N, if it differs by 30ma or more (or whatever the RCD rating) the RCD will trip.