rccb,s

[k3v1n]

im just leaning. on a tncs earthing system would a rccb trip if i touched the earth and neutral together? at a socket ect.

 

[electronicsuk]

Usually this will cause the RCD to trip, but not always. It would depend on the potential difference between neutral and earth in the system. Usually, when there's load, this difference, although small, is enough to allow 30mA to flow and trip the RCD.

 

[starspark]

yes

 

[Johnmelad502]

im just leaning. on a tncs earthing system would a rccb trip if i touched the earth and neutral together? at a socket ect.

I would have thought so myself, as this would be equivalent to a fault.

But I am not a spark and will await a definitive answer from one of them.

We are all learning

 

[ColJack]

yes.. or at least it should.. if it doesn't then the RCCB ( or RCD as they are now called ) is faulty..


the neutral and earth are only combined as far as the service head, where it splits into seperates..

the neutral then goes through the RCD.
if you short N-E at a socket then any curret flowing in the neutral will have 2 paths back to the point where they split, so only a portion will go through the RCD..

 

[k3v1n]

i was told by my boss to test the rccb, on a dual rccb ccu, the 2 test were 37ms_17m then the other 39ms_18ms and both test buttons work. but a other new starter said that if i touched the earth and neutral together the rccb would trip but it never?

 

[electronicsuk]

but a other new starter said that if i touched the earth and neutral together the rccb would trip but it never?

Did you ask him to point this out on the schedule of tests?

Also, as you were carrying out this sort of testing, are we to assume there were no loads present on the CU? If so, touching N and E together was never likely to cause the RCD to trip on TNCS.

 

[k3v1n]

i touched the neutral and earth together in the ccu all power was on but nothing pluged in

 

[Taylortwocities]

...but a other new starter said that if i touched the earth and neutral together the rccb would trip but it never?

But it didn't......

Anyways. The RCD will trip if there is a difference in potential between the neutral and earth at the point that you are connecting them together.

In a TNC-S installation, earth and neutral are connected together at the cable head. If your RCD is near that point, and there are no loads then there will probably not be enough difference in potential to cause the RCD to trip.

 

[k3v1n]

thanks lads great help

 

[electronicsuk]

In a TNC-S installation, earth and neutral are connected together at the cable head. If your RCD is near that point thwen there will probably not be enough difference in potential to cause the RCD to trip.

Indeed, and along similar lines to what I posted earlier before realising that the OP mentioned TNCS supply. However, as ColJack quite rightly pointed out, tripping is far more likely due to the alternative path for neutral current provided for loads in the system via the N-E link. With no load present during testing, and on a TNCS supply where N-E voltages are going to be more or less the same, there's no way the RCD was ever going to trip.

 

[ColJack]

did I miss out the part about current flowing in the installation again? my bad...

 

[Spark123]

Yep, if there is no current flowing in the installation then the pd wont be present across the N meter tail from the CU to the head to drive enough current down the earthing conductor to cause the RCD to trip and it will hold up.

 

[ban-all-sheds]

i was told by my boss to test the rccb,

Your boss really should know better...