Rcd Tripped

[MeFil]

Had a fault call this afternoon.  Customer had an RCD that had tripped and wouldn't reset. 

Volex 80A 30mA rcd

Fault was traced to a neutral-earth short on one of the circuits protected by the RCD.  Sorted that out, no drama.

So, with no load on the RCD, (busbar removed) but the load-side  neutral still connected, the RCD trips.  

What is the earth fault path that is causing the rcd to trip as there should be no current flowing through the RCD in this situation?

Is it something blindingly obvious ? 

 

[Andy™]

some power will always flow N-E, could even be from a neighbours. depends on load & voltages for how much flows. sometimes its enough to trip RCD, sometimes not

 

[Evans Electric]

N-E tripping is a classic on RCDs  MeFil ....consider flicking a breaker off and cutting a cable ...RCD will trip as you cut N-E 

 

[ProDave]

Are you SURE you have fixed the N-E fault? Is there a second N-E fault?

 

[MeFil]

N-E tripping is a classic on RCDs  MeFil ....consider flicking a breaker off and cutting a cable ...RCD will trip as you cut N-E 

Yeah, I know... Was just interested in the fault 'mechanism' itself..as in what's the path.

It's late, it's friday,,, time for the pub...

Are you SURE you have fixed the N-E fault? Is there a second N-E fault?

IR'd the whole side of the board.  N-E >200 

 

[ProDave]

200 what?

 

[MeFil]

200 what?

mega ohms

 

[pewter]

My understanding is

When N touches E and makes the RCD trip is due to current flow to earth.

What is coming our the N ?

The negative side of the wave cycle.

Or so I thought.